zip_safe flag is a
setuptools configuration mainly associated
egg distribution format
(which got replaced in the ecosystem by the newer
wheel format) and the
easy_install command (deprecated in
It is very unlikely that the values of
zip_safe will affect modern
deployments that use pip for installing packages.
Moreover, new users of
setuptools should not attempt to create egg files
using the deprecated
Therefore, this flag is considered obsolete.
This document, however, describes what was the historical motivation behind this flag, and how it was used.
For some use cases (such as bundling as part of a larger application), Python packages may be run directly from a zip file. Not all packages, however, are capable of running in compressed form, because they may expect to be able to access either source code or data files as normal operating system files.
In the past,
setuptools would install a project distributed
as a zipfile or a directory (via the
easy_install command or
python setup.py install),
the default choice being determined by the project’s
zip_safe flag was used?#
To set this flag, a developer would pass a boolean value for the
zip_safe argument to the
setup() function, or omit it. When omitted, the
command would analyze the project’s contents to see if it could detect any
conditions that preventing the project from working in a zipfile.
This was extremely conservative:
bdist_egg would consider the
project unsafe if it contained any C extensions or datafiles whatsoever. This
does not mean that the project couldn’t or wouldn’t work as a zipfile! It just
means that the
bdist_egg authors were not yet comfortable asserting that
the project would work. If the project did not contain any C or data files, and did not
attempt to perform
__path__ introspection or source code manipulation, then
there was an extremely solid chance the project will work when installed as a
zipfile. (And if the project used
pkg_resources for all its data file
access, then C extensions and other data files shouldn’t be a problem at all.
See the Accessing Data Files at Runtime section for more information.)
The developer could manually set
True to perform tests,
or to override the default behaviour (after checking all the warnings and
understanding the implications), this would allow
setuptools to install the
project as a zip file. Alternatively, by setting
developers could force
setuptools to always install the project as a
Modern ways of loading packages from zip files#
Currently, popular Python package installers (such as pip) and package
indexes (such as PyPI) consider that distribution packages are always
installed as a directory.
It is however still possible to load packages from zip files added to
sys.path, thanks to the
importlib machinery provided by Python standard library.
When working with modules loaded from a zip file, it is important to keep in
mind that values of
__path__ might not work as expected.
Please check the documentation for
importlib.resources, if file
locations are important for your use case.