Why There is No Source Distribution of PyGamma on PyPI
A source distribution of a package is created with
python setup.py sdist. It creates a tarball (or zip file on Windows) that contains files that one can download and unpack, and then run
python setup.py install.
Source distributions make a lot of sense for pure Python packages, or for packages that can be compiled easily on their target platform(s). PyGamma is a different animal. It's principally C++ code, and that code can only be compiled with our special build process. A source distribution wouldn't do anyone any good.
We could provide the Python source + prebuilt binaries for each platform as a source distribution. That's possible, but would require some care to create.
If someone really wants to build and install from source, they can get the code from our public repository.