The py.exe launcher relies on manual quoting in the shebang line. That's the case for the shebang embedded in this pip executable. The problem is the "simple launcher" used by distlib 0.1.8. It always quotes the executable, even if it's already quoted. This is fixed in distlib 0.1.9, which should be updated in the next release of pip.

https://bitbucket.org/pypa/distlib/issue/47

As a workaround, you can use `python -m pip`.