I have this virtual method in TpBaseProtocolClass:

  gchar *(*normalize_contact) (TpBaseProtocol *self,
      const gchar *contact,
      GError **error);

which translates to this g-i:

      <virtual-method name="normalize_contact" throws="1">
        <return-value transfer-ownership="full">
          <type name="utf8" c:type="gchar*"/>
        </return-value>
        <parameters>
          <instance-parameter name="self" transfer-ownership="none">
            <type name="BaseProtocol" c:type="TpBaseProtocol*"/>
          </instance-parameter>
          <parameter name="contact" transfer-ownership="none">
            <type name="utf8" c:type="const gchar*"/>
          </parameter>
        </parameters>
      </virtual-method>

I would like to be able to do this:

    def do_normalize_contact(self, contact):
        if contact:
            return contact.lower()
        else:
            raise ValueError('The empty string is not a valid identifier')

or ideally, something more like this:

    def do_normalize_contact(self, contact):
        if contact:
            return contact.lower()
        else:
            raise TelepathyGLib.Error(TelepathyGLib.Error.INVALID_HANDLE,
                'The empty string is not a valid identifier')

This doesn't seem to be possible: if I raise an exception, it just gets printed to stderr:

> Traceback (most recent call last):
>   File "tests/python/cm.py", line 40, in do_normalize_contact
>     raise ValueError('Invalid identifier')
> ValueError: Invalid identifier

and then my Python code returns None from the vfunc without setting the GError correctly:

** (process:19507): CRITICAL **: dbus_g_method_return_error: assertion `error != NULL' failed