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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def publish(cls, message, client_filter=None):
 """Publish messages to subscribers. Args: message: The message to publish. client_filter: A filter function to call passing in each client. Only clients for whom the function returns True will have the message sent to them. """

    with cls._lock:
      for client in cls.subscribers:
        if (not client_filter) or client_filter(client):
          client.send(message)