'Updates the given transformer\'s data dictionary with the given
key and value for the block identified by the given usage_key.
Arguments:
usage_key (UsageKey) - Usage key of the block whose
transformer data is to be updated.
transformer (BlockStructureTransformer) - The transformer
whose data is to be updated.
key (string) - A dictionary key to the transformer\'s data.
value (any picklable type) - The value to associate with the
given key for the given transformer\'s data for the
requested block.'

def set_transformer_block_field(self, usage_key, transformer, key, value):

    setattr(self._get_or_create_block(usage_key).transformer_data.get_or_create(transformer), key, value)
