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.
For example,
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'This package uses the special method __truediv__ to add division support to Money class. So, if you are using python 2, make sure that you have imported division on your code that calls division operation, otherwise you will get unsupported operand error.
>>> from __future__ import division
>>> from moneyed import Money
>>> price = Money(amount='50', currency='USD')
>>> price / 2
<Money: 25 USD>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
If you do not have all versions of Python that are used in testing, you can use pyenv. After installing pyenv, install the additional plugin pyenv-implict.
The py-moneyed package is tested against Python 2.6, 2.7, 3.2, 3.3, 3.4, 3.5, and PyPy 2.1.
Future versions of py-moneyed may provide currency conversions or other capabilities, dependent on feedback and usage.