sqlalchemy/test/ext/test_hybrid.py

from sqlalchemy import func, Integer, Numeric, String, ForeignKey
from sqlalchemy.orm import relationship, Session, aliased, persistence
from sqlalchemy.testing.schema import Column
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext import hybrid
from sqlalchemy.testing import eq_, is_, AssertsCompiledSQL, \
    assert_raises_message
from sqlalchemy.testing import fixtures
from sqlalchemy import inspect
from decimal import Decimal


class PropertyComparatorTest(fixtures.TestBase, AssertsCompiledSQL):
    __dialect__ = 'default'

    def _fixture(self):
        Base = declarative_base()

        class UCComparator(hybrid.Comparator):

            def __eq__(self, other):
                if other is None:
                    return self.expression is None
                else:
                    return func.upper(self.expression) == func.upper(other)

        class A(Base):
            __tablename__ = 'a'
            id = Column(Integer, primary_key=True)

            _value = Column("value", String)

            @hybrid.hybrid_property
            def value(self):
                "This is a docstring"
                return self._value - 5

            @value.comparator
            def value(cls):
                return UCComparator(cls._value)

            @value.setter
            def value(self, v):
                self._value = v + 5

        return A

    def test_set_get(self):
        A = self._fixture()
        a1 = A(value=5)
        eq_(a1._value, 10)
        eq_(a1.value, 5)

    def test_value(self):
        A = self._fixture()
        eq_(str(A.value == 5), "upper(a.value) = upper(:upper_1)")

    def test_aliased_value(self):
        A = self._fixture()
        eq_(str(aliased(A).value == 5), "upper(a_1.value) = upper(:upper_1)")

    def test_query(self):
        A = self._fixture()
        sess = Session()
        self.assert_compile(
            sess.query(A.value),
            "SELECT a.value AS a_value FROM a"
        )

    def test_aliased_query(self):
        A = self._fixture()
        sess = Session()
        self.assert_compile(
            sess.query(aliased(A).value),
            "SELECT a_1.value AS a_1_value FROM a AS a_1"
        )

    def test_aliased_filter(self):
        A = self._fixture()
        sess = Session()
        self.assert_compile(
            sess.query(aliased(A)).filter_by(value="foo"),
            "SELECT a_1.value AS a_1_value, a_1.id AS a_1_id "
            "FROM a AS a_1 WHERE upper(a_1.value) = upper(:upper_1)"
        )

    def test_docstring(self):
        A = self._fixture()
        eq_(A.value.__doc__, "This is a docstring")


class PropertyExpressionTest(fixtures.TestBase, AssertsCompiledSQL):
    __dialect__ = 'default'

    def _fixture(self):
        Base = declarative_base()

        class A(Base):
            __tablename__ = 'a'
            id = Column(Integer, primary_key=True)
            _value = Column("value", String)

            @hybrid.hybrid_property
            def value(self):
                "This is an instance-level docstring"
                return int(self._value) - 5

            @value.expression
            def value(cls):
                "This is a class-level docstring"
                return func.foo(cls._value) + cls.bar_value

            @value.setter
            def value(self, v):
                self._value = v + 5

            @hybrid.hybrid_property
            def bar_value(cls):
                return func.bar(cls._value)

        return A


    def _relationship_fixture(self):
        Base = declarative_base()

        class A(Base):
            __tablename__ = 'a'
            id = Column(Integer, primary_key=True)
            b_id = Column('bid', Integer, ForeignKey('b.id'))
            _value = Column("value", String)

            @hybrid.hybrid_property
            def value(self):
                return int(self._value) - 5

            @value.expression
            def value(cls):
                return func.foo(cls._value) + cls.bar_value

            @value.setter
            def value(self, v):
                self._value = v + 5

