def METHOD_NAME(self, key):
    """
        Retrieves a namespace from the dictionary
        Example:
        --------
        >>> from owslib.namespaces import Namespaces
        >>> ns = Namespaces()
        >>> ns.get_namespace('csw')
        'http://www.opengis.net/cat/csw/2.0.2'
        >>> ns.get_namespace('wfs20')
        'http://www.opengis.net/wfs/2.0'
    """
    retval = None
    if key in self.namespace_dict:
        retval = self.namespace_dict[key]
    return retval