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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 CreateSourceType(cls, type_indicator, attributes):
 """Creates a source type. Args: type_indicator (str):
 source type indicator. attributes (dict[str, object]):
 source type attributes. Returns: SourceType: a source type. Raises: FormatError: if the type indicator is not set or unsupported, or if required attributes are missing. """

    if type_indicator not in cls._source_type_classes:
      raise errors.FormatError(
          'Unsupported type indicator: {0:s}.'.format(type_indicator))

    return cls._source_type_classes[type_indicator](**attributes)