Package Discovery and Resource Access using pkg_resources
¶
The pkg_resources
module distributed with setuptools
provides an API
for Python libraries to access their resource files, and for extensible
applications and frameworks to automatically discover plugins. It also
provides runtime support for using C extensions that are inside zipfile-format
eggs, support for merging packages that have separately-distributed modules or
subpackages, and APIs for managing Python’s current “working set” of active
packages.
Attention
Use of pkg_resources
is deprecated in favor of
importlib.resources
, importlib.metadata
and their backports (importlib_resources, importlib_metadata).
Some useful APIs are also provided by packaging (e.g. requirements
and version parsing).
Users should refrain from new usage of pkg_resources
and
should work to port to importlib-based solutions.
Overview¶
The pkg_resources
module provides runtime facilities for finding,
introspecting, activating and using installed Python distributions. Some
of the more advanced features (notably the support for parallel installation
of multiple versions) rely specifically on the “egg” format (either as a
zip archive or subdirectory), while others (such as plugin discovery) will
work correctly so long as “egg-info” metadata directories are available for
relevant distributions.
Eggs are a distribution format for Python modules, similar in concept to
Java’s “jars” or Ruby’s “gems”, or the “wheel” format defined in PEP 427.
However, unlike a pure distribution format, eggs can also be installed and
added directly to sys.path
as an import location. When installed in
this way, eggs are discoverable, meaning that they carry metadata that
unambiguously identifies their contents and dependencies. This means that
an installed egg can be automatically found and added to sys.path
in
response to simple requests of the form, “get me everything I need to use
docutils’ PDF support”. This feature allows mutually conflicting versions of
a distribution to co-exist in the same Python installation, with individual
applications activating the desired version at runtime by manipulating the
contents of sys.path
(this differs from the virtual environment
approach, which involves creating isolated environments for each
application).
The following terms are needed in order to explain the capabilities offered by this module:
- project
A library, framework, script, plugin, application, or collection of data or other resources, or some combination thereof. Projects are assumed to have “relatively unique” names, e.g. names registered with PyPI.
- release
A snapshot of a project at a particular point in time, denoted by a version identifier.
- distribution
A file or files that represent a particular release.
- importable distribution
A file or directory that, if placed on
sys.path
, allows Python to import any modules contained within it.- pluggable distribution
An importable distribution whose filename unambiguously identifies its release (i.e. project and version), and whose contents unambiguously specify what releases of other projects will satisfy its runtime requirements.
- extra
An “extra” is an optional feature of a release, that may impose additional runtime requirements. For example, if docutils PDF support required a PDF support library to be present, docutils could define its PDF support as an “extra”, and list what other project releases need to be available in order to provide it.
- environment
A collection of distributions potentially available for importing, but not necessarily active. More than one distribution (i.e. release version) for a given project may be present in an environment.
- working set
A collection of distributions actually available for importing, as on
sys.path
. At most one distribution (release version) of a given project may be present in a working set, as otherwise there would be ambiguity as to what to import.- eggs
Eggs are pluggable distributions in one of the three formats currently supported by
pkg_resources
. There are built eggs, development eggs, and egg links. Built eggs are directories or zipfiles whose name ends with.egg
and follows the egg naming conventions, and contain anEGG-INFO
subdirectory (zipped or otherwise). Development eggs are normal directories of Python code with one or moreProjectName.egg-info
subdirectories. The development egg format is also used to provide a default version of a distribution that is available to software that doesn’t usepkg_resources
to request specific versions. Egg links are*.egg-link
files that contain the name of a built or development egg, to support symbolic linking on platforms that do not have native symbolic links (or where the symbolic link support is limited).
(For more information about these terms and concepts, see also this
architectural overview of pkg_resources
and Python Eggs in general.)
API Reference¶
Namespace Package Support¶
A namespace package is a package that only contains other packages and modules,
with no direct contents of its own. Such packages can be split across
multiple, separately-packaged distributions. They are normally used to split
up large packages produced by a single organization, such as in the zope
namespace package for Zope Corporation packages, and the peak
namespace
package for the Python Enterprise Application Kit.
To create a namespace package, you list it in the namespace_packages
argument to setup()
, in your project’s setup.py
. (See the
setuptools documentation on namespace packages for
more information on this.) Also, you must add a declare_namespace()
call
in the package’s __init__.py
file(s):
declare_namespace(name)
Declare that the dotted package name
name
is a “namespace package” whose contained packages and modules may be spread across multiple distributions. The named package’s__path__
will be extended to include the corresponding package in all distributions onsys.path
that contain a package of that name. (More precisely, if an importer’sfind_module(name)
returns a loader, then it will also be searched for the package’s contents.) Whenever a Distribution’sactivate()
method is invoked, it checks for the presence of namespace packages and updates their__path__
contents accordingly.
Applications that manipulate namespace packages or directly alter sys.path
at runtime may also need to use this API function:
fixup_namespace_packages(path_item)
Declare that
path_item
is a newly added item onsys.path
that may need to be used to update existing namespace packages. Ordinarily, this is called for you when an egg is automatically added tosys.path
, but if your application modifiessys.path
to include locations that may contain portions of a namespace package, you will need to call this function to ensure they are added to the existing namespace packages.
Although by default pkg_resources
only supports namespace packages for
filesystem and zip importers, you can extend its support to other “importers”
compatible with PEP 302 using the register_namespace_handler()
function.
See the section below on Supporting Custom Importers for details.
WorkingSet
Objects¶
The WorkingSet
class provides access to a collection of “active”
distributions. In general, there is only one meaningful WorkingSet
instance: the one that represents the distributions that are currently active
on sys.path
. This global instance is available under the name
working_set
in the pkg_resources
module. However, specialized
tools may wish to manipulate working sets that don’t correspond to
sys.path
, and therefore may wish to create other WorkingSet
instances.
It’s important to note that the global working_set
object is initialized
from sys.path
when pkg_resources
is first imported, but is only updated
if you do all future sys.path
manipulation via pkg_resources
APIs. If
you manually modify sys.path
, you must invoke the appropriate methods on
the working_set
instance to keep it in sync. Unfortunately, Python does
not provide any way to detect arbitrary changes to a list object like
sys.path
, so pkg_resources
cannot automatically update the
working_set
based on changes to sys.path
.
WorkingSet(entries=None)
Create a
WorkingSet
from an iterable of path entries. Ifentries
is not supplied, it defaults to the value ofsys.path
at the time the constructor is called.Note that you will not normally construct
WorkingSet
instances yourself, but instead you will implicitly or explicitly use the globalworking_set
instance. For the most part, thepkg_resources
API is designed so that theworking_set
is used by default, such that you don’t have to explicitly refer to it most of the time.
All distributions available directly on sys.path
will be activated
automatically when pkg_resources
is imported. This behaviour can cause
version conflicts for applications which require non-default versions of
those distributions. To handle this situation, pkg_resources
checks for a
__requires__
attribute in the __main__
module when initializing the
default working set, and uses this to ensure a suitable version of each
affected distribution is activated. For example:
__requires__ = ["CherryPy < 3"] # Must be set before pkg_resources import
import pkg_resources
Basic WorkingSet
Methods¶
The following methods of WorkingSet
objects are also available as
module-level functions in pkg_resources
that apply to the default
working_set
instance. Thus, you can use e.g. pkg_resources.require()
as an abbreviation for pkg_resources.working_set.require()
:
require(*requirements)
Ensure that distributions matching
requirements
are activatedrequirements
must be a string or a (possibly-nested) sequence thereof, specifying the distributions and versions required. The return value is a sequence of the distributions that needed to be activated to fulfill the requirements; all relevant distributions are included, even if they were already activated in this working set.For the syntax of requirement specifiers, see the section below on Requirements Parsing.
In general, it should not be necessary for you to call this method directly. It’s intended more for use in quick-and-dirty scripting and interactive interpreter hacking than for production use. If you’re creating an actual library or application, it’s strongly recommended that you create a “setup.py” script using
setuptools
, and declare all your requirements there. That way, tools like pip can automatically detect what requirements your package has, and deal with them accordingly.Note that calling
require('SomePackage')
will not installSomePackage
if it isn’t already present. If you need to do this, you should use theresolve()
method instead, which allows you to pass aninstaller
callback that will be invoked when a needed distribution can’t be found on the local machine. You can then have this callback display a dialog, automatically download the needed distribution, or whatever else is appropriate for your application. See the documentation below on theresolve()
method for more information, and also on theobtain()
method ofEnvironment
objects.run_script(requires, script_name)
Locate distribution specified by
requires
and run itsscript_name
script.requires
must be a string containing a requirement specifier. (See Requirements Parsing below for the syntax.)The script, if found, will be executed in the caller’s globals. That’s because this method is intended to be called from wrapper scripts that act as a proxy for the “real” scripts in a distribution. A wrapper script usually doesn’t need to do anything but invoke this function with the correct arguments.
