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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 create_indexed_document(index_instance, model_items, action):
    '''
    Creates the document that will be passed into the bulk index function.
    Either a list of serialized objects to index, or a a dictionary specifying the primary keys of items to be delete.
    '''
    data = []
    if action == 'delete':
        for pk in model_items:
            data.append({'_id': pk, '_op_type': action})
    else:
        for doc in model_items:
            if index_instance.matches_indexing_condition(doc):
                data.append(index_instance.serialize_object(doc))
    return data