# Extending a Schema

With GraphQL-core 3 you can also extend a given schema using type extensions. For example, we might want to add a `lastName` property to our `Human` data type to retrieve only the last name of the person.

This can be achieved with the `extend_schema()` function as follows:

    from graphql import extend_schema, parse

    schema = extend_schema(schema, parse("""
        extend type Human {
         lastName: String
        }
        """))

Note that this function expects the extensions as an AST, which we can get using the `parse()` function. Also note that the `extend_schema()` function does not alter the original schema, but returns a new schema object.

We also need to attach a resolver function to the new field:

    def get_last_name(human, info):
        return human['name'].rsplit(None, 1)[-1]

    schema.get_type('Human').fields['lastName'].resolve = get_last_name

Now we can query only the last name of a human:

    from graphql import graphql_sync

    result = graphql_sync(schema, """
        {
          human(id: "1000") {
            lastName
            homePlanet
          }
        }
        """)
    print(result)

This query will give the following result:

    ExecutionResult(
        data={'human': {'lastName': 'Skywalker', 'homePlanet': 'Tatooine'}},
        errors=None)