code = amount.currency

        try:

            current_number = currency_map[code].number

        except KeyError:

            current_number = Decimal(0)

        currency_map[code] = data.Amount(current_number + amount.number, code)

    def _add_other(self,

                   currency_map: MutableMapping[str, data.Amount],

                   other: Union[data.Amount, 'Balance'],

    ) -> None:

        if isinstance(other, Balance):

            for amount in other.values():

                self._add_amount(currency_map, amount)

        else:

            self._add_amount(currency_map, other)

    def __repr__(self) -> str:

        values = [repr(amt) for amt in self.values()]

        return f"{type(self).__name__}({values!r})"

    def __str__(self) -> str:

        return self.format()

    def __abs__(self: BalanceType) -> BalanceType:

        return type(self)(bc_amount.abs(amt) for amt in self.values())

    def __add__(self: BalanceType, other: Union[data.Amount, 'Balance']) -> BalanceType:

        retval_map = self._currency_map.copy()

        self._add_other(retval_map, other)

        return type(self)(retval_map.values())

    def __eq__(self, other: Any) -> bool:

        if isinstance(other, Balance):

            clean_self = self.clean_copy()

            clean_other = other.clean_copy()

            return len(clean_self) == len(clean_other) and all(

                clean_self[key] == clean_other.get(key) for key in clean_self

            )

        else:

            return super().__eq__(other)

    def __neg__(self: BalanceType) -> BalanceType:

        return type(self)(-amt for amt in self.values())

    def __pos__(self: BalanceType) -> BalanceType:

        return self

    def __getitem__(self, key: str) -> data.Amount:

        return self._currency_map[key]

    def __iter__(self) -> Iterator[str]:

        return iter(self._currency_map)

    def __len__(self) -> int:

        return len(self._currency_map)

    def _all_amounts(self,

                     op_func: Callable[[DecimalCompat, DecimalCompat], bool],

                     operand: DecimalCompat,

    ) -> bool:

        return all(op_func(amt.number, operand) for amt in self.values())

    def copy(self: BalanceType) -> BalanceType:

    def format(self,

               fmt: Optional[str]='#,#00.00 ¤¤',

               sep: str=', ',

               empty: str="Zero balance",

               tolerance: Optional[Decimal]=None,

    ) -> str:

        """Formats the balance as a string with the given parameters

        If the balance is zero (within tolerance), returns ``empty``.

        Otherwise, returns a string with each amount in the balance formatted

        as ``fmt``, separated by ``sep``.

        If you set ``fmt`` to None, amounts will be formatted according to the

        user's locale. The default format is Beancount's input format.

        """

        amounts = list(self.clean_copy(tolerance).values())

        if not amounts:

            return empty

        amounts.sort(key=lambda amt: abs(amt.number), reverse=True)

        return sep.join(

            babel.numbers.format_currency(amt.number, amt.currency, fmt)

            for amt in amounts

        )

class MutableBalance(Balance):

    __slots__ = ()

    def __iadd__(self: BalanceType, other: Union[data.Amount, Balance]) -> BalanceType:

        self._add_other(self._currency_map, other)

        return self

class RelatedPostings(Sequence[data.Posting]):

    """Collect and query related postings

    This class provides common functionality for collecting related postings

    and running queries on them: iterating over them, tallying their balance,

    etc.

    This class doesn't know anything about how the postings are related. That's

    entirely up to the caller.

    A common pattern is to use this class with collections.defaultdict

    to organize postings based on some key. See the group_by_meta classmethod

    for an example.

    """

    __slots__ = ('_postings',)

    def __init__(self,

                 source: Iterable[data.Posting]=(),

                 *,

                 _can_own: bool=False,

    ) -> None:

        self._postings: List[data.Posting]

        if _can_own and isinstance(source, list):

            self._postings = source

        else:

            self._postings = list(source)

    @classmethod

    def _group_by(cls: Type[RelatedType],

                  postings: Iterable[data.Posting],

                  key: Callable[[data.Posting], T],

def test_add_amount(number, currency):

    start_amount = testutil.Amount(500, 'USD')

    start_bal = core.Balance([start_amount])

    add_amount = testutil.Amount(number, currency)

    actual = start_bal + add_amount

    if currency == 'USD':

        assert len(actual) == 1

        assert actual['USD'] == testutil.Amount(500 + number)

    else:

        assert len(actual) == 2

        assert actual['USD'] == start_amount

        assert actual[currency] == add_amount

    assert start_bal == {'USD': start_amount}

@pytest.mark.parametrize('number,currency', {

    (50, 'USD'),

    (-50, 'USD'),

    (50000, 'BRL'),

    (-4000, 'BRL'),

})

def test_iadd_amount(number, currency):

    balance = core.MutableBalance([testutil.Amount(500, 'USD')])

    add_amount = testutil.Amount(number, currency)

    balance += add_amount

    if currency == 'USD':

        assert len(balance) == 1

        assert balance['USD'] == testutil.Amount(500 + number)

    else:

        assert len(balance) == 2

        assert balance['USD'] == testutil.Amount(500)

        assert balance[currency] == add_amount

@pytest.mark.parametrize('mapping', [

    {},

    {'USD': 0},

    {'EUR': 10},

    {'JPY': 20, 'BRL': 30},

    {'EUR': -15},

    {'JPY': -25, 'BRL': -35},

    {'JPY': 40, 'USD': 0, 'EUR': -50},

])

def test_add_balance(mapping):

    expect_numbers = {'USD': 500, 'BRL': 40000}

    start_bal = core.Balance(amounts_from_map(expect_numbers))

    for code, number in mapping.items():

        expect_numbers[code] = expect_numbers.get(code, 0) + number

    add_bal = core.Balance(amounts_from_map(mapping))

    actual = start_bal + add_bal

    expected = core.Balance(amounts_from_map(expect_numbers))

    assert actual == expected

@pytest.mark.parametrize('mapping', [

    {},

    {'USD': 0},

    {'EUR': 10},

    {'JPY': 20, 'BRL': 30},

    {'EUR': -15},

    {'JPY': -25, 'BRL': -35},

    {'JPY': 40, 'USD': 0, 'EUR': -50},

])

def test_iadd_balance(mapping):

    expect_numbers = {'USD': 500, 'BRL': 40000}

    balance = core.MutableBalance(amounts_from_map(expect_numbers))

    for code, number in mapping.items():