'Modify the filename of a log file when rotating.
This is provided so that a custom filename can be provided.
The default implementation calls the \'namer\' attribute of the
handler, if it\'s callable, passing the default name to
it. If the attribute isn\'t callable (the default is None), the name
is returned unchanged.
:param default_name: The default name for the log file.'

def rotation_filename(self, default_name):

    if (not callable(self.namer)):
        result = default_name
    else:
        result = self.namer(default_name)
    return result