If you need more control over the script execution environment, you probably want to use the
run_script()
method of aDistribution
object’s Metadata API instead.iter_entry_points(group, name=None)
Yield entry point objects from
group
matchingname
If
name
is None, yields all entry points ingroup
from all distributions in the working set, otherwise only ones matching bothgroup
andname
are yielded. Entry points are yielded from the active distributions in the order that the distributions appear in the working set. (For the globalworking_set
, this should be the same as the order that they are listed insys.path
.) Note that within the entry points advertised by an individual distribution, there is no particular ordering.Please see the section below on Entry Points for more information.
WorkingSet
Methods and Attributes¶
These methods are used to query or manipulate the contents of a specific
working set, so they must be explicitly invoked on a particular WorkingSet
instance:
add_entry(entry)
Add a path item to the
entries
, finding any distributions on it. You should use this when you add additional items tosys.path
and you want the globalworking_set
to reflect the change. This method is also called by theWorkingSet()
constructor during initialization.This method uses
find_distributions(entry,True)
to find distributions corresponding to the path entry, and thenadd()
them.entry
is always appended to theentries
attribute, even if it is already present, however. (This is becausesys.path
can contain the same value more than once, and theentries
attribute should be able to reflect this.)__contains__(dist)
True if
dist
is active in thisWorkingSet
. Note that only one distribution for a given project can be active in a givenWorkingSet
.__iter__()
Yield distributions for non-duplicate projects in the working set. The yield order is the order in which the items’ path entries were added to the working set.
find(req)
Find a distribution matching
req
(aRequirement
instance). If there is an active distribution for the requested project, this returns it, as long as it meets the version requirement specified byreq
. But, if there is an active distribution for the project and it does not meet thereq
requirement,VersionConflict
is raised. If there is no active distribution for the requested project,None
is returned.resolve(requirements, env=None, installer=None)
List all distributions needed to (recursively) meet
requirements
requirements
must be a sequence ofRequirement
objects.env
, if supplied, should be anEnvironment
instance. If not supplied, anEnvironment
is created from the working set’sentries
.installer
, if supplied, will be invoked with each requirement that cannot be met by an already-installed distribution; it should return aDistribution
orNone
. (See theobtain()
method of Environment Objects, below, for more information on theinstaller
argument.)add(dist, entry=None)
Add
dist
to working set, associated withentry
If
entry
is unspecified, it defaults todist.location
. On exit from this routine,entry
is added to the end of the working set’s.entries
(if it wasn’t already present).dist
is only added to the working set if it’s for a project that doesn’t already have a distribution active in the set. If it’s successfully added, any callbacks registered with thesubscribe()
method will be called. (See Receiving Change Notifications, below.)Note:
add()
is automatically called for you by therequire()
method, so you don’t normally need to use this method directly.entries
This attribute represents a “shadow”
sys.path
, primarily useful for debugging. If you are experiencing import problems, you should check the globalworking_set
object’sentries
againstsys.path
, to ensure that they match. If they do not, then some part of your program is manipulatingsys.path
without updating theworking_set
accordingly. IMPORTANT NOTE: do not directly manipulate this attribute! Setting it equal tosys.path
will not fix your problem, any more than putting black tape over an “engine warning” light will fix your car! If this attribute is out of sync withsys.path
, it’s merely an indicator of the problem, not the cause of it.
Receiving Change Notifications¶
Extensible applications and frameworks may need to receive notification when
a new distribution (such as a plug-in component) has been added to a working
set. This is what the subscribe()
method and add_activation_listener()
function are for.
subscribe(callback)
Invoke
callback(distribution)
once for each active distribution that is in the set now, or gets added later. Because the callback is invoked for already-active distributions, you do not need to loop over the working set yourself to deal with the existing items; just register the callback and be prepared for the fact that it will be called immediately by this method.Note that callbacks must not allow exceptions to propagate, or they will interfere with the operation of other callbacks and possibly result in an inconsistent working set state. Callbacks should use a try/except block to ignore, log, or otherwise process any errors, especially since the code that caused the callback to be invoked is unlikely to be able to handle the errors any better than the callback itself.
pkg_resources.add_activation_listener()
is an alternate spelling of
pkg_resources.working_set.subscribe()
.
Locating Plugins¶
Extensible applications will sometimes have a “plugin directory” or a set of
plugin directories, from which they want to load entry points or other
metadata. The find_plugins()
method allows you to do this, by scanning an
environment for the newest version of each project that can be safely loaded
without conflicts or missing requirements.
find_plugins(plugin_env, full_env=None, fallback=True)
Scan
plugin_env
and identify which distributions could be added to this working set without version conflicts or missing requirements.Example usage:
distributions, errors = working_set.find_plugins( Environment(plugin_dirlist) ) map(working_set.add, distributions) # add plugins+libs to sys.path print "Couldn't load", errors # display errors
The
plugin_env
should be anEnvironment
instance that contains only distributions that are in the project’s “plugin directory” or directories. Thefull_env
, if supplied, should be anEnvironment
instance that contains all currently-available distributions.If
full_env
is not supplied, one is created automatically from theWorkingSet
this method is called on, which will typically mean that every directory onsys.path
will be scanned for distributions.This method returns a 2-tuple: (
distributions
,error_info
), wheredistributions
is a list of the distributions found inplugin_env
that were loadable, along with any other distributions that are needed to resolve their dependencies.error_info
is a dictionary mapping unloadable plugin distributions to an exception instance describing the error that occurred. Usually this will be aDistributionNotFound
orVersionConflict
instance.Most applications will use this method mainly on the master
working_set
instance inpkg_resources
, and then immediately add the returned distributions to the working set so that they are available on sys.path. This will make it possible to find any entry points, and allow any other metadata tracking and hooks to be activated.The resolution algorithm used by
find_plugins()
is as follows. First, the project names of the distributions present inplugin_env
are sorted. Then, each project’s eggs are tried in descending version order (i.e., newest version first).An attempt is made to resolve each egg’s dependencies. If the attempt is successful, the egg and its dependencies are added to the output list and to a temporary copy of the working set. The resolution process continues with the next project name, and no older eggs for that project are tried.
If the resolution attempt fails, however, the error is added to the error dictionary. If the
fallback
flag is true, the next older version of the plugin is tried, until a working version is found. If false, the resolution process continues with the next plugin project name.Some applications may have stricter fallback requirements than others. For example, an application that has a database schema or persistent objects may not be able to safely downgrade a version of a package. Others may want to ensure that a new plugin configuration is either 100% good or else revert to a known-good configuration. (That is, they may wish to revert to a known configuration if the
error_info
return value is non-empty.)Note that this algorithm gives precedence to satisfying the dependencies of alphabetically prior project names in case of version conflicts. If two projects named “AaronsPlugin” and “ZekesPlugin” both need different versions of “TomsLibrary”, then “AaronsPlugin” will win and “ZekesPlugin” will be disabled due to version conflict.
Environment
Objects¶
An “environment” is a collection of Distribution
objects, usually ones
that are present and potentially importable on the current platform.
Environment
objects are used by pkg_resources
to index available
distributions during dependency resolution.
Environment(search_path=None, platform=get_supported_platform(), python=PY_MAJOR)
Create an environment snapshot by scanning
search_path
for distributions compatible withplatform
andpython
.search_path
should be a sequence of strings such as might be used onsys.path
. If asearch_path
isn’t supplied,sys.path
is used.platform
is an optional string specifying the name of the platform that platform-specific distributions must be compatible with. If unspecified, it defaults to the current platform.python
is an optional string naming the desired version of Python (e.g.'2.4'
); it defaults to the currently-running version.You may explicitly set
platform
(and/orpython
) toNone
if you wish to include all distributions, not just those compatible with the running platform or Python version.Note that
search_path
is scanned immediately for distributions, and the resultingEnvironment
is a snapshot of the found distributions. It is not automatically updated if the system’s state changes due to e.g. installation or removal of distributions.__getitem__(project_name)
Returns a list of distributions for the given project name, ordered from newest to oldest version. (And highest to lowest format precedence for distributions that contain the same version of the project.) If there are no distributions for the project, returns an empty list.
