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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 start(cmd, port=None, numRetries=10, label="default"):
 """ Start a sumo server using cmd, establish a connection to it and store it under the given label. This method is not thread-safe. """

    if port is None:
        port = sumolib.miscutils.getFreeSocketPort()
    sumoProcess = subprocess.Popen(cmd + ["--remote-port", str(port)])
    _connections[label] = connect(port, numRetries, "localhost", sumoProcess)
    switch(label)
    return getVersion()