cached-property 0.1.1

A cached-property for decorating methods in classes.

A cached-property for decorating methods in classes.

• Free software: BSD license
• Documentation: http://cached-property.rtfd.org.

Why?

• Makes caching of time or computational expensive properties quick and easy.
• Because I got tired of copy/pasting this code from non-web project to non-web project.
• I needed something really simple that worked in Python 2 and 3.

How to use it

Define a class with an expensive property. Every time you stay there the price goes up by $50. I

class Monopoly(object):

    def __init__(self):
        self.boardwalk_price = 500

    @property
    def boardwalk(self):
        # In reality, this might represent a database call or time
        # intensive task like calling a third-party API.
        self.boardwalk_price += 50
        return self.boardwalk_price

Now run it:

>>> m = Monopoly()
>>> m.boardwalk
550
>>> m.boardwalk
600

Let’s convert the boardwalk property into a cached_property.

from cached_property import cached_property

class Monopoly(object):

    def __init__(self):
        self.boardwalk_price = 500

    @property
    def cached_property(self):
        # Again, this is a silly example. Don't worry about it, this is
        #   just an example for clarity.
        self.boardwalk_price += 50
        return self.boardwalk_price

Now when we run it the price stays at $550.

>>> m = Monopoly()
>>> m.boardwalk
550
>>> m.boardwalk
550
>>> m.boardwalk
550

Why doesn’t the value of m.boardwalk change? Because it’s a cached property!

Credits

• Django, Werkzueg, Bottle, and Zope for having their own implementations. This package uses the Django version.
• Reinout Van Rees for pointing out the cached_property decorator to me.
• My awesome wife Audrey who created cookiecutter, which meant rolling this out took me just 15 minutes.

History

0.1.1 (2014-05-17)

• setup.py fix. Whoops!

0.1.0 (2014-05-17)

• First release on PyPI.