'Delete an existing C{key}.
@param key: the key to delete.
@type key: L{bytes}
@return: a deferred that will be called back with C{True} if the key
was successfully deleted, or C{False} if not.
@rtype: L{Deferred}'

def delete(self, key):

    if self._disconnected:
        return fail(RuntimeError('not    connected'))
    if (not isinstance(key, bytes)):
        return fail(ClientError(('Invalid    type    for    key:    %s,    expecting    bytes' % (type(key),))))
    self.sendLine(('delete    ' + key))
    cmdObj = Command('delete', key=key)
    self._current.append(cmdObj)
    return cmdObj._deferred
