'Send a part message.
@type who: C{str} or C{unicode}
@param who: The name of the user joining.  Should be of the form
username!ident@hostmask (unless you know better!).
@type where: C{str} or C{unicode}
@param where: The channel the user is joining.
@type reason: C{str} or C{unicode}
@param reason: A string describing the misery which caused this poor
soul to depart.'

def part(self, who, where, reason=None):

    if reason:
        self.sendLine((':%s    PART    %s    :%s' % (who, where, reason)))
    else:
        self.sendLine((':%s    PART    %s' % (who, where)))