            @hybrid.hybrid_property
            def bar_value(cls):
                return func.bar(cls._value)

        class B(Base):
            __tablename__ = 'b'
            id = Column(Integer, primary_key=True)

            as_ = relationship("A")

        return A, B

    def test_info(self):
        A = self._fixture()
        inspect(A).all_orm_descriptors.value.info["some key"] = "some value"
        eq_(
            inspect(A).all_orm_descriptors.value.info,
            {"some key": "some value"}
        )

    def test_set_get(self):
        A = self._fixture()
        a1 = A(value=5)
        eq_(a1._value, 10)
        eq_(a1.value, 5)

    def test_expression(self):
        A = self._fixture()
        self.assert_compile(
            A.value.__clause_element__(),
            "foo(a.value) + bar(a.value)"
        )

    def test_any(self):
        A, B = self._relationship_fixture()
        sess = Session()
        self.assert_compile(
            sess.query(B).filter(B.as_.any(value=5)),
            "SELECT b.id AS b_id FROM b WHERE EXISTS "
            "(SELECT 1 FROM a WHERE b.id = a.bid "
            "AND foo(a.value) + bar(a.value) = :param_1)"
        )

    def test_aliased_expression(self):
        A = self._fixture()
        self.assert_compile(
            aliased(A).value.__clause_element__(),
            "foo(a_1.value) + bar(a_1.value)"
        )

    def test_query(self):
        A = self._fixture()
        sess = Session()
        self.assert_compile(
            sess.query(A).filter_by(value="foo"),
            "SELECT a.value AS a_value, a.id AS a_id "
            "FROM a WHERE foo(a.value) + bar(a.value) = :param_1"
        )

    def test_aliased_query(self):
        A = self._fixture()
        sess = Session()
        self.assert_compile(
            sess.query(aliased(A)).filter_by(value="foo"),
            "SELECT a_1.value AS a_1_value, a_1.id AS a_1_id "
            "FROM a AS a_1 WHERE foo(a_1.value) + bar(a_1.value) = :param_1"
        )

    def test_docstring(self):
        A = self._fixture()
        eq_(A.value.__doc__, "This is a class-level docstring")

        # no docstring here since we get a literal
        a1 = A(_value=10)
        eq_(a1.value, 5)


class PropertyValueTest(fixtures.TestBase, AssertsCompiledSQL):
    __dialect__ = 'default'

    def _fixture(self, assignable):
        Base = declarative_base()

        class A(Base):
            __tablename__ = 'a'
            id = Column(Integer, primary_key=True)
            _value = Column("value", String)

            @hybrid.hybrid_property
            def value(self):
                return self._value - 5

            if assignable:
                @value.setter
                def value(self, v):
                    self._value = v + 5

        return A

    def test_nonassignable(self):
        A = self._fixture(False)
        a1 = A(_value=5)
        assert_raises_message(
            AttributeError,
            "can't set attribute",
            setattr, a1, 'value', 10
        )

    def test_nondeletable(self):
        A = self._fixture(False)
        a1 = A(_value=5)
        assert_raises_message(
            AttributeError,
            "can't delete attribute",
            delattr, a1, 'value'
        )

    def test_set_get(self):
        A = self._fixture(True)
        a1 = A(value=5)
        eq_(a1.value, 5)
        eq_(a1._value, 10)


class PropertyOverrideTest(fixtures.TestBase, AssertsCompiledSQL):
    __dialect__ = 'default'

    def _fixture(self):
        Base = declarative_base()

        class Person(Base):
            __tablename__ = 'person'
            id = Column(Integer, primary_key=True)
            _name = Column(String)

            @hybrid.hybrid_property
            def name(self):
                return self._name

            @name.setter
            def name(self, value):
                self._name = value.title()

        class OverrideSetter(Person):
            __tablename__ = 'override_setter'
            id = Column(Integer, ForeignKey('person.id'), primary_key=True)
            other = Column(String)

            @Person.name.setter
            def name(self, value):
                self._name = value.upper()

        class OverrideGetter(Person):
            __tablename__ = 'override_getter'
            id = Column(Integer, ForeignKey('person.id'), primary_key=True)
            other = Column(String)

            @Person.name.getter
            def name(self):
                return "Hello " + self._name

        class OverrideExpr(Person):
            __tablename__ = 'override_expr'
            id = Column(Integer, ForeignKey('person.id'), primary_key=True)
            other = Column(String)

            @Person.name.overrides.expression
            def name(self):
                return func.concat("Hello", self._name)

        class FooComparator(hybrid.Comparator):
            def __clause_element__(self):
                return func.concat("Hello", self.expression._name)

        class OverrideComparator(Person):
            __tablename__ = 'override_comp'
            id = Column(Integer, ForeignKey('person.id'), primary_key=True)
            other = Column(String)

