def markers_pass(self, req, extras=None):
        """
        Evaluate markers for req against each extra that
        demanded it.

        Return False if the req has a marker and fails
        evaluation. Otherwise, return True.
        """
        extra_evals = (
            req.marker.evaluate({'extra': extra})
            for extra in self.get(req, ()) + (extras or (None,))
        )
        return not req.marker or any(extra_evals)

        Evaluate markers for req against each extra that
        demanded it.

        Return False if the req has a marker and fails
        evaluation. Otherwise, return True.
        
stackoverflow/venv/lib/python3.6/site-packages/pip-19.0.3-py3.6.egg/pip/_vendor/pkg_resources/__init__.py