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When creating a setup.py for a new project, do you find yourself always writing the same block of code for parsing __version__ from your project's source? Something like this?

with open(join(dirname(__file__), 'package_name', '__init__.py')) as fp:
    for line in fp:
        m = re.search(r'^\s*__version__\s*=\s*([\'"])([^\'"]+)\1\s*$', line)
        if m:
            version = m.group(2)
            break
    else:
        raise RuntimeError('Unable to find own __version__ string')

setup(
    version = version,
    ...
)

Someone needs to put all that into a reusable package, am I right? Well, someone did, and this is that package.

Just use pip (You have pip, right?) to install read_version:

pip install read_version

1. Install read_version in your development environment.

2. Add a pyproject.toml file to your project declaring read_version as a build dependency. (This is needed so that other people can build your package from source; see PEP 518 for more information.) The contents of the file should look like:

   [build-system]
   requires = [
       "read_version ~= 0.1.0",
       "setuptools",
       "wheel"
   ]
   

3. In your setup.py, get rid of your boilerplate __version__-finding code and replace it with:

   from read_version import read_version
   
   setup(
       version = read_version('packagename', '__init__.py'),
       ...
   )
   

4. Done!

read_version exports a single function, also named read_version, whose signature is:

read_version(*filepath, variable='__version__', default=NOTHING)

read_version() takes one or more file path components pointing to a Python source file to parse. The path components will be joined together with os.path.join(), and then, if the path isn't absolute, the path to the directory containing the script calling read_version() will be prepended to the path. (No more join(dirname(__file__), ...) boilerplate needed!) read_version() then parses the given Python file and searches through the parse tree for any assignments to a variable named __version__, returning the last value assigned.

The variable keyword argument can be set to the name of a variable other than __version__ to search for assignments to a different variable instead.

If no assignments to the variable are found, a ValueError is raised. To instead return a default value when this happens, set the default keyword argument.

read_variable only finds assignments that occur at the top level of the module, outside of any blocks.

Only assignments of literal values are supported; assignments to __version__ involving more complicated expressions will cause an error to be raised.