looks like i hit this todo in `PythonRequirement`
...
# developmentf
full-kilobyte-93429
03/07/2016, 10:02 PMlooks like i hit this todo in
PythonRequirement Copy code
# TODO(pl): Change version_filter into a hashable flag instead of a lambda.
# It definitely belongs in the invalidation hash, and it's only ever used
# for differentiating between py3k and py2
self._version_filter = version_filter or (lambda py, pl: True)