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A cached-property for decorating methods in classes.

Project Description

https://badge.fury.io/py/cached-property.png https://travis-ci.org/pydanny/cached-property.png?branch=master https://pypip.in/d/cached-property/badge.png

A cached-property for decorating methods in classes.

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

Let’s define a class with an expensive property. Every time you stay there the price goes up by $50!

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:

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

    @cached_property
    def boardwalk(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.

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

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

Invalidating the Cache

Results of cached functions can be invalidated by outside forces. Let’s demonstrate how to force the cache to invalidate:

>>> monopoly = Monopoly()
>>> monopoly.boardwalk
550
>>> monopoly.boardwalk
550
>>> # invalidate the cache
>>> del m.boardwalk
>>> # request the boardwalk property again
>>> m.boardwalk
600
>>> m.boardwalk
600

Credits

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

History

0.1.4 (2014-05-18)

  • Fix the dang-blarged py_modules argument.

0.1.3 (2014-05-17)

  • Removed import of package into setup.py

0.1.2 (2014-05-17)

  • Documentation fixes. Not opening up a RTFD instance for this because it’s so simple to use.

0.1.1 (2014-05-17)

  • setup.py fix. Whoops!

0.1.0 (2014-05-17)

  • First release on PyPI.

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Filename, size & hash SHA256 hash help File type Python version Upload date
cached_property-0.1.4-py2.py3-none-any.whl (4.8 kB) Copy SHA256 hash SHA256 Wheel 3.3 May 18, 2014
cached-property-0.1.4.tar.gz (5.7 kB) Copy SHA256 hash SHA256 Source None May 18, 2014

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