            @Person.name.overrides.comparator
            def name(self):
                return FooComparator(self)

        return (
            Person, OverrideSetter, OverrideGetter,
            OverrideExpr, OverrideComparator
        )

    def test_property(self):
        Person, _, _, _, _ = self._fixture()
        p1 = Person()
        p1.name = 'mike'
        eq_(p1._name, 'Mike')
        eq_(p1.name, 'Mike')

    def test_override_setter(self):
        _, OverrideSetter, _, _, _ = self._fixture()
        p1 = OverrideSetter()
        p1.name = 'mike'
        eq_(p1._name, 'MIKE')
        eq_(p1.name, 'MIKE')

    def test_override_getter(self):
        _, _, OverrideGetter, _, _ = self._fixture()
        p1 = OverrideGetter()
        p1.name = 'mike'
        eq_(p1._name, 'Mike')
        eq_(p1.name, 'Hello Mike')

    def test_override_expr(self):
        Person, _, _, OverrideExpr, _ = self._fixture()

        self.assert_compile(
            Person.name.__clause_element__(),
            "person._name"
        )

        self.assert_compile(
            OverrideExpr.name.__clause_element__(),
            "concat(:concat_1, person._name)"
        )

    def test_override_comparator(self):
        Person, _, _, _, OverrideComparator = self._fixture()

        self.assert_compile(
            Person.name.__clause_element__(),
            "person._name"
        )

        self.assert_compile(
            OverrideComparator.name.__clause_element__(),
            "concat(:concat_1, person._name)"
        )


class PropertyMirrorTest(fixtures.TestBase, AssertsCompiledSQL):
    __dialect__ = 'default'

    def _fixture(self):
        Base = declarative_base()

        class A(Base):
            __tablename__ = 'a'
            id = Column(Integer, primary_key=True)
            _value = Column("value", String)

            @hybrid.hybrid_property
            def value(self):
                "This is an instance-level docstring"
                return self._value
        return A

    def test_property(self):
        A = self._fixture()

        is_(A.value.property, A._value.property)

    def test_key(self):
        A = self._fixture()
        eq_(A.value.key, "value")
        eq_(A._value.key, "_value")

    def test_class(self):
        A = self._fixture()
        is_(A.value.class_, A._value.class_)

    def test_get_history(self):
        A = self._fixture()
        inst = A(_value=5)
        eq_(A.value.get_history(inst), A._value.get_history(inst))

    def test_info_not_mirrored(self):
        A = self._fixture()
        A._value.info['foo'] = 'bar'
        A.value.info['bar'] = 'hoho'

        eq_(A._value.info, {'foo': 'bar'})
        eq_(A.value.info, {'bar': 'hoho'})

    def test_info_from_hybrid(self):
        A = self._fixture()
        A._value.info['foo'] = 'bar'
        A.value.info['bar'] = 'hoho'

        insp = inspect(A)
        is_(insp.all_orm_descriptors['value'].info, A.value.info)


class MethodExpressionTest(fixtures.TestBase, AssertsCompiledSQL):
    __dialect__ = 'default'

    def _fixture(self):
        Base = declarative_base()

        class A(Base):
            __tablename__ = 'a'
            id = Column(Integer, primary_key=True)
            _value = Column("value", String)

            @hybrid.hybrid_method
            def value(self, x):
                "This is an instance-level docstring"
                return int(self._value) + x

            @value.expression
            def value(cls, value):
                "This is a class-level docstring"
                return func.foo(cls._value, value) + value

            @hybrid.hybrid_method
            def other_value(self, x):
                "This is an instance-level docstring"
                return int(self._value) + x

            @other_value.expression
            def other_value(cls, value):
                return func.foo(cls._value, value) + value

        return A

    def test_call(self):
        A = self._fixture()
        a1 = A(_value=10)
        eq_(a1.value(7), 17)

    def test_expression(self):
        A = self._fixture()
        self.assert_compile(
            A.value(5),
            "foo(a.value, :foo_1) + :foo_2"
        )

    def test_info(self):
        A = self._fixture()
        inspect(A).all_orm_descriptors.value.info["some key"] = "some value"
        eq_(
            inspect(A).all_orm_descriptors.value.info,
            {"some key": "some value"}
        )

    def test_aliased_expression(self):
        A = self._fixture()
        self.assert_compile(
            aliased(A).value(5),
            "foo(a_1.value, :foo_1) + :foo_2"
        )

