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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 setdefault(pb_or_dict, key, value):
 """Set the key on the object to the value if the current value is falsy. Because protobuf Messages do not distinguish between unset values and falsy ones particularly well, this method treats any falsy value (e.g. 0, empty list) as a target to be overwritten, on both Messages and dictionaries. Args: pb_or_dict (Union[~google.protobuf.message.Message, Mapping]):
 the object. key (str):
 The key on the object in question. value (Any):
 The value to set. Raises: TypeError: If pb_or_dict is not a Message or Mapping. """

    if not get(pb_or_dict, key, default=None):
        set(pb_or_dict, key, value)