req_install.py 文件源码

def setup_py(self):
        assert self.source_dir, "No source dir for %s" % self
        try:
            import setuptools  # noqa
        except ImportError:
            if get_installed_version('setuptools') is None:
                add_msg = "Please install setuptools."
            else:
                add_msg = traceback.format_exc()
            # Setuptools is not available
            raise InstallationError(
                "Could not import setuptools which is required to "
                "install from a source distribution.\n%s" % add_msg
            )

        setup_py = os.path.join(self.setup_py_dir, 'setup.py')

        # Python2 __file__ should not be unicode
        if six.PY2 and isinstance(setup_py, six.text_type):
            setup_py = setup_py.encode(sys.getfilesystemencoding())

        return setup_py