__iter__()
Yield the unique project names of the distributions in this environment. The yielded names are always in lower case.
add(dist)
Add
dist
to the environment if it matches the platform and python version specified at creation time, and only if the distribution hasn’t already been added. (i.e., adding the same distribution more than once is a no-op.)remove(dist)
Remove
dist
from the environment.can_add(dist)
Is distribution
dist
acceptable for this environment? If it’s not compatible with theplatform
andpython
version values specified when the environment was created, a false value is returned.__add__(dist_or_env)
(+
operator)Add a distribution or environment to an
Environment
instance, returning a new environment object that contains all the distributions previously contained by both. The new environment will have aplatform
andpython
ofNone
, meaning that it will not reject any distributions from being added to it; it will simply accept whatever is added. If you want the added items to be filtered for platform and Python version, or you want to add them to the same environment instance, you should use in-place addition (+=
) instead.__iadd__(dist_or_env)
(+=
operator)Add a distribution or environment to an
Environment
instance in-place, updating the existing instance and returning it. Theplatform
andpython
filter attributes take effect, so distributions in the source that do not have a suitable platform string or Python version are silently ignored.best_match(req, working_set, installer=None)
Find distribution best matching
req
and usable onworking_set
This calls the
find(req)
method of theworking_set
to see if a suitable distribution is already active. (This may raiseVersionConflict
if an unsuitable version of the project is already active in the specifiedworking_set
.) If a suitable distribution isn’t active, this method returns the newest distribution in the environment that meets theRequirement
inreq
. If no suitable distribution is found, andinstaller
is supplied, then the result of calling the environment’sobtain(req, installer)
method will be returned.obtain(requirement, installer=None)
Obtain a distro that matches requirement (e.g. via download). In the base
Environment
class, this routine just returnsinstaller(requirement)
, unlessinstaller
is None, in which case None is returned instead. This method is a hook that allows subclasses to attempt other ways of obtaining a distribution before falling back to theinstaller
argument.scan(search_path=None)
Scan
search_path
for distributions usable onplatform
Any distributions found are added to the environment.
search_path
should be a sequence of strings such as might be used onsys.path
. If not supplied,sys.path
is used. Only distributions conforming to the platform/python version defined at initialization are added. This method is a shortcut for using thefind_distributions()
function to find the distributions from each item insearch_path
, and then callingadd()
to add each one to the environment.
Requirement
Objects¶
Requirement
objects express what versions of a project are suitable for
some purpose. These objects (or their string form) are used by various
pkg_resources
APIs in order to find distributions that a script or
distribution needs.
Requirements Parsing¶
parse_requirements(s)
Yield
Requirement
objects for a string or iterable of lines. Each requirement must start on a new line. See below for syntax.Requirement.parse(s)
Create a
Requirement
object from a string or iterable of lines. AValueError
is raised if the string or lines do not contain a valid requirement specifier, or if they contain more than one specifier. (To parse multiple specifiers from a string or iterable of strings, useparse_requirements()
instead.)The syntax of a requirement specifier is defined in full in PEP 508.
Some examples of valid requirement specifiers:
FooProject >= 1.2 Fizzy [foo, bar] PickyThing>1.6,<=1.9,!=1.8.6 SomethingWhoseVersionIDontCareAbout SomethingWithMarker[foo]>1.0;python_version<"2.7"
The project name is the only required portion of a requirement string, and if it’s the only thing supplied, the requirement will accept any version of that project.
The “extras” in a requirement are used to request optional features of a project, that may require additional project distributions in order to function. For example, if the hypothetical “Report-O-Rama” project offered optional PDF support, it might require an additional library in order to provide that support. Thus, a project needing Report-O-Rama’s PDF features could use a requirement of
Report-O-Rama[PDF]
to request installation or activation of both Report-O-Rama and any libraries it needs in order to provide PDF support. For example, you could use:pip install Report-O-Rama[PDF]
To install the necessary packages using pip, or call
pkg_resources.require('Report-O-Rama[PDF]')
to add the necessary distributions to sys.path at runtime.The “markers” in a requirement are used to specify when a requirement should be installed – the requirement will be installed if the marker evaluates as true in the current environment. For example, specifying
argparse;python_version<"3.0"
will not install in an Python 3 environment, but will in a Python 2 environment.
Requirement
Methods and Attributes¶
__contains__(dist_or_version)
Return true if
dist_or_version
fits the criteria for this requirement. Ifdist_or_version
is aDistribution
object, its project name must match the requirement’s project name, and its version must meet the requirement’s version criteria. Ifdist_or_version
is a string, it is parsed using theparse_version()
utility function. Otherwise, it is assumed to be an already-parsed version.The
Requirement
object’s version specifiers (.specs
) are internally sorted into ascending version order, and used to establish what ranges of versions are acceptable. Adjacent redundant conditions are effectively consolidated (e.g.">1, >2"
produces the same results as">2"
, and"<2,<3"
produces the same results as"<2"
)."!="
versions are excised from the ranges they fall within. The version being tested for acceptability is then checked for membership in the resulting ranges.__eq__(other_requirement)
A requirement compares equal to another requirement if they have case-insensitively equal project names, version specifiers, and “extras”. (The order that extras and version specifiers are in is also ignored.) Equal requirements also have equal hashes, so that requirements can be used in sets or as dictionary keys.
__str__()
The string form of a
Requirement
is a string that, if passed toRequirement.parse()
, would return an equalRequirement
object.project_name
The name of the required project
key
An all-lowercase version of the
project_name
, useful for comparison or indexing.extras
A tuple of names of “extras” that this requirement calls for. (These will be all-lowercase and normalized using the
safe_extra()
parsing utility function, so they may not exactly equal the extras the requirement was created with.)specs
A list of
(op,version)
tuples, sorted in ascending parsed-version order. Theop
in each tuple is a comparison operator, represented as a string. Theversion
is the (unparsed) version number.marker
An instance of
packaging.markers.Marker
that allows evaluation against the current environment. May be None if no marker specified.url
The location to download the requirement from if specified.
Entry Points¶
Entry points are a simple way for distributions to “advertise” Python objects (such as functions or classes) for use by other distributions. Extensible applications and frameworks can search for entry points with a particular name or group, either from a specific distribution or from all active distributions on sys.path, and then inspect or load the advertised objects at will.
Entry points belong to “groups” which are named with a dotted name similar to
a Python package or module name. For example, the setuptools
package uses
an entry point named distutils.commands
in order to find commands defined
by distutils extensions. setuptools
treats the names of entry points
defined in that group as the acceptable commands for a setup script.
In a similar way, other packages can define their own entry point groups,
either using dynamic names within the group (like distutils.commands
), or
possibly using predefined names within the group. For example, a blogging
framework that offers various pre- or post-publishing hooks might define an
entry point group and look for entry points named “pre_process” and
“post_process” within that group.
To advertise an entry point, a project needs to use setuptools
and provide
an entry_points
argument to setup()
in its setup script, so that the
entry points will be included in the distribution’s metadata. For more
details, see Advertising Behavior.
Each project distribution can advertise at most one entry point of a given
name within the same entry point group. For example, a distutils extension
could advertise two different distutils.commands
entry points, as long as
they had different names. However, there is nothing that prevents different
projects from advertising entry points of the same name in the same group. In
some cases, this is a desirable thing, since the application or framework that
uses the entry points may be calling them as hooks, or in some other way
combining them. It is up to the application or framework to decide what to do
if multiple distributions advertise an entry point; some possibilities include
using both entry points, displaying an error message, using the first one found
in sys.path order, etc.
Convenience API¶
In the following functions, the dist
argument can be a Distribution
instance, a Requirement
instance, or a string specifying a requirement
(i.e. project name, version, etc.). If the argument is a string or
Requirement
, the specified distribution is located (and added to sys.path
if not already present). An error will be raised if a matching distribution is
not available.
