shaypal5 / Cachier
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Cachier #######
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Persistent, stale-free, local and cross-machine caching for Python functions.
.. code-block:: python
from cachier import cachier import datetime
@cachier(stale_after=datetime.timedelta(days=3)) def foo(arg1, arg2): """foo now has a persistent cache, trigerring recalculation for values stored more than 3 days.""" return {'arg1': arg1, 'arg2': arg2}
.. role:: python(code) :language: python
.. contents::
.. section-numbering:
Installation
Install cachier
with:
.. code-block:: python
pip install cachier
For the latest version supporting Python 2.7 please use:
.. code-block:: python
pip install 'cachier==1.2.8'
Features
- Pure Python.
- Compatible with Python 3.5+ (and Python 2.7 up until version 1.2.8).
- Supported and
tested on Linux, OS X and Windows <https://travis-ci.org/shaypal5/cachier>
_. - A simple interface.
- Defining "shelf life" for cached values.
- Local caching using pickle files.
- Cross-machine caching using MongoDB.
- Thread-safety.
Cachier is NOT:
- Meant as a transient cache. Python's @lru_cache is better.
- Especially fast. It is meant to replace function calls that take more than... a second, say (overhead is around 1 millisecond).
Future features
- S3 core.
- Multi-core caching.
-
Cache replacement policies <https://en.wikipedia.org/wiki/Cache_replacement_policies>
_
Use
Cachier provides a decorator which you can wrap around your functions to give them a persistent cache. The positional and keyword arguments to the wrapped function must be hashable (i.e. Python's immutable built-in objects, not mutable containers). Also, notice that since objects which are instances of user-defined classes are hashable but all compare unequal (their hash value is their id), equal objects across different sessions will not yield identical keys.
Setting up a Cache
You can add a default, pickle-based, persistent cache to your function - meaning it will last across different Python kernels calling the wrapped function - by decorating it with the cachier
decorator (notice the ()
!).
.. code-block:: python
from cachier import cachier
@cachier() def foo(arg1, arg2): """Your function now has a persistent cache mapped by argument values!""" return {'arg1': arg1, 'arg2': arg2}
You can get the fully qualified path to the directory of cache files used by cachier
(~/.cachier
by default) by calling the cache_dpath()
function:
.. code-block:: python
foo.cache_dpath() "/home/bigus/.cachier/"
Resetting a Cache
The Cachier wrapper adds a clear_cache()
function to each wrapped function. To reset the cache of the wrapped function simply call this method:
.. code-block:: python
foo.clear_cache()
Cache Shelf Life
Setting Shelf Life
You can set any duration as the shelf life of cached return values of a function by providing a corresponding ``timedelta`` object to the ``stale_after`` parameter:
.. code-block:: python
import datetime
@cachier(stale_after=datetime.timedelta(weeks=2))
def bar(arg1, arg2):
return {'arg1': arg1, 'arg2': arg2}
Now when a cached value matching the given arguments is found the time of its calculation is checked; if more than ``stale_after`` time has since passed, the function will be run again for the same arguments and the new value will be cached and returned.
This is useful for lengthy calculations that depend on a dynamic data source.
Fuzzy Shelf Life
~~~~~~~~~~~~~~~~
Sometimes you may want your function to trigger a calculation when it encounters a stale result, but still not wait on it if it's not that critical. In that case, you can set ``next_time`` to ``True`` to have your function trigger a recalculation **in a separate thread**, but return the currently cached stale value:
.. code-block:: python
@cachier(next_time=True)
Further function calls made while the calculation is being performed will not trigger redundant calculations.
Working with unhashable arguments
---------------------------------
As mentioned above, the positional and keyword arguments to the wrapped function must be hashable (i.e. Python's immutable built-in objects, not mutable containers). To get around this limitation the ``hash_params`` parameter of the ``cachier`` decorator can be provided with a callable that gets the args and kwargs from the decorated function and returns a hash key for them.