    def test_query(self):
        A = self._fixture()
        sess = Session()
        self.assert_compile(
            sess.query(A).filter(A.value(5) == "foo"),
            "SELECT a.value AS a_value, a.id AS a_id "
            "FROM a WHERE foo(a.value, :foo_1) + :foo_2 = :param_1"
        )

    def test_aliased_query(self):
        A = self._fixture()
        sess = Session()
        a1 = aliased(A)
        self.assert_compile(
            sess.query(a1).filter(a1.value(5) == "foo"),
            "SELECT a_1.value AS a_1_value, a_1.id AS a_1_id "
            "FROM a AS a_1 WHERE foo(a_1.value, :foo_1) + :foo_2 = :param_1"
        )

    def test_query_col(self):
        A = self._fixture()
        sess = Session()
        self.assert_compile(
            sess.query(A.value(5)),
            "SELECT foo(a.value, :foo_1) + :foo_2 AS anon_1 FROM a"
        )

    def test_aliased_query_col(self):
        A = self._fixture()
        sess = Session()
        self.assert_compile(
            sess.query(aliased(A).value(5)),
            "SELECT foo(a_1.value, :foo_1) + :foo_2 AS anon_1 FROM a AS a_1"
        )

    def test_docstring(self):
        A = self._fixture()
        eq_(A.value.__doc__, "This is a class-level docstring")
        eq_(A.other_value.__doc__, "This is an instance-level docstring")
        a1 = A(_value=10)

        # a1.value is still a method, so it has a
        # docstring
        eq_(a1.value.__doc__, "This is an instance-level docstring")

        eq_(a1.other_value.__doc__, "This is an instance-level docstring")


class BulkUpdateTest(fixtures.DeclarativeMappedTest, AssertsCompiledSQL):
    __dialect__ = 'default'

    @classmethod
    def setup_classes(cls):
        Base = cls.DeclarativeBasic

        class Person(Base):
            __tablename__ = 'person'

            id = Column(Integer, primary_key=True)
            first_name = Column(String(10))
            last_name = Column(String(10))

            @hybrid.hybrid_property
            def name(self):
                return self.first_name + ' ' + self.last_name

            @name.setter
            def name(self, value):
                self.first_name, self.last_name = value.split(' ', 1)

            @name.expression
            def name(cls):
                return func.concat(cls.first_name, ' ', cls.last_name)

            @name.update_expression
            def name(cls, value):
                f, l = value.split(' ', 1)
                return [(cls.first_name, f), (cls.last_name, l)]

            @hybrid.hybrid_property
            def uname(self):
                return self.name

            @hybrid.hybrid_property
            def fname(self):
                return self.first_name

            @hybrid.hybrid_property
            def fname2(self):
                return self.fname

    @classmethod
    def insert_data(cls):
        s = Session()
        jill = cls.classes.Person(id=3, first_name='jill')
        s.add(jill)
        s.commit()

    def test_update_plain(self):
        Person = self.classes.Person

        s = Session()
        q = s.query(Person)

        bulk_ud = persistence.BulkUpdate.factory(
            q, False, {Person.fname: "Dr."}, {})

        self.assert_compile(
            bulk_ud,
            "UPDATE person SET first_name=:first_name",
            params={'first_name': 'Dr.'}
        )

    def test_update_expr(self):
        Person = self.classes.Person

        s = Session()
        q = s.query(Person)

        bulk_ud = persistence.BulkUpdate.factory(
            q, False, {Person.name: "Dr. No"}, {})

        self.assert_compile(
            bulk_ud,
            "UPDATE person SET first_name=:first_name, last_name=:last_name",
            params={'first_name': 'Dr.', 'last_name': 'No'}
        )

    def test_evaluate_hybrid_attr_indirect(self):
        Person = self.classes.Person

        s = Session()
        jill = s.query(Person).get(3)

        s.query(Person).update(
            {Person.fname2: 'moonbeam'},
            synchronize_session='evaluate')
        eq_(jill.fname2, 'moonbeam')

    def test_evaluate_hybrid_attr_plain(self):
        Person = self.classes.Person

        s = Session()
        jill = s.query(Person).get(3)

