def __iadd__(self, other):
        """In-place addition of a distribution or environment"""
        if isinstance(other, Distribution):
            self.add(other)
        elif isinstance(other, Environment):
            for project in other:
                for dist in other[project]:
                    self.add(dist)
        else:
            raise TypeError("Can't add %r to environment" % (other,))
        return self
In-place addition of a distribution or environment
product/gradle-plugin/src/main/python/pip/_vendor/pkg_resources/__init__.py