the _version.py file is autogenerated at build time from git tag using setuptools_scm; the pyclipper.__version__ variable exports that, as it's common in python packaging. This allows clients to import pyclipper and check its __version__ without needing to query the package metadata (which may be missing when pyclipper is embedded in native applications).
setuptools_scm is a setuptools plugin that uses git metadata to manage python package versions
https://github.com/pypa/setuptools_scm
It also replaces the use of MANIFEST.in, by including in the soruce distribution all the
files that are under version control (using `git ls-files`).
An extra plugin 'setuptools_scm_git_archive' also adds support for git archives,
e.g the .zip files automatically generated on Github.
https://github.com/Changaco/setuptools_scm_git_archive
For example, one could do: `pip install https://github.com/greginvm/pyclipper/archive/1.0.4.zip`
Note that installing from git archives currently works only for tagged commits, because
of limitations of git archive format itself.
However, for non-tagged commits one can still install from the git repo:
`pip install git+https://github.com/greginvm/pyclipper`
