We could not diagnose your build failure. If you are unable to proceed, please file an issue at http://www.github.com/grpc/grpc with `[Python install]` in the title; please attach the whole log (including everything that may have appeared above the Python backtrace).
    Traceback (most recent call last):
      File "/Volumes/BuildData/tmpfs/tmp/pip-req-build-__RJ3e/src/python/grpcio/commands.py", line 272, in build_extensions
        build_ext.build_ext.build_extensions(self)
      File "/Volumes/BuildData/tmpfs/src/github/grpc/workspace_python_macos_opt_gevent/py27_gevent/lib/python2.7/site-packages/Cython/Distutils/old_build_ext.py", line 194, in build_extensions
        self.build_extension(ext)
      File "/Volumes/BuildData/tmpfs/src/github/grpc/workspace_python_macos_opt_gevent/py27_gevent/lib/python2.7/site-packages/setuptools/command/build_ext.py", line 199, in build_extension
        _build_ext.build_extension(self, ext)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/command/build_ext.py", line 499, in build_extension
        depends=ext.depends)
      File "/Volumes/BuildData/tmpfs/tmp/pip-req-build-__RJ3e/src/python/grpcio/_parallel_compile_patch.py", line 43, in _parallel_compile
        output_dir, macros, include_dirs, sources, depends, extra_postargs)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/ccompiler.py", line 329, in _setup_compile
        raise TypeError, "'output_dir' must be a string or None"
    TypeError: 'output_dir' must be a string or None