def __init__(self, size, period, offset=0):
    if size <= 0:
      raise ValueError('The size parameter must be strictly positive.')
    self.size = Duration.of(size)
    self.period = Duration.of(period)
    self.offset = Timestamp.of(offset) % size
dataset/ETHPy150Open GoogleCloudPlatform/DataflowPythonSDK/google/cloud/dataflow/transforms/window.py/SlidingWindows.__init__/original