A cached-property for decorating methods in classes.
Project Description
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 |
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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 |