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https://github.com/carlospalol/money

Python money class with optional CLDR-backed locale-aware formatting and an extensible currency exchange solution.
https://github.com/carlospalol/money

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Python money class with optional CLDR-backed locale-aware formatting and an extensible currency exchange solution.

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README 

        

============

Python Money

============



Money class with optional CLDR-backed locale-aware formatting and an extensible currency exchange solution.



.. RADAR: version



**This is version 1.4.0-dev**.



:Development: https://github.com/carlospalol/money

:Latest release: https://pypi.python.org/pypi/money/



This package is compatible with Python 2.7, 3.4, 3.5, but there are important `Differences between Python versions`_. All code examples use Python 3.5.



**Contents**



.. contents::

    :local:

    :backlinks: none



Installation

============



Install the latest release with:



::



    pip install money



For locale-aware formatting, also install the latest version of `Babel `_ (2.2 or 2.3 required):



::



    pip install babel



Usage

=====



.. code:: python



    >>> from money import Money

    >>> m = Money(amount='2.22', currency='EUR')

    >>> m

    EUR 2.22



*amount* can be any valid value in ``decimal.Decimal(value)`` and *currency* should be a three-letter currency code. Money objects are immutable by convention and hashable. Once created, you can use read-only properties ``amount`` (decimal.Decimal) and ``currency`` (str) to access its internal components:



.. code:: python



    >>> m = Money(2, 'USD')

    >>> m.amount

    Decimal('2')

    >>> m.currency

    'USD'



Money emulates a numeric type and you can apply most arithmetic and comparison operators between money objects, as well as addition, subtraction, and division with integers (int) and decimal numbers (decimal.Decimal):



.. code:: python



    >>> m = Money('2.22', 'EUR')

    >>> m / 2

    EUR 1.11

    >>> m + Money('7.77', 'EUR')

    EUR 9.99



More formally, with *AAA* and *BBB* being different currencies:



+-----------+---------------+-----------+-----------+-----------------+

|           | Operator      | Money AAA | Money BBB | int, Decimal    |

+===========+===============+===========+===========+=================+

| **Money   | ``+``, ``-``  | Money     | N/A       | Money           |

+ AAA**     +---------------+-----------+-----------+-----------------+

|           | ``*``         | N/A       | N/A       | Money           |

+           +---------------+-----------+-----------+-----------------+

|           | ``/``, ``//`` | Decimal   | N/A       | Money           |

+           +---------------+-----------+-----------+-----------------+

|           | ``>``, ``>=`` | Compares  | N/A       | N/A             |

|           | ``<``, ``<=`` | amount.   |           |                 |

+           +---------------+           +-----------+-----------------+

|           | ``==``        |           | False     | False           |

|           |               |           |           |                 |

+-----------+---------------+-----------+-----------+-----------------+



Arithmetic operations with floats are not directly supported. If you need to operate with floats, you must first convert the float to a Decimal, or the Money object to a float (i.e. float(m)). Please be aware of the `issues and limitations of floating point arithmetics `_.



Currency presets

----------------



If you use fixed currencies in your code, you may find convenient to create currency-preset Money subclasses:



.. code:: python



    class EUR(Money):

        def __init__(self, amount='0'):

            super().__init__(amount=amount, currency='EUR')

    

    price = EUR('9.99')



Formatting

==========



Money objects are printed by default with en_US formatting and the currency code.



.. code:: python



    >>> m = Money('1234.567', 'EUR')

    >>> str(m)

    'EUR 1,234.57'



Use ``format(locale=LC_NUMERIC, pattern=None, currency_digits=True, format_type='standard')`` for locale-aware formatting with currency expansion. ``format()`` relies on ``babel.numbers.format_currency()``, and **requires Babel** to be installed.



.. code:: python



    >>> m = Money('1234.567', 'USD')

    >>> m.format('en_US')

    '$1,234.57'

    >>> m.format('es_ES')

    '1.234,57\xa0$'



The character ``\xa0`` is an unicode non-breaking space. If no locale is passed, Babel will use your system's locale. You can also provide a specific pattern to format():



.. code:: python



    >>> m = Money('-1234.567', 'USD')

    >>> # Regular US format:

    >>> m.format('en_US', '¤#,##0.00') 

    '-$1,234.57'

    >>> # Custom negative format:

    >>> m.format('en_US', '¤#,##0.00;<¤#,##0.00>')

    '<$1,234.57>'

    >>> # Spanish format, full currency name:

    >>> m.format('es_ES', '#,##0.00 ¤¤¤')

    '-1.234,57 dólares estadounidenses'

    >>> # Same as above, but rounding (overriding currency natural format):

    >>> m.format('es_ES', '#0 ¤¤¤', currency_digits=False)

    '-1235 dólares estadounidenses'



For more details on formatting see `Babel docs on currency formatting `_. To learn more about the formatting pattern syntax check out `Unicode TR35 `_.