The group
argument should be a string containing a dotted identifier,
identifying an entry point group. If you are defining an entry point group,
you should include some portion of your package’s name in the group name so as
to avoid collision with other packages’ entry point groups.
load_entry_point(dist, group, name)
Load the named entry point from the specified distribution, or raise
ImportError
.get_entry_info(dist, group, name)
Return an
EntryPoint
object for the givengroup
andname
from the specified distribution. ReturnsNone
if the distribution has not advertised a matching entry point.get_entry_map(dist, group=None)
Return the distribution’s entry point map for
group
, or the full entry map for the distribution. This function always returns a dictionary, even if the distribution advertises no entry points. Ifgroup
is given, the dictionary maps entry point names to the correspondingEntryPoint
object. Ifgroup
is None, the dictionary maps group names to dictionaries that then map entry point names to the correspondingEntryPoint
instance in that group.iter_entry_points(group, name=None)
Yield entry point objects from
group
matchingname
.If
name
is None, yields all entry points ingroup
from all distributions in the working set on sys.path, otherwise only ones matching bothgroup
andname
are yielded. Entry points are yielded from the active distributions in the order that the distributions appear on sys.path. (Within entry points for a particular distribution, however, there is no particular ordering.)(This API is actually a method of the global
working_set
object; see the section above on Basic WorkingSet Methods for more information.)
Creating and Parsing¶
EntryPoint(name, module_name, attrs=(), extras=(), dist=None)
Create an
EntryPoint
instance.name
is the entry point name. Themodule_name
is the (dotted) name of the module containing the advertised object.attrs
is an optional tuple of names to look up from the module to obtain the advertised object. For example, anattrs
of("foo","bar")
and amodule_name
of"baz"
would mean that the advertised object could be obtained by the following code:import baz advertised_object = baz.foo.bar
The
extras
are an optional tuple of “extra feature” names that the distribution needs in order to provide this entry point. When the entry point is loaded, these extra features are looked up in thedist
argument to find out what other distributions may need to be activated on sys.path; see theload()
method for more details. Theextras
argument is only meaningful ifdist
is specified.dist
must be aDistribution
instance.EntryPoint.parse(src, dist=None)
(classmethod)Parse a single entry point from string
src
Entry point syntax follows the form:
name = some.module:some.attr [extra1,extra2]
The entry name and module name are required, but the
:attrs
and[extras]
parts are optional, as is the whitespace shown between some of the items. Thedist
argument is passed through to theEntryPoint()
constructor, along with the other values parsed fromsrc
.EntryPoint.parse_group(group, lines, dist=None)
(classmethod)Parse
lines
(a string or sequence of lines) to create a dictionary mapping entry point names toEntryPoint
objects.ValueError
is raised if entry point names are duplicated, ifgroup
is not a valid entry point group name, or if there are any syntax errors. (Note: thegroup
parameter is used only for validation and to create more informative error messages.) Ifdist
is provided, it will be used to set thedist
attribute of the createdEntryPoint
objects.EntryPoint.parse_map(data, dist=None)
(classmethod)Parse
data
into a dictionary mapping group names to dictionaries mapping entry point names toEntryPoint
objects. Ifdata
is a dictionary, then the keys are used as group names and the values are passed toparse_group()
as thelines
argument. Ifdata
is a string or sequence of lines, it is first split into .ini-style sections (using thesplit_sections()
utility function) and the section names are used as group names. In either case, thedist
argument is passed through toparse_group()
so that the entry points will be linked to the specified distribution.
EntryPoint
Objects¶
For simple introspection, EntryPoint
objects have attributes that
correspond exactly to the constructor argument names: name
,
module_name
, attrs
, extras
, and dist
are all available. In
addition, the following methods are provided:
load()
Load the entry point, returning the advertised Python object. Effectively calls
self.require()
then returnsself.resolve()
.require(env=None, installer=None)
Ensure that any “extras” needed by the entry point are available on sys.path.
UnknownExtra
is raised if theEntryPoint
hasextras
, but nodist
, or if the named extras are not defined by the distribution. Ifenv
is supplied, it must be anEnvironment
, and it will be used to search for needed distributions if they are not already present on sys.path. Ifinstaller
is supplied, it must be a callable taking aRequirement
instance and returning a matching importableDistribution
instance or None.resolve()
Resolve the entry point from its module and attrs, returning the advertised Python object. Raises
ImportError
if it cannot be obtained.__str__()
The string form of an
EntryPoint
is a string that could be passed toEntryPoint.parse()
to produce an equivalentEntryPoint
.
Distribution
Objects¶
Distribution
objects represent collections of Python code that may or may
not be importable, and may or may not have metadata and resources associated
with them. Their metadata may include information such as what other projects
the distribution depends on, what entry points the distribution advertises, and
so on.
Getting or Creating Distributions¶
Most commonly, you’ll obtain Distribution
objects from a WorkingSet
or
an Environment
. (See the sections above on WorkingSet Objects and
Environment Objects, which are containers for active distributions and
available distributions, respectively.) You can also obtain Distribution
objects from one of these high-level APIs:
find_distributions(path_item, only=False)
Yield distributions accessible via
path_item
. Ifonly
is true, yield only distributions whoselocation
is equal topath_item
. In other words, ifonly
is true, this yields any distributions that would be importable ifpath_item
were onsys.path
. Ifonly
is false, this also yields distributions that are “in” or “under”path_item
, but would not be importable unless their locations were also added tosys.path
.get_distribution(dist_spec)
Return a
Distribution
object for a givenRequirement
or string. Ifdist_spec
is already aDistribution
instance, it is returned. If it is aRequirement
object or a string that can be parsed into one, it is used to locate and activate a matching distribution, which is then returned.
However, if you’re creating specialized tools for working with distributions,
or creating a new distribution format, you may also need to create
Distribution
objects directly, using one of the three constructors below.
These constructors all take an optional metadata
argument, which is used to
access any resources or metadata associated with the distribution. metadata
must be an object that implements the IResourceProvider
interface, or None.
If it is None, an EmptyProvider
is used instead. Distribution
objects
implement both the IResourceProvider and IMetadataProvider Methods by
delegating them to the metadata
object.
Distribution.from_location(location, basename, metadata=None, **kw)
(classmethod)Create a distribution for
location
, which must be a string such as a URL, filename, or other string that might be used onsys.path
.basename
is a string naming the distribution, likeFoo-1.2-py2.4.egg
. Ifbasename
ends with.egg
, then the project’s name, version, python version and platform are extracted from the filename and used to set those properties of the created distribution. Any additional keyword arguments are forwarded to theDistribution()
constructor.Distribution.from_filename(filename, metadata=None**kw)
(classmethod)Create a distribution by parsing a local filename. This is a shorter way of saying
Distribution.from_location(normalize_path(filename), os.path.basename(filename), metadata)
. In other words, it creates a distribution whose location is the normalize form of the filename, parsing name and version information from the base portion of the filename. Any additional keyword arguments are forwarded to theDistribution()
constructor.Distribution(location,metadata,project_name,version,py_version,platform,precedence)
Create a distribution by setting its properties. All arguments are optional and default to None, except for
py_version
(which defaults to the current Python version) andprecedence
(which defaults toEGG_DIST
; for more details seeprecedence
under Distribution Attributes below). Note that it’s usually easier to use thefrom_filename()
orfrom_location()
constructors than to specify all these arguments individually.
Distribution
Attributes¶
- location
A string indicating the distribution’s location. For an importable distribution, this is the string that would be added to
sys.path
to make it actively importable. For non-importable distributions, this is simply a filename, URL, or other way of locating the distribution.- project_name
A string, naming the project that this distribution is for. Project names are defined by a project’s setup script, and they are used to identify projects on PyPI. When a
Distribution
is constructed, theproject_name
argument is passed through thesafe_name()
utility function to filter out any unacceptable characters.- key
dist.key
is short fordist.project_name.lower()
. It’s used for case-insensitive comparison and indexing of distributions by project name.- extras
A list of strings, giving the names of extra features defined by the project’s dependency list (the
extras_require
argument specified in the project’s setup script).- version
A string denoting what release of the project this distribution contains. When a
Distribution
is constructed, theversion
argument is passed through thesafe_version()
utility function to filter out any unacceptable characters. If noversion
is specified at construction time, then attempting to access this attribute later will cause theDistribution
to try to discover its version by reading itsPKG-INFO
metadata file. IfPKG-INFO
is unavailable or can’t be parsed,ValueError
is raised.- parsed_version
The
parsed_version
is an object representing a “parsed” form of the distribution’sversion
.dist.parsed_version
is a shortcut for callingparse_version(dist.version)
. It is used to compare or sort distributions by version. (See the Parsing Utilities section below for more information on theparse_version()
function.) Note that accessingparsed_version
may result in aValueError
if theDistribution
was constructed without aversion
and withoutmetadata
capable of supplying the missing version info.- py_version
The major/minor Python version the distribution supports, as a string. For example, “2.7” or “3.4”. The default is the current version of Python.
