提取给定PTable中所有的key Args: ptable (PTable): 输入PTable **options: 可配置选项 Returns: PCollection: 所有的key，以PCollection给出 >>> from bigflow import transforms >>> _p = _pipeline.parallelize({"A": [2, 3], "B": [4, 5]}) >>> transforms.extract_keys(_p).get() ["A"
(ptable, **options)
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