Currency exchange

=================



Currency exchange works by "installing" a **backend** class that implements the abstract base class (`abc `_) ``money.exchange.BackendBase``. Its API is exposed through ``money.xrates``, along with setup functions ``xrates.install(pythonpath)``, ``xrates.uninstall()``, and ``xrates.backend_name``.



A simple proof-of-concept backend ``money.exchange.SimpleBackend`` is included:



.. code:: python



    from decimal import Decimal

    from money import Money, xrates



    xrates.install('money.exchange.SimpleBackend')

    xrates.base = 'USD'

    xrates.setrate('AAA', Decimal('2'))

    xrates.setrate('BBB', Decimal('8'))

    

    a = Money(1, 'AAA')

    b = Money(1, 'BBB')

    

    assert a.to('BBB') == Money('4', 'BBB')

    assert b.to('AAA') == Money('0.25', 'AAA')

    assert a + b.to('AAA') == Money('1.25', 'AAA')



XMoney

======



You can use ``money.XMoney`` (a subclass of Money), for automatic currency conversion while adding, subtracting, and dividing money objects (+, +=, -, -=, /, //). This is useful when aggregating lots of money objects with heterogeneous currencies. The currency of the leftmost object has priority.



.. code:: python



    from money import XMoney

    

    # Register backend and rates as above...

    

    a = XMoney(1, 'AAA')

    b = XMoney(1, 'BBB')

    

    assert sum([a, b]) == XMoney('1.25', 'AAA')



Exceptions

==========



Found in ``money.exceptions``.



``MoneyException(Exception)``

    Base class for all exceptions.



``CurrencyMismatch(MoneyException, ValueError)``

    Thrown when mixing different currencies, e.g. ``Money(2, 'EUR') + Money(2, 'USD')``. Money objects must be converted first to the same currency, or XMoney could be used for automatic conversion.



``InvalidOperandType(MoneyException, TypeError)``

    Thrown when attempting invalid operations, e.g. multiplication between money objects.



``ExchangeError(MoneyException)``

    Base class for exchange exceptions.



``ExchangeBackendNotInstalled(ExchangeError)``

    Thrown if a conversion is attempted, but there is no backend available.



``ExchangeRateNotFound(ExchangeError)``

    The installed backend failed to provide a suitable exchange rate between the origin and target currencies.



Hierarchy

---------



* ``MoneyException``

    * ``CurrencyMismatch``

    * ``InvalidOperandType``

    * ``ExchangeError``

        * ``ExchangeBackendNotInstalled``

        * ``ExchangeRateNotFound``



.. _python-differences:



Differences between Python versions

===================================



.. list-table::

    :header-rows: 1

    :stub-columns: 1

    

    * - Expression

      - Python 2.x

      - Python 3.x

    

    * - ``round(Money('2.5', 'EUR'))``

      - Returns ``3.0``, a **float** rounded amount **away from zero**.

      - Returns ``EUR 2``, a **Money object** with rounded amount to the **nearest even**.

    

    * - ``Money('0', 'EUR').amount < '0'``

      - Returns ``True``. This is the weird but expected behaviour in Python 2.x when comparing Decimal objects with non-numerical objects (Note the '0' is a string). `See note in docs `_.

      - TypeError: unorderable types: decimal.Decimal() > str()



Design decisions

================



There are several design decisions in *money* that differ from currently available money class implementations:



Localization

------------



Do not keep any kind of locale conventions database inside this package. Locale conventions are extensive and change over time; keeping track of them is a project of its own. There is already such a project and database (the Unicode Common Locale Data Repository), and an excellent python API for it: `Babel `_.



Currency

--------



There is no need for a currency class. A currency is fully identified by its ISO 4217 code, and localization or exchange rates data are expected to be centralized as databases/services because of their changing nature.



Also:



+ **Modulo operator (%)**: do not override to mean "percentage".

+ **Numeric type**: you **can** mix numbers and money in binary operations, and objects evaluate to False if their amount is zero.

+ **Global default currency**: subclassing is a safer solution.



Contributions

=============



Contributions are welcome. You can use the `regular github mechanisms `_.



To test your changes you will need `tox `_ and python 2.7, 3.4, and 3.5. Simply cd to the package root (by setup.py) and run ``tox``.



License

=======



money is released under the **MIT license**, which can be found in the file ``LICENSE``.