- platform
A string representing the platform the distribution is intended for, or
None
if the distribution is “pure Python” and therefore cross-platform. See Platform Utilities below for more information on platform strings.- precedence
A distribution’s
precedence
is used to determine the relative order of two distributions that have the sameproject_name
andparsed_version
. The default precedence ispkg_resources.EGG_DIST
, which is the highest (i.e. most preferred) precedence. The full list of predefined precedences, from most preferred to least preferred, is:EGG_DIST
,BINARY_DIST
,SOURCE_DIST
,CHECKOUT_DIST
, andDEVELOP_DIST
. Normally, precedences other thanEGG_DIST
are used only by thesetuptools.package_index
module, when sorting distributions found in a package index to determine their suitability for installation. “System” and “Development” eggs (i.e., ones that use the.egg-info
format), however, are automatically given a precedence ofDEVELOP_DIST
.
Distribution
Methods¶
activate(path=None)
Ensure distribution is importable on
path
. Ifpath
is None,sys.path
is used instead. This ensures that the distribution’slocation
is in thepath
list, and it also performs any necessary namespace package fixups or declarations. (That is, if the distribution contains namespace packages, this method ensures that they are declared, and that the distribution’s contents for those namespace packages are merged with the contents provided by any other active distributions. See the section above on Namespace Package Support for more information.)pkg_resources
adds a notification callback to the globalworking_set
that ensures this method is called whenever a distribution is added to it. Therefore, you should not normally need to explicitly call this method. (Note that this means that namespace packages onsys.path
are always imported as soon aspkg_resources
is, which is another reason why namespace packages should not contain any code or import statements.)as_requirement()
Return a
Requirement
instance that matches this distribution’s project name and version.requires(extras=())
List the
Requirement
objects that specify this distribution’s dependencies. Ifextras
is specified, it should be a sequence of names of “extras” defined by the distribution, and the list returned will then include any dependencies needed to support the named “extras”.clone(**kw)
Create a copy of the distribution. Any supplied keyword arguments override the corresponding argument to the
Distribution()
constructor, allowing you to change some of the copied distribution’s attributes.egg_name()
Return what this distribution’s standard filename should be, not including the “.egg” extension. For example, a distribution for project “Foo” version 1.2 that runs on Python 2.3 for Windows would have an
egg_name()
ofFoo-1.2-py2.3-win32
. Any dashes in the name or version are converted to underscores. (Distribution.from_location()
will convert them back when parsing a “.egg” file name.)__cmp__(other)
,__hash__()
Distribution objects are hashed and compared on the basis of their parsed version and precedence, followed by their key (lowercase project name), location, Python version, and platform.
The following methods are used to access EntryPoint
objects advertised
by the distribution. See the section above on Entry Points for more
detailed information about these operations:
get_entry_info(group, name)
Return the
EntryPoint
object forgroup
andname
, or None if no such point is advertised by this distribution.get_entry_map(group=None)
Return the entry point map for
group
. Ifgroup
is None, return a dictionary mapping group names to entry point maps for all groups. (An entry point map is a dictionary of entry point names toEntryPoint
objects.)load_entry_point(group, name)
Short for
get_entry_info(group, name).load()
. Returns the object advertised by the named entry point, or raisesImportError
if the entry point isn’t advertised by this distribution, or there is some other import problem.
In addition to the above methods, Distribution
objects also implement all
of the IResourceProvider and IMetadataProvider Methods (which are
documented in later sections):
has_metadata(name)
metadata_isdir(name)
metadata_listdir(name)
get_metadata(name)
get_metadata_lines(name)
run_script(script_name, namespace)
get_resource_filename(manager, resource_name)
get_resource_stream(manager, resource_name)
get_resource_string(manager, resource_name)
has_resource(resource_name)
resource_isdir(resource_name)
resource_listdir(resource_name)
If the distribution was created with a metadata
argument, these resource and
metadata access methods are all delegated to that metadata
provider.
Otherwise, they are delegated to an EmptyProvider
, so that the distribution
will appear to have no resources or metadata. This delegation approach is used
so that supporting custom importers or new distribution formats can be done
simply by creating an appropriate IResourceProvider implementation; see the
section below on Supporting Custom Importers for more details.
ResourceManager
API¶
The ResourceManager
class provides uniform access to package resources,
whether those resources exist as files and directories or are compressed in
an archive of some kind.
Normally, you do not need to create or explicitly manage ResourceManager
instances, as the pkg_resources
module creates a global instance for you,
and makes most of its methods available as top-level names in the
pkg_resources
module namespace. So, for example, this code actually
calls the resource_string()
method of the global ResourceManager
:
import pkg_resources
my_data = pkg_resources.resource_string(__name__, "foo.dat")
Thus, you can use the APIs below without needing an explicit
ResourceManager
instance; just import and use them as needed.
Basic Resource Access¶
In the following methods, the package_or_requirement
argument may be either
a Python package/module name (e.g. foo.bar
) or a Requirement
instance.
If it is a package or module name, the named module or package must be
importable (i.e., be in a distribution or directory on sys.path
), and the
resource_name
argument is interpreted relative to the named package. (Note
that if a module name is used, then the resource name is relative to the
package immediately containing the named module. Also, you should not use use
a namespace package name, because a namespace package can be spread across
multiple distributions, and is therefore ambiguous as to which distribution
should be searched for the resource.)
If it is a Requirement
, then the requirement is automatically resolved
(searching the current Environment
if necessary) and a matching
distribution is added to the WorkingSet
and sys.path
if one was not
already present. (Unless the Requirement
can’t be satisfied, in which
case an exception is raised.) The resource_name
argument is then interpreted
relative to the root of the identified distribution; i.e. its first path
segment will be treated as a peer of the top-level modules or packages in the
distribution.
Note that resource names must be /
-separated paths rooted at the package,
cannot contain relative names like ".."
, and cannot be absolute. Do not use
os.path
routines to manipulate resource paths, as they are not filesystem
paths.
resource_exists(package_or_requirement, resource_name)
Does the named resource exist? Return
True
orFalse
accordingly.resource_stream(package_or_requirement, resource_name)
Return a readable file-like object for the specified resource; it may be an actual file, a
StringIO
, or some similar object. The stream is in “binary mode”, in the sense that whatever bytes are in the resource will be read as-is.resource_string(package_or_requirement, resource_name)
Return the specified resource as
bytes
. The resource is read in binary fashion, such that the returned string contains exactly the bytes that are stored in the resource.resource_isdir(package_or_requirement, resource_name)
Is the named resource a directory? Return
True
orFalse
accordingly.resource_listdir(package_or_requirement, resource_name)
List the contents of the named resource directory, just like
os.listdir
except that it works even if the resource is in a zipfile.
Note that only resource_exists()
and resource_isdir()
are insensitive
as to the resource type. You cannot use resource_listdir()
on a file
resource, and you can’t use resource_string()
or resource_stream()
on
directory resources. Using an inappropriate method for the resource type may
result in an exception or undefined behavior, depending on the platform and
distribution format involved.
Resource Extraction¶
resource_filename(package_or_requirement, resource_name)
Sometimes, it is not sufficient to access a resource in string or stream form, and a true filesystem filename is needed. In such cases, you can use this method (or module-level function) to obtain a filename for a resource. If the resource is in an archive distribution (such as a zipped egg), it will be extracted to a cache directory, and the filename within the cache will be returned. If the named resource is a directory, then all resources within that directory (including subdirectories) are also extracted. If the named resource is a C extension or “eager resource” (see the
setuptools
documentation for details), then all C extensions and eager resources are extracted at the same time.Archived resources are extracted to a cache location that can be managed by the following two methods:
set_extraction_path(path)
Set the base path where resources will be extracted to, if needed.
