'Leave a channel.
@type channel: C{str}
@param channel: The name of the channel to leave. If it has no prefix,
C{\'#\'} will be prepended to it.
@type reason: C{str}
@param reason: If given, the reason for leaving.'

def leave(self, channel, reason=None):

    if (channel[0] not in CHANNEL_PREFIXES):
        channel = ('#' + channel)
    if reason:
        self.sendLine(('PART    %s    :%s' % (channel, reason)))
    else:
        self.sendLine(('PART    %s' % (channel,)))
