'Creates :py:class:viz.BaseViz object from the url_params_multidict.
:param werkzeug.datastructures.MultiDict url_params_multidict:
Contains the visualization params, they override the self.params
stored in the database
:return: object of the \'viz_type\' type that is taken from the
url_params_multidict or self.params.
:rtype: :py:class:viz.BaseViz'

def get_viz(self, url_params_multidict=None):

    slice_params = json.loads(self.params)
    slice_params[u'slice_id'] = self.id
    slice_params[u'json'] = u'false'
    slice_params[u'slice_name'] = self.slice_name
    slice_params[u'viz_type'] = (self.viz_type if self.viz_type else u'table')
    return viz_types[slice_params.get(u'viz_type')](self.datasource, form_data=slice_params)
