Retrieve artifact classes with optional filtering.

    All filters must match for the artifact to be returned.

    Args:
      os_name: string to match against supported_os
      name_list: list of strings to match against artifact names
      source_type: rdf_artifacts.ArtifactSource.SourceType to match against
        source_type
      exclude_dependents: if true only artifacts with no dependencies will be
        returned
      provides: return the artifacts that provide these dependencies
      reload_datastore_artifacts: If true, the data store sources are queried
        for new artifacts.

    Returns:
      set of artifacts matching filter criteria

def GetArtifacts(self,
                   os_name=None,
                   name_list=None,
                   source_type=None,
                   exclude_dependents=False,
                   provides=None,
                   reload_datastore_artifacts=False):
    """Retrieve artifact classes with optional filtering.

    All filters must match for the artifact to be returned.

    Args:
      os_name: string to match against supported_os
      name_list: list of strings to match against artifact names
      source_type: rdf_artifacts.ArtifactSource.SourceType to match against
        source_type
      exclude_dependents: if true only artifacts with no dependencies will be
        returned
      provides: return the artifacts that provide these dependencies
      reload_datastore_artifacts: If true, the data store sources are queried
        for new artifacts.

    Returns:
      set of artifacts matching filter criteria
    """
    self._CheckDirty(reload_datastore_artifacts=reload_datastore_artifacts)
    results = set()
    for artifact in itervalues(self._artifacts):

      # artifact.supported_os = [] matches all OSes
      if os_name and artifact.supported_os and (
          os_name not in artifact.supported_os):
        continue
      if name_list and artifact.name not in name_list:
        continue
      if source_type:
        source_types = [c.type for c in artifact.sources]
        if source_type not in source_types:
          continue
      if exclude_dependents and GetArtifactPathDependencies(artifact):
        continue

      if not provides:
        results.add(artifact)
      else:
        # This needs to remain the last test, if it matches the result is added
        for provide_string in artifact.provides:
          if provide_string in provides:
            results.add(artifact)
            break

    return results