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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 _ExpandArtifactGroupSource(self, source, requested):
 """Recursively expands an artifact group source."""

    artifact_list = []
    if "names" in source.attributes:
      artifact_list = source.attributes["names"]
    for artifact_name in artifact_list:
      if artifact_name in self.processed_artifacts:
        continue
      artifact_obj = artifact_registry.REGISTRY.GetArtifact(artifact_name)
      for expanded_artifact in self.Expand(artifact_obj, requested):
        yield expanded_artifact