def is_callable(self):
        """
        Ensures :attr:`subject` is a callable.
        """
        if not callable(self._subject):
            raise self._error_factory(_format("Expected {} to be callable", self._subject))
def is_callable ( self ) : if not callable ( self . _subject ) : raise self . _error_factory ( _format ( "Expected {} to be callable" , self . _subject ) )
Ensures :attr:`subject` is a callable.