# Automatic Resource Extraction#

In a modern setup, Python packages are usually installed as directories, and all the files can be found on deterministic locations on the disk. This means that most of the tools expect package resources to be “real” files.

There are a few occasions however that packages are loaded in a different way (e.g., from a zip file), which is incompatible with the assumptions mentioned above. Moreover, a package developer may also include non-extension native libraries or other files that C extensions may expect to be able to access.

In these scenarios, the use of importlib.resources is recommended.

Old implementations (prior to the advent of importlib.resources) and long-living projects, however, may still rely on the library pkg_resources to access these files.

If you have to support such systems, or want to provide backward compatibility for pkg_resources, you may need to add an special configuration to setuptools when packaging a project. This can be done by listing as eager_resources (argument to setup() in setup.py or field in setup.cfg) all the files that need to be extracted together, whenever a C extension in the project is imported.

This is especially important if your project includes shared libraries other than distutils/setuptools-built C extensions, and those shared libraries use file extensions other than .dll, .so, or .dylib, which are the extensions that setuptools 0.6a8 and higher automatically detects as shared libraries and adds to the native_libs.txt file for you. Any shared libraries whose names do not end with one of those extensions should be listed as eager_resources, because they need to be present in the filesystem when he C extensions that link to them are used.

The pkg_resources runtime for compressed packages will automatically extract all C extensions and eager_resources at the same time, whenever any C extension or eager resource is requested via the resource_filename() API. (C extensions are imported using resource_filename() internally.) This ensures that C extensions will see all of the “real” files that they expect to see.

Note also that you can list directory resource names in eager_resources as well, in which case the directory’s contents (including subdirectories) will be extracted whenever any C extension or eager resource is requested.

Please note that if you’re not sure whether you need to use this argument, you don’t! It’s really intended to support projects with lots of non-Python dependencies and as a last resort for crufty projects that can’t otherwise handle being compressed. If your package is pure Python, Python plus data files, or Python plus C, you really don’t need this. You’ve got to be using either C or an external program that needs “real” files in your project before there’s any possibility of eager_resources being relevant to your project.