def _opt_call_from_base_type(self, value):
if isinstance(value, _BaseValue):<EOL><INDENT>value = self._call_from_base_type(value.b_val)<EOL><DEDENT>return value<EOL>
Call _from_base_type() if necessary.

        If the value is a _BaseValue instance, unwrap it and call all
        _from_base_type() methods.  Otherwise, return the value
        unchanged.