        s.query(Person).update(
            {Person.fname: 'moonbeam'},
            synchronize_session='evaluate')
        eq_(jill.fname, 'moonbeam')

    def test_fetch_hybrid_attr_indirect(self):
        Person = self.classes.Person

        s = Session()
        jill = s.query(Person).get(3)

        s.query(Person).update(
            {Person.fname2: 'moonbeam'},
            synchronize_session='fetch')
        eq_(jill.fname2, 'moonbeam')

    def test_fetch_hybrid_attr_plain(self):
        Person = self.classes.Person

        s = Session()
        jill = s.query(Person).get(3)

        s.query(Person).update(
            {Person.fname: 'moonbeam'},
            synchronize_session='fetch')
        eq_(jill.fname, 'moonbeam')

    def test_evaluate_hybrid_attr_w_update_expr(self):
        Person = self.classes.Person

        s = Session()
        jill = s.query(Person).get(3)

        s.query(Person).update(
            {Person.name: 'moonbeam sunshine'},
            synchronize_session='evaluate')
        eq_(jill.name, 'moonbeam sunshine')

    def test_fetch_hybrid_attr_w_update_expr(self):
        Person = self.classes.Person

        s = Session()
        jill = s.query(Person).get(3)

        s.query(Person).update(
            {Person.name: 'moonbeam sunshine'},
            synchronize_session='fetch')
        eq_(jill.name, 'moonbeam sunshine')

    def test_evaluate_hybrid_attr_indirect_w_update_expr(self):
        Person = self.classes.Person

        s = Session()
        jill = s.query(Person).get(3)

        s.query(Person).update(
            {Person.uname: 'moonbeam sunshine'},
            synchronize_session='evaluate')
        eq_(jill.uname, 'moonbeam sunshine')


class SpecialObjectTest(fixtures.TestBase, AssertsCompiledSQL):
    """tests against hybrids that return a non-ClauseElement.

    use cases derived from the example at
    http://techspot.zzzeek.org/2011/10/21/hybrids-and-value-agnostic-types/

    """
    __dialect__ = 'default'

    @classmethod
    def setup_class(cls):
        from sqlalchemy import literal

        symbols = ('usd', 'gbp', 'cad', 'eur', 'aud')
        currency_lookup = dict(
            ((currency_from, currency_to), Decimal(str(rate)))
            for currency_to, values in zip(
                symbols,
                [
                    (1, 1.59009, 0.988611, 1.37979, 1.02962),
                    (0.628895, 1, 0.621732, 0.867748, 0.647525),
                    (1.01152, 1.6084, 1, 1.39569, 1.04148),
                    (0.724743, 1.1524, 0.716489, 1, 0.746213),
                    (0.971228, 1.54434, 0.960166, 1.34009, 1),
                ])
            for currency_from, rate in zip(symbols, values)
        )

        class Amount(object):
            def __init__(self, amount, currency):
                self.currency = currency
                self.amount = amount

            def __add__(self, other):
                return Amount(
                    self.amount +
                    other.as_currency(self.currency).amount,
                    self.currency
                )

            def __sub__(self, other):
                return Amount(
                    self.amount -
                    other.as_currency(self.currency).amount,
                    self.currency
                )

            def __lt__(self, other):
                return self.amount < other.as_currency(self.currency).amount

            def __gt__(self, other):
                return self.amount > other.as_currency(self.currency).amount

            def __eq__(self, other):
                return self.amount == other.as_currency(self.currency).amount

            def as_currency(self, other_currency):
                return Amount(
                    currency_lookup[(self.currency, other_currency)] *
                    self.amount,
                    other_currency
                )

            def __clause_element__(self):
                # helper method for SQLAlchemy to interpret
                # the Amount object as a SQL element
                if isinstance(self.amount, (float, int, Decimal)):
                    return literal(self.amount)
                else:
                    return self.amount

            def __str__(self):
                return "%2.4f %s" % (self.amount, self.currency)

            def __repr__(self):
                return "Amount(%r, %r)" % (self.amount, self.currency)

        Base = declarative_base()

        class BankAccount(Base):
            __tablename__ = 'bank_account'
            id = Column(Integer, primary_key=True)

            _balance = Column('balance', Numeric)

            @hybrid.hybrid_property
            def balance(self):
                """Return an Amount view of the current balance."""
                return Amount(self._balance, "usd")