If you do not call this routine before any extractions take place, the path defaults to the return value of
get_default_cache()
. (Which is based on thePYTHON_EGG_CACHE
environment variable, with various platform-specific fallbacks. See that routine’s documentation for more details.)Resources are extracted to subdirectories of this path based upon information given by the resource provider. You may set this to a temporary directory, but then you must call
cleanup_resources()
to delete the extracted files when done. There is no guarantee thatcleanup_resources()
will be able to remove all extracted files. (On Windows, for example, you can’t unlink .pyd or .dll files that are still in use.)Note that you may not change the extraction path for a given resource manager once resources have been extracted, unless you first call
cleanup_resources()
.cleanup_resources(force=False)
Delete all extracted resource files and directories, returning a list of the file and directory names that could not be successfully removed. This function does not have any concurrency protection, so it should generally only be called when the extraction path is a temporary directory exclusive to a single process. This method is not automatically called; you must call it explicitly or register it as an
atexit
function if you wish to ensure cleanup of a temporary directory used for extractions.
“Provider” Interface¶
If you are implementing an IResourceProvider
and/or IMetadataProvider
for a new distribution archive format, you may need to use the following
IResourceManager
methods to coordinate extraction of resources to the
filesystem. If you’re not implementing an archive format, however, you have
no need to use these methods. Unlike the other methods listed above, they are
not available as top-level functions tied to the global ResourceManager
;
you must therefore have an explicit ResourceManager
instance to use them.
get_cache_path(archive_name, names=())
Return absolute location in cache for
archive_name
andnames
The parent directory of the resulting path will be created if it does not already exist.
archive_name
should be the base filename of the enclosing egg (which may not be the name of the enclosing zipfile!), including its “.egg” extension.names
, if provided, should be a sequence of path name parts “under” the egg’s extraction location.This method should only be called by resource providers that need to obtain an extraction location, and only for names they intend to extract, as it tracks the generated names for possible cleanup later.
extraction_error()
Raise an
ExtractionError
describing the active exception as interfering with the extraction process. You should call this if you encounter any OS errors extracting the file to the cache path; it will format the operating system exception for you, and add other information to theExtractionError
instance that may be needed by programs that want to wrap or handle extraction errors themselves.postprocess(tempname, filename)
Perform any platform-specific postprocessing of
tempname
. Resource providers should call this method ONLY after successfully extracting a compressed resource. They must NOT call it on resources that are already in the filesystem.tempname
is the current (temporary) name of the file, andfilename
is the name it will be renamed to by the caller after this routine returns.
Metadata API¶
The metadata API is used to access metadata resources bundled in a pluggable
distribution. Metadata resources are virtual files or directories containing
information about the distribution, such as might be used by an extensible
application or framework to connect “plugins”. Like other kinds of resources,
metadata resource names are /
-separated and should not contain ..
or
begin with a /
. You should not use os.path
routines to manipulate
resource paths.
The metadata API is provided by objects implementing the IMetadataProvider
or IResourceProvider
interfaces. Distribution
objects implement this
interface, as do objects returned by the get_provider()
function:
get_provider(package_or_requirement)
If a package name is supplied, return an
IResourceProvider
for the package. If aRequirement
is supplied, resolve it by returning aDistribution
from the current working set (searching the currentEnvironment
if necessary and adding the newly foundDistribution
to the working set). If the named package can’t be imported, or theRequirement
can’t be satisfied, an exception is raised.NOTE: if you use a package name rather than a
Requirement
, the object you get back may not be a pluggable distribution, depending on the method by which the package was installed. In particular, “development” packages and “single-version externally-managed” packages do not have any way to map from a package name to the corresponding project’s metadata. Do not write code that passes a package name toget_provider()
and then tries to retrieve project metadata from the returned object. It may appear to work when the named package is in an.egg
file or directory, but it will fail in other installation scenarios. If you want project metadata, you need to ask for a project, not a package.
IMetadataProvider
Methods¶
The methods provided by objects (such as Distribution
instances) that
implement the IMetadataProvider
or IResourceProvider
interfaces are:
has_metadata(name)
Does the named metadata resource exist?
metadata_isdir(name)
Is the named metadata resource a directory?
metadata_listdir(name)
List of metadata names in the directory (like
os.listdir()
)get_metadata(name)
Return the named metadata resource as a string. The data is read in binary mode; i.e., the exact bytes of the resource file are returned.
get_metadata_lines(name)
Yield named metadata resource as list of non-blank non-comment lines. This is short for calling
yield_lines(provider.get_metadata(name))
. See the section on yield_lines() below for more information on the syntax it recognizes.run_script(script_name, namespace)
Execute the named script in the supplied namespace dictionary. Raises
ResolutionError
if there is no script by that name in thescripts
metadata directory.namespace
should be a Python dictionary, usually a module dictionary if the script is being run as a module.
Exceptions¶
pkg_resources
provides a simple exception hierarchy for problems that may
occur when processing requests to locate and activate packages:
ResolutionError
DistributionNotFound
VersionConflict
UnknownExtra
ExtractionError
ResolutionError
This class is used as a base class for the other three exceptions, so that you can catch all of them with a single “except” clause. It is also raised directly for miscellaneous requirement-resolution problems like trying to run a script that doesn’t exist in the distribution it was requested from.
DistributionNotFound
A distribution needed to fulfill a requirement could not be found.
VersionConflict
The requested version of a project conflicts with an already-activated version of the same project.
UnknownExtra
One of the “extras” requested was not recognized by the distribution it was requested from.
ExtractionError
A problem occurred extracting a resource to the Python Egg cache. The following attributes are available on instances of this exception:
- manager
The resource manager that raised this exception
- cache_path
The base directory for resource extraction
- original_error
The exception instance that caused extraction to fail
Supporting Custom Importers¶
By default, pkg_resources
supports normal filesystem imports, and
zipimport
importers. If you wish to use the pkg_resources
features
with other (PEP 302-compatible) importers or module loaders, you may need to
register various handlers and support functions using these APIs:
register_finder(importer_type, distribution_finder)
Register
distribution_finder
to find distributions insys.path
items.importer_type
is the type or class of a PEP 302 “Importer” (sys.path
item handler), anddistribution_finder
is a callable that, when passed a path item, the importer instance, and anonly
flag, yieldsDistribution
instances found under that path item. (Theonly
flag, if true, means the finder should yield onlyDistribution
objects whoselocation
is equal to the path item provided.)See the source of the
pkg_resources.find_on_path
function for an example finder function.register_loader_type(loader_type, provider_factory)
Register
provider_factory
to makeIResourceProvider
objects forloader_type
.loader_type
is the type or class of a PEP 302module.__loader__
, andprovider_factory
is a function that, when passed a module object, returns an IResourceProvider for that module, allowing it to be used with the ResourceManager API.register_namespace_handler(importer_type, namespace_handler)
Register
namespace_handler
to declare namespace packages for the givenimporter_type
.importer_type
is the type or class of a PEP 302 “importer” (sys.path item handler), andnamespace_handler
is a callable with a signature like this:def namespace_handler(importer, path_entry, moduleName, module): # return a path_entry to use for child packages
Namespace handlers are only called if the relevant importer object has already agreed that it can handle the relevant path item. The handler should only return a subpath if the module
__path__
does not already contain an equivalent subpath. Otherwise, it should return None.For an example namespace handler, see the source of the
pkg_resources.file_ns_handler
function, which is used for both zipfile importing and regular importing.
IResourceProvider¶
IResourceProvider
is an abstract class that documents what methods are
required of objects returned by a provider_factory
registered with
register_loader_type()
. IResourceProvider
is a subclass of
IMetadataProvider
, so objects that implement this interface must also
implement all of the IMetadataProvider Methods as well as the methods
shown here. The manager
argument to the methods below must be an object
that supports the full ResourceManager API documented above.
get_resource_filename(manager, resource_name)
Return a true filesystem path for
resource_name
, coordinating the extraction withmanager
, if the resource must be unpacked to the filesystem.get_resource_stream(manager, resource_name)
Return a readable file-like object for
resource_name
.get_resource_string(manager, resource_name)
Return a string containing the contents of
resource_name
.has_resource(resource_name)
Does the package contain the named resource?
resource_isdir(resource_name)
Is the named resource a directory? Return a false value if the resource does not exist or is not a directory.
resource_listdir(resource_name)
Return a list of the contents of the resource directory, ala
os.listdir()
. Requesting the contents of a non-existent directory may raise an exception.
Note, by the way, that your provider classes need not (and should not) subclass
IResourceProvider
or IMetadataProvider
! These classes exist solely
for documentation purposes and do not provide any useful implementation code.
You may instead wish to subclass one of the built-in resource providers.
