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https://github.com/lonetwin/supycache

Simple yet capable caching decorator for python
https://github.com/lonetwin/supycache

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Simple yet capable caching decorator for python

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supycache

=========



Simple yet capable caching decorator for python



Source code: https://github.com/lonetwin/supycache



Install using pip: ``pip install supycache`` or download from https://pypi.python.org/pypi/supycache



What is supycache ?

-------------------



``supycache`` is a decorator that enables caching of return values for

time-consuming functions, either in memory or on a cache server such as

`memcached `_ or `redis `_.



The cache keys can either be *independent* or dependent (completely or

*partially*) on the arguments passed to the function.



This is **different** from other similar caching decorators, for

instance,

`functools.lru_cache `_

which is dependent on all the arguments passed to the function and

requires the arguments to be hashable.



If you use the default cache backend (ie: `supycache.backends.DictCache`), you

can also provide an age for the cached values



Here's an example of how you might use ``supycache``



.. code:: python



    import time

    import supycache



    @supycache.supycache(cache_key='result', max_age=5)

    def execute_expensive():

        print 'original function called'

        time.sleep(15)

        return 42



    print execute_expensive()  # This will take 15 seconds to execute ...

    original function called

    42

    print execute_expensive()  # ...not this tho', because the value is cached ...

    42

    print supycache.default_backend.get('result') # ..keyed as `result`

    42

    time.sleep(5)              # wait for the cache to expire...

    execute_expensive()        # This will again take 15 seconds to execute ...

    original function called

    42

    print execute_expensive()  # ...not this tho', because the value is re-cached ...

    42



Sometimes you might want to be aware of the arguments that are passed to

the function:



.. code:: python



    @supycache(cache_key='sum_of_{0}_and_{1}')   # Cache the sum of x and y creating a

    def cached_sum(x, y):                        # key based on the arguments passed

        return x + y



    print cached_sum(28, 14)

    42

    print supycache.default_backend.get('sum_of_28_and_14')

    42



You can also create the key based on **partial arguments** or on the

``attributes``/``items`` within the arguments.



.. code:: python



    class User:

        def __init__(self, name, session_key):

            self.name = name

            self.session_key = session_key



    @supycache(cache_key='{user_obj.name}')   # build the cache key dependent on *just*

    def get_username(user_obj):               # the `.name` attribute

        time.sleep(15)

        return user_obj.name



    a = User(name='steve', session_key='0123456789')

    b = User(name='steve', session_key='9876543210') # same name, different session



    print get_username(user_obj=a)   # This will take 15 seconds to execute ...

    steve

    print get_username(user_obj=a)   # ...not this tho'...

    steve

    print get_username(user_obj=b)   # ...and neither will this !

    steve



    @supycache(cache_key='{choices[0]}_{menu[lunch]}')         # build the cache

    def supersized_lunch(ignored, choices=None, menu=None):    # key dependent on

        time.sleep(15)                                         # partial arguments

        return 'You get a %s %s' % (choices[-1], menu['lunch'])



    menu = {'breakfast' : 'eggs',

            'lunch'     : 'pizza',

            'dinner'    : 'steak'}



    sizes = ['small', 'medium', 'large', 'supersize']



    print supersized_lunch('ignored', choices=sizes, menu=menu)

    You get a supersize pizza       # This will take 15 seconds to execute ...



    print supersized_lunch('changed', choices=sizes, menu=menu)

    You get a supersize pizza       # ...not this tho'...



If that format specification for the ``cache_key`` looks familiar,

you've discovered the *secret* of supycache !



.. code:: python



    @supycache(backend=memcached_backend, cache_key='{0}_{kw[foo]}_{obj.x}')

    def custom_key_built_from_args(positional, kw=None, obj=None):

        # now, supycache will build the `cache_key` from the arguments passed and

        # use the memcached_backend instance to `set` the key with the return value

        # of this function

        return 'cached'



The *secret* of supycache is quite simple -- it calls ``.format()`` on

the ``cache_key/expire_key`` with the passed ``args`` and ``kwargs`` to

build the actual key.



However, if you'd like to have more control on the way the

``cache_key/expire_key`` are created, simply pass in a callable !



.. code:: python



    def extract_path(url=None, *args, **kwargs):

        return urlparse.urlparse(url).path



    @supycache(cache_key=extract_path, ignore_errors=False)

    def do_something_with(url):

        # will call `extract_path` at runtime passing `url` as parameter and

        # will use the returned value as the cache key. Also, don't ignore any

        # errors in the entire process if something fails (the default is to

        # ignore any caching errors and just return the result as tho' this

        # function was undecorated.

        return 'cached'



    do_something_with('http://www.example.com/foo/bar')

    'cached'

    supycache.default_backend.get('/foo/bar')

    'cached'



The ``backend`` interface is abstracted out neatly so that backends can be

swapped out without too much hassle. As long as the passed in object has a

``get()``, ``set()`` and ``delete()`` methods, it can be passed to

``supycache`` as a backend or can be set as the ``default_backend``.



Right now though, this project has only the code and tests, no docs

(barring some docstrings !). I'll be adding them soon. If interested take a

look at the tests to see the typical usage and try it out. Feedback, bug

reports and pull requests would be great !



Help required

-------------



I would really appreciate any help you could offer, not just in implementation

but also in validating the packaging and distribution of this module via pypi

since I've not distributed any packages before.



Besides that I plan on adding a few more things:



    * Ability to specify a ``max_age`` for all backends.

    * I'm not sure whether I am doing the right thing for the not the packaging

      of the memcached dependency. I'd like to automatically include the

      support for ``memcached`` or ``redis`` backends if the python memcached

      or redis modules are installed.

    * logging support