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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 validate(cls, mapper_spec):
 """Validates mapper spec. Args: mapper_spec: The MapperSpec for this InputReader. Raises: BadReaderParamsError: required parameters are missing or invalid. """

    if mapper_spec.input_reader_class() != cls:
      raise BadReaderParamsError("Input reader class mismatch")
    params = _get_params(mapper_spec)
    if cls.BATCH_SIZE_PARAM in params:
      try:
        batch_size = int(params[cls.BATCH_SIZE_PARAM])
        if batch_size < 1:
          raise BadReaderParamsError("Bad batch size: %s" % batch_size)
      except ValueError, e:
        raise BadReaderParamsError("Bad batch size: %s" % e)