            @balance.setter
            def balance(self, value):
                self._balance = value.as_currency("usd").amount

        cls.Amount = Amount
        cls.BankAccount = BankAccount

    def test_instance_one(self):
        BankAccount, Amount = self.BankAccount, self.Amount
        account = BankAccount(balance=Amount(4000, "usd"))

        # 3b. print balance in usd
        eq_(account.balance.amount, 4000)

    def test_instance_two(self):
        BankAccount, Amount = self.BankAccount, self.Amount
        account = BankAccount(balance=Amount(4000, "usd"))

        # 3c. print balance in gbp
        eq_(account.balance.as_currency("gbp").amount, Decimal('2515.58'))

    def test_instance_three(self):
        BankAccount, Amount = self.BankAccount, self.Amount
        account = BankAccount(balance=Amount(4000, "usd"))

        # 3d. perform currency-agnostic comparisons, math
        is_(account.balance > Amount(500, "cad"), True)

    def test_instance_four(self):
        BankAccount, Amount = self.BankAccount, self.Amount
        account = BankAccount(balance=Amount(4000, "usd"))
        eq_(
            account.balance + Amount(500, "cad") - Amount(50, "eur"),
            Amount(Decimal("4425.316"), "usd")
        )

    def test_query_one(self):
        BankAccount, Amount = self.BankAccount, self.Amount
        session = Session()

        query = session.query(BankAccount).\
            filter(BankAccount.balance == Amount(10000, "cad"))

        self.assert_compile(
            query,
            "SELECT bank_account.balance AS bank_account_balance, "
            "bank_account.id AS bank_account_id FROM bank_account "
            "WHERE bank_account.balance = :balance_1",
            checkparams={'balance_1': Decimal('9886.110000')}
        )

    def test_query_two(self):
        BankAccount, Amount = self.BankAccount, self.Amount
        session = Session()

        # alternatively we can do the calc on the DB side.
        query = session.query(BankAccount).\
            filter(
                BankAccount.balance.as_currency("cad") > Amount(9999, "cad")).\
            filter(
                BankAccount.balance.as_currency("cad") < Amount(10001, "cad"))
        self.assert_compile(
            query,
            "SELECT bank_account.balance AS bank_account_balance, "
            "bank_account.id AS bank_account_id "
            "FROM bank_account "
            "WHERE :balance_1 * bank_account.balance > :param_1 "
            "AND :balance_2 * bank_account.balance < :param_2",
            checkparams={
                'balance_1': Decimal('1.01152'),
                'balance_2': Decimal('1.01152'),
                'param_1': Decimal('9999'),
                'param_2': Decimal('10001')}
        )

    def test_query_three(self):
        BankAccount = self.BankAccount
        session = Session()

        query = session.query(BankAccount).\
            filter(
                BankAccount.balance.as_currency("cad") >
                BankAccount.balance.as_currency("eur"))
        self.assert_compile(
            query,
            "SELECT bank_account.balance AS bank_account_balance, "
            "bank_account.id AS bank_account_id FROM bank_account "
            "WHERE :balance_1 * bank_account.balance > "
            ":param_1 * :balance_2 * bank_account.balance",
            checkparams={
                'balance_1': Decimal('1.01152'),
                'balance_2': Decimal('0.724743'),
                'param_1': Decimal('1.39569')}
        )

    def test_query_four(self):
        BankAccount = self.BankAccount
        session = Session()

        # 4c. query all amounts, converting to "CAD" on the DB side
        query = session.query(BankAccount.balance.as_currency("cad").amount)
        self.assert_compile(
            query,
            "SELECT :balance_1 * bank_account.balance AS anon_1 "
            "FROM bank_account",
            checkparams={'balance_1': Decimal('1.01152')}
        )

    def test_query_five(self):
        BankAccount = self.BankAccount
        session = Session()

        # 4d. average balance in EUR
        query = session.query(func.avg(BankAccount.balance.as_currency("eur")))
        self.assert_compile(
            query,
            "SELECT avg(:balance_1 * bank_account.balance) AS avg_1 "
            "FROM bank_account",
            checkparams={'balance_1': Decimal('0.724743')}
        )

    def test_docstring(self):
        BankAccount = self.BankAccount
        eq_(
            BankAccount.balance.__doc__,
            "Return an Amount view of the current balance.")