Return the WSDL version related to a WSDL namespace uri.

def WSDLUriToVersion(self, uri):
        """Return the WSDL version related to a WSDL namespace uri."""
        value = self._wsdl_uri_mapping.get(uri)
        if value is not None:
            return value
        raise ValueError(
            'Unsupported SOAP envelope uri: %s' % uri
            )