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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 _Aff4Size(aff4_obj):
 """Retrieves the total size in bytes of an AFF4 object. Args: aff4_obj: An AFF4 stream instance to retrieve size for. Returns: An integer representing number of bytes. Raises: TypeError: If `aff4_obj` is not an instance of AFF4 stream. """

  if not isinstance(aff4_obj, aff4.AFF4Stream):
    message = "Expected an instance of `%s` but received `%s`"
    raise TypeError(message % (aff4.AFF4Stream, type(aff4_obj)))

  return int(aff4_obj.Get(aff4_obj.Schema.SIZE))