.. code-block:: python
@cachier(hash_params=hash_my_custom_class)
def calculate_super_complex_stuff(custom_obj):
# amazing code goes here
Per-function call arguments
---------------------------
Cachier also accepts several keyword arguments in the calls of the function it wraps rather than in the decorator call, allowing you to modify its behaviour for a specific function call.
Ignore Cache
~~~~~~~~~~~~
You can have ``cachier`` ignore any existing cache for a specific function call by passing ``ignore_cache=True`` to the function call. The cache will neither be checked nor updated with the new return value.
.. code-block:: python
@cachier()
def sum(first_num, second_num):
return first_num + second_num
def main():
print(sum(5, 3, ignore_cache=True))
Overwrite Cache
~~~~~~~~~~~~~~~
You can have ``cachier`` overwrite an existing cache entry - if one exists - for a specific function call by passing ``overwrite_cache=True`` to the function call. The cache will not be checked but will be updated with the new return value.
Verbose Cache Call
You can have cachier
print out a detailed explanation of the logic of a specific call by passing verbose_cache=True
to the function call. This can be useful if you are not sure why a certain function result is, or is not, returned.
Cachier Cores
Pickle Core
The default core for Cachier is pickle based, meaning each function will store its cache is a separate pickle file in the ~/.cachier
directory. Naturally, this kind of cache is both machine-specific and user-specific.
You can configure cachier
to use another directory by providing the cache_dir
parameter with the path to that directory:
.. code-block:: python
@cachier(cache_dir='~/.temp/.cache')
You can slightly optimise pickle-based caching if you know your code will only be used in a single thread environment by setting:
.. code-block:: python
@cachier(pickle_reload=False)
This will prevent reading the cache file on each cache read, speeding things up a bit, while also nullifying inter-thread functionality (the code is still thread safe, but different threads will have different versions of the cache at times, and will sometime make unnecessary function calls).
MongoDB Core
You can set a MongoDB-based cache by assigning mongetter
with a callable that returns a pymongo.Collection
object with writing permissions:
.. code-block:: python
@cachier(mongetter=False)
This allows you to have a cross-machine, albeit slower, cache. This functionality requires that the installation of the pymongo
python package.
Contributing
Package author and current maintainer is Shay Palachy ([email protected]); You are more than welcome to approach him for help. Contributions are very welcomed.
Installing for development
Clone:
.. code-block:: bash
git clone [email protected]:shaypal5/cachier.git
Install in development mode with test dependencies:
.. code-block:: bash
cd cachier pip install -e ".[test]"
Running the tests
To run the tests, use:
.. code-block:: bash
python -m pytest --cov=cachier
Adding documentation
This project is documented using the numpy docstring conventions
, which were chosen as they are perhaps the most widely-spread conventions that are both supported by common tools such as Sphinx and result in human-readable docstrings (in my personal opinion, of course). When documenting code you add to this project, please follow these conventions
.
.. _numpy docstring conventions
: https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt
.. _these conventions
: https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt
Credits
Created by Shay Palachy ([email protected]).
.. Contributers (in chronological order of first commit):
.. * shaypal5 <https://github.com/shaypal5>
_ (Shay Palachy)
.. * j-chad <https://github.com/j-chad>
_ (Jackson)
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.. |PyPI-Versions| image:: https://img.shields.io/pypi/pyversions/cachier.svg :target: https://pypi.python.org/pypi/cachier
.. |Build-Status| image:: https://travis-ci.org/shaypal5/cachier.svg?branch=master :target: https://travis-ci.org/shaypal5/cachier
.. |LICENCE| image:: https://img.shields.io/pypi/l/cachier.svg :target: https://pypi.python.org/pypi/cachier
.. |Codecov| image:: https://codecov.io/github/shaypal5/cachier/coverage.svg?branch=master :target: https://codecov.io/github/shaypal5/cachier?branch=master
.. |Downloads| image:: https://pepy.tech/badge/cachier :target: https://pepy.tech/project/cachier :alt: PePy stats
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.. links: .. _pymongo: https://api.mongodb.com/python/current/ .. _watchdog: https://github.com/gorakhargosh/watchdog