'Return the key associated to a registered file object.
Returns:
SelectorKey for this file object'

def get_key(self, fileobj):

    mapping = self.get_map()
    if (mapping is None):
        raise RuntimeError('Selector    is    closed')
    try:
        return mapping[fileobj]
    except KeyError:
        raise KeyError('{0!r}    is    not    registered'.format(fileobj))
