'Get client ID given segment info
This is used by daemon to correctly cache widths for different clients
using a single renderer instance.
:param dict segment_info:
:ref:`Segment info dictionary <dev-segments-info>`. Out of it only
``client_id`` key is used. It is OK for this dictionary to not
contain this key.
:return: Any hashable value or ``None``.'

def get_client_id(self, segment_info):

    return (segment_info.get(u'client_id') if isinstance(segment_info, dict) else None)
