find pip packages: pkg_resources specify custom target directory

Question

Is there any way to specify a custom target directory for pkg_resources to list pip packages? I want to be able to find packages which have been installed in a custom target directory using --target through something like pkg_resources.require() that already fed with a custom target directory.

What I don't want is to use:

• setuptools.find_packages as it's only using sys.path
• setuptools.PEP420PackageFinder.find
• Finding packages through traversing the directory names and files was not helping as well, as I need a more generic way of finding package namespaces.

I appreciate any help on this.

Answer 1

Update

Python 3.8 introduced importlib.metadata, a module for querying the installed packages that supersedes pkg_resources. Example usage:

In [1]: from importlib import metadata
In [2]: dists = metadata.distributions(path=['my_target_dir'])
In [3]: list(f"{d.metadata['Name']}=={d.metadata['Version']}" for d in dists)
Out[22]: 
['pip==20.0.2',
 'ipython==7.13.0',
 ...
]

For Python 2.7 and Python >=3.5, there's a backport called importlib-metadata:

$ pip install importlib-metadata

Original answer

The pkg_resources.find_distributions function (documented under Getting or Creating Distributions) accepts a target dir to search for packages in. Example:

$ ls -l my_target_dir/
total 36
drwxr-xr-x 2 hoefling hoefling 4096 May 17 13:29 __pycache__
-rw-r--r-- 1 hoefling hoefling  126 May 17 13:29 easy_install.py
drwxr-xr-x 5 hoefling hoefling 4096 May 17 13:29 pip
drwxr-xr-x 2 hoefling hoefling 4096 May 17 13:29 pip-10.0.1.dist-info
drwxr-xr-x 5 hoefling hoefling 4096 May 17 13:29 pkg_resources
drwxr-xr-x 6 hoefling hoefling 4096 May 17 13:29 setuptools
drwxr-xr-x 2 hoefling hoefling 4096 May 17 13:29 setuptools-39.1.0.dist-info
drwxr-xr-x 5 hoefling hoefling 4096 May 17 13:29 wheel
drwxr-xr-x 2 hoefling hoefling 4096 May 17 13:29 wheel-0.31.1.dist-info

Scanning my_target_dir with pkg_resources.find_distributions yields:

In [2]: list(pkg_resources.find_distributions('my_target_dir'))
Out[2]:
[wheel 0.31.1 (/data/gentoo64/tmp/so-50380624/my_target_dir),
 setuptools 39.1.0 (/data/gentoo64/tmp/so-50380624/my_target_dir),
 pip 10.0.1 (/data/gentoo64/tmp/so-50380624/my_target_dir)]