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Metadata-Version: 1.1 Name: cached-property Version: 1.3.0 Summary: A decorator for caching properties in classes. Home-page: https://github.com/pydanny/cached-property Author: Daniel Greenfeld Author-email: pydanny@gmail.com License: BSD Description: =============================== cached-property =============================== .. image:: https://img.shields.io/pypi/v/cached-property.svg :target: https://pypi.python.org/pypi/cached-property .. image:: https://img.shields.io/travis/pydanny/cached-property/master.svg :target: https://travis-ci.org/pydanny/cached-property A decorator for caching properties 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! .. code-block:: python 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: .. code-block:: python >>> monopoly = Monopoly() >>> monopoly.boardwalk 550 >>> monopoly.boardwalk 600 Let's convert the boardwalk property into a ``cached_property``. .. code-block:: python 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. .. code-block:: python >>> 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: .. code-block:: python >>> monopoly = Monopoly() >>> monopoly.boardwalk 550 >>> monopoly.boardwalk 550 >>> # invalidate the cache >>> del monopoly.__dict__['boardwalk'] >>> # request the boardwalk property again >>> monopoly.boardwalk 600 >>> monopoly.boardwalk 600 Working with Threads --------------------- What if a whole bunch of people want to stay at Boardwalk all at once? This means using threads, which unfortunately causes problems with the standard ``cached_property``. In this case, switch to using the ``threaded_cached_property``: .. code-block:: python from cached_property import threaded_cached_property class Monopoly(object): def __init__(self): self.boardwalk_price = 500 @threaded_cached_property def boardwalk(self): """threaded_cached_property is really nice for when no one waits for other people to finish their turn and rudely start rolling dice and moving their pieces.""" sleep(1) self.boardwalk_price += 50 return self.boardwalk_price Now use it: .. code-block:: python >>> from threading import Thread >>> from monopoly import Monopoly >>> monopoly = Monopoly() >>> threads = [] >>> for x in range(10): >>> thread = Thread(target=lambda: monopoly.boardwalk) >>> thread.start() >>> threads.append(thread) >>> for thread in threads: >>> thread.join() >>> self.assertEqual(m.boardwalk, 550) Timing out the cache -------------------- Sometimes you want the price of things to reset after a time. Use the ``ttl`` versions of ``cached_property`` and ``threaded_cached_property``. .. code-block:: python import random from cached_property import cached_property_with_ttl class Monopoly(object): @cached_property_with_ttl(ttl=5) # cache invalidates after 5 seconds def dice(self): # I dare the reader to implement a game using this method of 'rolling dice'. return random.randint(2,12) Now use it: .. code-block:: python >>> monopoly = Monopoly() >>> monopoly.dice 10 >>> monopoly.dice 10 >>> from time import sleep >>> sleep(6) # Sleeps long enough to expire the cache >>> monopoly.dice 3 >>> monopoly.dice 3 Note: The ``ttl`` tools do not reliably allow the clearing of the cache. This is why they are broken out into seperate tools. See https://github.com/pydanny/cached-property/issues/16. 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. * @tinche for pointing out the threading issue and providing a solution. * @bcho for providing the time-to-expire feature .. _`@audreyr`: https://github.com/audreyr .. _`cookiecutter`: https://github.com/audreyr/cookiecutter History ------- 1.3.0 (2015-11-24) ++++++++++++++++++ * Added official support for Python 3.5, thanks to @pydanny and @audreyr * Removed confusingly placed lock from example, thanks to @ionelmc * Corrected invalidation cache documentation, thanks to @proofit404 * Updated to latest Travis-CI environment, thanks to @audreyr 1.2.0 (2015-04-28) ++++++++++++++++++ * Overall code and test refactoring, thanks to @gsakkis * Allow the del statement for resetting cached properties with ttl instead of del obj._cache[attr], thanks to @gsakkis. * Uncovered a bug in PyPy, https://bitbucket.org/pypy/pypy/issue/2033/attributeerror-object-attribute-is-read, thanks to @gsakkis * Fixed threaded_cached_property_with_ttl to actually be thread-safe, thanks to @gsakkis 1.1.0 (2015-04-04) ++++++++++++++++++ * Regression: As the cache was not always clearing, we've broken out the time to expire feature to its own set of specific tools, thanks to @pydanny * Fixed typo in README, thanks to @zoidbergwill 1.0.0 (2015-02-13) ++++++++++++++++++ * Added timed to expire feature to ``cached_property`` decorator. * Backwards incompatiblity: Changed ``del monopoly.boardwalk`` to ``del monopoly['boardwalk']`` in order to support the new TTL feature. 0.1.5 (2014-05-20) ++++++++++++++++++ * Added threading support with new ``threaded_cached_property`` decorator * Documented cache invalidation * Updated credits * Sourced the bottle implementation 0.1.4 (2014-05-17) ++++++++++++++++++ * 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. Keywords: cached-property Platform: UNKNOWN Classifier: Development Status :: 5 - Production/Stable Classifier: Intended Audience :: Developers Classifier: License :: OSI Approved :: BSD License Classifier: Natural Language :: English Classifier: Programming Language :: Python :: 2 Classifier: Programming Language :: Python :: 2.6 Classifier: Programming Language :: Python :: 2.7 Classifier: Programming Language :: Python :: 3 Classifier: Programming Language :: Python :: 3.3 Classifier: Programming Language :: Python :: 3.4 Classifier: Programming Language :: Python :: 3.5