Metadata-Version: 1.1
Name: cached-property
Version: 1.5.1
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
        
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            :target: https://github.com/ambv/black
            :alt: Code style: black        
        
        
        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)
        
        
        Working with async/await (Python 3.5+)
        --------------------------------------
        
        The cached property can be async, in which case you have to use await
        as usual to get the value. Because of the caching, the value is only
        computed once and then cached:
        
        .. code-block:: python
        
            from cached_property import cached_property
        
            class Monopoly(object):
        
                def __init__(self):
                    self.boardwalk_price = 500
        
                @cached_property
                async def boardwalk(self):
                    self.boardwalk_price += 50
                    return self.boardwalk_price
        
        Now use it:
        
        .. code-block:: python
        
            >>> async def print_boardwalk():
            ...     monopoly = Monopoly()
            ...     print(await monopoly.boardwalk)
            ...     print(await monopoly.boardwalk)
            ...     print(await monopoly.boardwalk)
            >>> import asyncio
            >>> asyncio.get_event_loop().run_until_complete(print_boardwalk())
            550
            550
            550
        
        Note that this does not work with threading either, most asyncio
        objects are not thread-safe. And if you run separate event loops in
        each thread, the cached version will most likely have the wrong event
        loop. To summarize, either use cooperative multitasking (event loop)
        or threading, but not both at the same time.
        
        
        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 originally used an implementation that matched 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
        
        Support This Project
        ---------------------------
        
        This project is maintained by volunteers. Support their efforts by spreading the word about:
        
        .. image:: https://cdn.shopify.com/s/files/1/0304/6901/t/2/assets/logo.png?8399580890922549623
           :name: Two Scoops Press
           :align: center
           :alt: Two Scoops Press
           :target: https://www.twoscoopspress.com
        
        
        
        
        History
        -------
        
        1.5.1 (2018-08-05)
        ++++++++++++++++++
        
        * Added formal support for Python 3.7
        * Removed formal support for Python 3.3
        
        1.4.3  (2018-06-14)
        +++++++++++++++++++
        
        * Catch SyntaxError from asyncio import on older versions of Python, thanks to @asottile
        
        1.4.2 (2018-04-08)
        ++++++++++++++++++
        
        * Really fixed tests, thanks to @pydanny
        
        1.4.1 (2018-04-08)
        ++++++++++++++++++
        
        * Added conftest.py to manifest so tests work properly off the tarball, thanks to @dotlambda
        * Ensured new asyncio tests didn't break Python 2.7 builds on Debian, thanks to @pydanny
        * Code formatting via black, thanks to @pydanny and @ambv
        
        
        1.4.0 (2018-02-25)
        ++++++++++++++++++
        
        * Added asyncio support, thanks to @vbraun
        * Remove Python 2.6 support, whose end of life was 5 years ago, thanks to @pydanny
        
        
        1.3.1 (2017-09-21)
        ++++++++++++++++++
        
        * Validate for Python 3.6
        
        
        1.3.0 (2015-11-24)
        ++++++++++++++++++
        
        * Drop some non-ASCII characters from HISTORY.rst, thanks to @AdamWill
        * 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 :: 2.7
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.4
Classifier: Programming Language :: Python :: 3.5
Classifier: Programming Language :: Python :: 3.6
Classifier: Programming Language :: Python :: 3.7
