The need to represent instances of money frequently arises in software development, particularly any financial/economics software. To address that need, the py-moneyed package provides the classes of Money and Currency, at a level more useful than just using Python's Decimal class, or ($DEITY forbid) the float primitive. The package is meant to be stand-alone and easy to either use directly, or subclass further. py-moneyed is BSD-licensed.
Some of the py-moneyed code was first derived from python-money available via this URL: http://code.google.com/p/python-money/ Because that Google Code version has been inactive since May 2008, I forked it and modified it for my needs in 2010. Compared to python-money, major changes here in py-moneyed include separating it from Django usage, tightening types handling in operators, a complete suite of unit tests, PEP8 adherence, providing a setup.py, and local currency formatting/display.
On to the code! The Money class is instantiated with:
- An amount which can be of type int, string, float, or Decimal. It will be converted to a Decimal internally. Therefore, it is best to avoid float objects, since they do not convert losslessly to Decimal.
- A currency, which usually is specified by the three-capital-letters ISO currency code, e.g. USD, EUR, CNY, and so on. It will be converted to a Currency object.
from moneyed import Money sale_price_today = Money(amount='99.99', currency='USD')
You then use Money instances as a normal number. The Money class provides operators with type checking, matching currency checking, and sensible dimensional behavior, e.g. you cannot multiply two Money instances, nor can you add a Money instance to a non-Money number; dividing a Money instance by another results in a Decimal value, etc.
The Currency class is provided with a complete dictionary of ISO 4217 currencies data, each key (e.g. 'USD') mapping to a Currency instance with ISO numeric code, canonical name in English, and countries using the currency. Thanks to the python-money developers for their (possibly tedious) data-entry of the ISO codes!
All of these are available as pre-built Currency objects in the moneyed module.
You can also pass in the arguments to Money as positional arguments. So you can also write:
>>> from moneyed import Money, USD >>> price = Money('19.50', USD) >>> price 19 USD >>> price.amount Decimal('19.50') >>> price.currency USD >>> price.currency.code 'USD'
You can print Money object as follows:
>>> from moneyed.localization import format_money >>> format_money(Money(10, USD), locale='en_US') '$10.00'
Unit-tests have been provided, and can be run with tox (recommended) or just py.test.
If you don't have tox installed on your system, it's a modern Python tool to automate running tests and deployment; install it to your global Python environment with:
sudo pip install tox
Then you can activate a virtualenv (any will do - by design tox will not run from your globally-installed python), cd to the py-moneyed source directory then run the tests at the shell:
cd where/py-moneyed-source/is tox
The py-moneyed package has been tested with Python 2.6, 2.7, 3.2, 3.3 and PyPy 2.1.
Future versions of py-moneyed may provide currency conversions or other capabilities, dependent on feedback and usage.