Built-in Resource Providers¶
pkg_resources
includes several provider classes that are automatically used
where appropriate. Their inheritance tree looks like this:
NullProvider
EggProvider
DefaultProvider
PathMetadata
ZipProvider
EggMetadata
EmptyProvider
FileMetadata
NullProvider
This provider class is just an abstract base that provides for common provider behaviors (such as running scripts), given a definition for just a few abstract methods.
EggProvider
This provider class adds in some egg-specific features that are common to zipped and unzipped eggs.
DefaultProvider
This provider class is used for unpacked eggs and “plain old Python” filesystem modules.
ZipProvider
This provider class is used for all zipped modules, whether they are eggs or not.
EmptyProvider
This provider class always returns answers consistent with a provider that has no metadata or resources.
Distribution
objects created without ametadata
argument use an instance of this provider class instead. Since allEmptyProvider
instances are equivalent, there is no need to have more than one instance.pkg_resources
therefore creates a global instance of this class under the nameempty_provider
, and you may use it if you have need of anEmptyProvider
instance.PathMetadata(path, egg_info)
Create an
IResourceProvider
for a filesystem-based distribution, wherepath
is the filesystem location of the importable modules, andegg_info
is the filesystem location of the distribution’s metadata directory.egg_info
should usually be theEGG-INFO
subdirectory ofpath
for an “unpacked egg”, and aProjectName.egg-info
subdirectory ofpath
for a “development egg”. However, other uses are possible for custom purposes.EggMetadata(zipimporter)
Create an
IResourceProvider
for a zipfile-based distribution. Thezipimporter
should be azipimport.zipimporter
instance, and may represent a “basket” (a zipfile containing multiple “.egg” subdirectories) a specific egg within a basket, or a zipfile egg (where the zipfile itself is a “.egg”). It can also be a combination, such as a zipfile egg that also contains other eggs.FileMetadata(path_to_pkg_info)
Create an
IResourceProvider
that provides exactly one metadata resource:PKG-INFO
. The supplied path should be a distutils PKG-INFO file. This is basically the same as anEmptyProvider
, except that requests forPKG-INFO
will be answered using the contents of the designated file. (This provider is used to wrap.egg-info
files installed by vendor-supplied system packages.)
Utility Functions¶
In addition to its high-level APIs, pkg_resources
also includes several
generally-useful utility routines. These routines are used to implement the
high-level APIs, but can also be quite useful by themselves.
Parsing Utilities¶
parse_version(version)
Parsed a project’s version string as defined by PEP 440. The returned value will be an object that represents the version. These objects may be compared to each other and sorted. The sorting algorithm is as defined by PEP 440 with the addition that any version which is not a valid PEP 440 version will be considered less than any valid PEP 440 version and the invalid versions will continue sorting using the original algorithm.
yield_lines(strs)
Yield non-empty/non-comment lines from a string/unicode or a possibly-nested sequence thereof. If
strs
is an instance ofbasestring
, it is split into lines, and each non-blank, non-comment line is yielded after stripping leading and trailing whitespace. (Lines whose first non-blank character is#
are considered comment lines.)If
strs
is not an instance ofbasestring
, it is iterated over, and each item is passed recursively toyield_lines()
, so that an arbitrarily nested sequence of strings, or sequences of sequences of strings can be flattened out to the lines contained therein. So for example, passing a file object or a list of strings toyield_lines
will both work. (Note that between each string in a sequence of strings there is assumed to be an implicit line break, so lines cannot bridge two strings in a sequence.)This routine is used extensively by
pkg_resources
to parse metadata and file formats of various kinds, and most otherpkg_resources
parsing functions that yield multiple values will use it to break up their input. However, this routine is idempotent, so callingyield_lines()
on the output of another call toyield_lines()
is completely harmless.split_sections(strs)
Split a string (or possibly-nested iterable thereof), yielding
(section, content)
pairs found using an.ini
-like syntax. Eachsection
is a whitespace-stripped version of the section name (”[section]
”) and eachcontent
is a list of stripped lines excluding blank lines and comment-only lines. If there are any non-blank, non-comment lines before the first section header, they’re yielded in a firstsection
ofNone
.This routine uses
yield_lines()
as its front end, so you can pass in anything thatyield_lines()
accepts, such as an open text file, string, or sequence of strings.ValueError
is raised if a malformed section header is found (i.e. a line starting with[
but not ending with]
).Note that this simplistic parser assumes that any line whose first nonblank character is
[
is a section heading, so it can’t support .ini format variations that allow[
as the first nonblank character on other lines.safe_name(name)
Return a “safe” form of a project’s name, suitable for use in a
Requirement
string, as a distribution name, or a PyPI project name. All non-alphanumeric runs are condensed to single “-” characters, such that a name like “The $$$ Tree” becomes “The-Tree”. Note that if you are generating a filename from this value you should combine it with a call toto_filename()
so all dashes (“-”) are replaced by underscores (“_”). Seeto_filename()
.safe_version(version)
This will return the normalized form of any PEP 440 version. If the version string is not PEP 440 compatible, this function behaves similar to
safe_name()
except that spaces in the input become dots, and dots are allowed to exist in the output. As withsafe_name()
, if you are generating a filename from this you should replace any “-” characters in the output with underscores.safe_extra(extra)
Return a “safe” form of an extra’s name, suitable for use in a requirement string or a setup script’s
extras_require
keyword. This routine is similar tosafe_name()
except that non-alphanumeric runs are replaced by a single underbar (_
), and the result is lowercased.to_filename(name_or_version)
Escape a name or version string so it can be used in a dash-separated filename (or
#egg=name-version
tag) without ambiguity. You should only pass in values that were returned bysafe_name()
orsafe_version()
.
Platform Utilities¶
get_build_platform()
Return this platform’s identifier string. For Windows, the return value is
"win32"
, and for macOS it is a string of the form"macosx-10.4-ppc"
. All other platforms return the same uname-based string that thedistutils.util.get_platform()
function returns. This string is the minimum platform version required by distributions built on the local machine. (Backward compatibility note: setuptools versions prior to 0.6b1 called this functionget_platform()
, and the function is still available under that name for backward compatibility reasons.)get_supported_platform()
(New in 0.6b1)This is the similar to
get_build_platform()
, but is the maximum platform version that the local machine supports. You will usually want to use this value as theprovided
argument to thecompatible_platforms()
function.compatible_platforms(provided, required)
Return true if a distribution built on the
provided
platform may be used on therequired
platform. If either platform value isNone
, it is considered a wildcard, and the platforms are therefore compatible. Likewise, if the platform strings are equal, they’re also considered compatible, andTrue
is returned. Currently, the only non-equal platform strings that are considered compatible are macOS platform strings with the same hardware type (e.g.ppc
) and major version (e.g.10
) with theprovided
platform’s minor version being less than or equal to therequired
platform’s minor version.get_default_cache()
Determine the default cache location for extracting resources from zipped eggs. This routine returns the
PYTHON_EGG_CACHE
environment variable, if set. Otherwise, on Windows, it returns a “Python-Eggs” subdirectory of the user’s “Application Data” directory. On all other systems, it returnsos.path.expanduser("~/.python-eggs")
ifPYTHON_EGG_CACHE
is not set.
PEP 302 Utilities¶
get_importer(path_item)
A deprecated alias for
pkgutil.get_importer()
File/Path Utilities¶
ensure_directory(path)
Ensure that the parent directory (
os.path.dirname
) ofpath
actually exists, usingos.makedirs()
if necessary.normalize_path(path)
Return a “normalized” version of
path
, such that two paths represent the same filesystem location if they have equalnormalized_path()
values. Specifically, this is a shortcut for callingos.path.realpath
andos.path.normcase
onpath
. Unfortunately, on certain platforms (notably Cygwin and macOS) thenormcase
function does not accurately reflect the platform’s case-sensitivity, so there is always the possibility of two apparently-different paths being equal on such platforms.
History¶
- 0.6c9
Fix
resource_listdir('')
always returning an empty list for zipped eggs.
- 0.6c7
Fix package precedence problem where single-version eggs installed in
site-packages
would take precedence over.egg
files (or directories) installed insite-packages
.
- 0.6c6
Fix extracted C extensions not having executable permissions under Cygwin.
Allow
.egg-link
files to contain relative paths.Fix cache dir defaults on Windows when multiple environment vars are needed to construct a path.
- 0.6c4
Fix “dev” versions being considered newer than release candidates.
- 0.6c3
Python 2.5 compatibility fixes.
