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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 get_language():
 """Create or retrieve the parse tree for defining a sensor graph."""


    global sensor_graph, statement

    if sensor_graph is not None:
        return sensor_graph

    _create_primitives()
    _create_simple_statements()
    _create_block_bnf()

    sensor_graph = ZeroOrMore(statement) + StringEnd()
    sensor_graph.ignore(comment)

    return sensor_graph