- 0.6c2
Fix a problem with eggs specified directly on
PYTHONPATH
on case-insensitive filesystems possibly not showing up in the default working set, due to differing normalizations ofsys.path
entries.
- 0.6b3
Fixed a duplicate path insertion problem on case-insensitive filesystems.
- 0.6b1
Split
get_platform()
intoget_supported_platform()
andget_build_platform()
to work around a Mac versioning problem that caused the behavior ofcompatible_platforms()
to be platform specific.Fix entry point parsing when a standalone module name has whitespace between it and the extras.
- 0.6a11
Added
ExtractionError
andResourceManager.extraction_error()
so that cache permission problems get a more user-friendly explanation of the problem, and so that programs can catch and handle extraction errors if they need to.
- 0.6a10
Added the
extras
attribute toDistribution
, thefind_plugins()
method toWorkingSet
, and the__add__()
and__iadd__()
methods toEnvironment
.safe_name()
now allows dots in project names.There is a new
to_filename()
function that escapes project names and versions for safe use in constructing egg filenames from a Distribution object’s metadata.Added
Distribution.clone()
method, and keyword argument support to otherDistribution
constructors.Added the
DEVELOP_DIST
precedence, and automatically assign it to eggs using.egg-info
format.
- 0.6a9
Don’t raise an error when an invalid (unfinished) distribution is found unless absolutely necessary. Warn about skipping invalid/unfinished eggs when building an Environment.
Added support for
.egg-info
files or directories with version/platform information embedded in the filename, so that system packagers have the option of includingPKG-INFO
files to indicate the presence of a system-installed egg, without needing to use.egg
directories, zipfiles, or.pth
manipulation.Changed
parse_version()
to remove dashes before pre-release tags, so that0.2-rc1
is considered an older version than0.2
, and is equal to0.2rc1
. The idea that a dash always meant a post-release version was highly non-intuitive to setuptools users and Python developers, who seem to want to use-rc
version numbers a lot.
- 0.6a8
Fixed a problem with
WorkingSet.resolve()
that prevented version conflicts from being detected at runtime.Improved runtime conflict warning message to identify a line in the user’s program, rather than flagging the
warn()
call inpkg_resources
.Avoid giving runtime conflict warnings for namespace packages, even if they were declared by a different package than the one currently being activated.
Fix path insertion algorithm for case-insensitive filesystems.
Fixed a problem with nested namespace packages (e.g.
peak.util
) not being set as an attribute of their parent package.
- 0.6a6
Activated distributions are now inserted in
sys.path
(and the working set) just before the directory that contains them, instead of at the end. This allows e.g. eggs insite-packages
to override unmanaged modules in the same location, and allows eggs found earlier onsys.path
to override ones found later.When a distribution is activated, it now checks whether any contained non-namespace modules have already been imported and issues a warning if a conflicting module has already been imported.
Changed dependency processing so that it’s breadth-first, allowing a depender’s preferences to override those of a dependee, to prevent conflicts when a lower version is acceptable to the dependee, but not the depender.
Fixed a problem extracting zipped files on Windows, when the egg in question has had changed contents but still has the same version number.
- 0.6a4
Fix a bug in
WorkingSet.resolve()
that was introduced in 0.6a3.
- 0.6a3
Added
safe_extra()
parsing utility routine, and use it for Requirement, EntryPoint, and Distribution objects’ extras handling.
- 0.6a1
Enhanced performance of
require()
and related operations when all requirements are already in the working set, and enhanced performance of directory scanning for distributions.Fixed some problems using
pkg_resources
w/PEP 302 loaders other thanzipimport
, and the previously-broken “eager resource” support.Fixed
pkg_resources.resource_exists()
not working correctly, along with some other resource API bugs.Many API changes and enhancements:
Added
EntryPoint
,get_entry_map
,load_entry_point
, andget_entry_info
APIs for dynamic plugin discovery.list_resources
is nowresource_listdir
(and it actually works)Resource API functions like
resource_string()
that accepted a package name and resource name, will now also accept aRequirement
object in place of the package name (to allow access to non-package data files in an egg).get_provider()
will now accept aRequirement
instance or a module name. If it is given aRequirement
, it will return a correspondingDistribution
(by callingrequire()
if a suitable distribution isn’t already in the working set), rather than returning a metadata and resource provider for a specific module. (The difference is in how resource paths are interpreted; supplying a module name means resources path will be module-relative, rather than relative to the distribution’s root.)Distribution
objects now implement theIResourceProvider
andIMetadataProvider
interfaces, so you don’t need to reference the (no longer available)metadata
attribute to get at these interfaces.Distribution
andRequirement
both have aproject_name
attribute for the project name they refer to. (Previously these werename
anddistname
attributes.)The
path
attribute ofDistribution
objects is nowlocation
, because it isn’t necessarily a filesystem path (and hasn’t been for some time now). Thelocation
ofDistribution
objects in the filesystem should always be normalized usingpkg_resources.normalize_path()
; all of the setuptools’ code that generates distributions from the filesystem (includingDistribution.from_filename()
) ensure this invariant, but if you use a more generic API likeDistribution()
orDistribution.from_location()
you should take care that you don’t create a distribution with an un-normalized filesystem path.Distribution
objects now have anas_requirement()
method that returns aRequirement
for the distribution’s project name and version.Distribution objects no longer have an
installed_on()
method, and theinstall_on()
method is nowactivate()
(but may go away altogether soon). Thedepends()
method has also been renamed torequires()
, andInvalidOption
is nowUnknownExtra
.find_distributions()
now takes an additional argument calledonly
, that tells it to only yield distributions whose location is the passed-in path. (It defaults to False, so that the default behavior is unchanged.)AvailableDistributions
is now calledEnvironment
, and theget()
,__len__()
, and__contains__()
methods were removed, because they weren’t particularly useful.__getitem__()
no longer raisesKeyError
; it just returns an empty list if there are no distributions for the named project.The
resolve()
method ofEnvironment
is now a method ofWorkingSet
instead, and thebest_match()
method now uses a working set instead of a path list as its second argument.There is a new
pkg_resources.add_activation_listener()
API that lets you register a callback for notifications about distributions added tosys.path
(including the distributions already on it). This is basically a hook for extensible applications and frameworks to be able to search for plugin metadata in distributions added at runtime.
- 0.5a13
Fixed a bug in resource extraction from nested packages in a zipped egg.
- 0.5a12
Updated extraction/cache mechanism for zipped resources to avoid inter-process and inter-thread races during extraction. The default cache location can now be set via the
PYTHON_EGGS_CACHE
environment variable, and the default Windows cache is now aPython-Eggs
subdirectory of the current user’s “Application Data” directory, if thePYTHON_EGGS_CACHE
variable isn’t set.
- 0.5a10
Fix a problem with
pkg_resources
being confused by non-existent eggs onsys.path
(e.g. if a user deletes an egg without removing it from theeasy-install.pth
file).Fix a problem with “basket” support in
pkg_resources
, where egg-finding never actually went inside.egg
files.Made
pkg_resources
import the module you request resources from, if it’s not already imported.
- 0.5a4
pkg_resources.AvailableDistributions.resolve()
and related methods now accept aninstaller
argument: a callable taking one argument, aRequirement
instance. The callable must return aDistribution
object, orNone
if no distribution is found. This feature is used by EasyInstall to resolve dependencies by recursively invoking itself.
- 0.4a4
Fix problems with
resource_listdir()
,resource_isdir()
and resource directory extraction for zipped eggs.
- 0.4a3
Fixed scripts not being able to see a
__file__
variable in__main__
Fixed a problem with
resource_isdir()
implementation that was introduced in 0.4a2.
- 0.4a1
Fixed a bug in requirements processing for exact versions (i.e.
==
and!=
) when only one condition was included.Added
safe_name()
andsafe_version()
APIs to clean up handling of arbitrary distribution names and versions found on PyPI.
- 0.3a4
pkg_resources
now supports resource directories, not just the resources in them. In particular, there areresource_listdir()
andresource_isdir()
APIs.pkg_resources
now supports “egg baskets” – .egg zipfiles which contain multiple distributions in subdirectories whose names end with.egg
. Having such a “basket” in a directory onsys.path
is equivalent to having the individual eggs in that directory, but the contained eggs can be individually added (or not) tosys.path
. Currently, however, there is no automated way to create baskets.Namespace package manipulation is now protected by the Python import lock.
- 0.3a1
Initial release.