CacheMan 1.0.0

A dependent cache manager

A Python interface for managing dependent caches.

‘Ba-Bop-Ba-Dop-Bop’

Description

This module acts as a dependency manager for caches and is ideal for instances where a program has many repeated computations that could be safely persisted. This usually entails a DB layer to house key value pairs. However, such a layer is sometimes overkill and managing a DB along with a project can be more effort than it’s worth. That’s where CacheMan comes in and provides an interface through which you can define savers, loaders, builders, and dependencies with disk-based defaults.

Dependencies

None – cacheman is a standalone module using only built-in libraries.

Features

• Drop in replacement for local memory dictionaries

• Default persistent pickle caches

• Non-persistent caching

• Cache load/save/delete hooks w/ defaults

• Cache validation hooks

• Cache builder hooks

• Dependent invalidation

How to use

Below are some simple examples for how to use the repository.

Setting up a simple persistent cache

from cacheman import cacher

manager = cacher.get_cache_manager() # Optional manager name argument can be used here
cache = manager.register_cache('my_simple_cache') # You now have a cache!
print cache.get('my_key') # `None` first run, 'my_value' if this code was executed earlier
cache['my_key'] = 'my_value'
manager.save_cache_contents('my_simple_cache') # Changes are now persisted to disk

Non-persistent caches

from cacheman import cacher

manager = cacher.get_cache_manager()
cache = manager.register_cache('my_simple_cache', persistent=False) # You cache won't save to disk
manager.save_cache_contents('my_cache') # This is a no-op

Registering hooks

from cacheman import cacher

def my_saver(cache_name, contents):
    print("Save requested on {} cache content: {}".format(cache_name, contents))

def my_loader(cache_name):
    return { 'load': 'faked' }

manager = cacher.get_cache_manager()
manager.register_saver('my_cache', my_saver)
manager.register_loader('my_cache', my_loader)

cache = manager.retrieve_cache('my_cache')
manager.save_cache_contents('my_cache') # Will print 'Save ... : { 'load': 'faked' }'
cache['new'] = 'real' # Add something to the cache
manager.save_cache_contents('my_cache') # Will print 'Save ... : { 'load': 'faked', 'new': 'real' }'

Dependent caches

from cacheman import cacher

manager = cacher.get_cache_manager()
manager.register_dependent_cache('edge_cache', 'root_cache')
root_cache = manager.register_cache('root_cache')

def get_processed_value():
    # Computes and caches 'processed' from root's 'raw' value
    edge = manager.retrieve_cache('edge_cache')
    processed = edge.get('processed')
    if processed is None:
        root = manager.retrieve_cache('root_cache')
        processed = (root.get('raw') or 0) * 5
        edge['processed'] = processed
    return processed

# A common problem with caching computed or dependent values:
print get_processed_value() # 0 without raw value
manager.retrieve_cache('root_cache')['raw'] = 1
print get_processed_value() # still 0 because it's cache in edge

# Now we use cache invalidation to tell downstream caches they're no longer valid
manager.invalidate_cache('root_cache') # Invalidates dependent caches
print manager.retrieve_cache('edge_cache') # Prints {} even though we only invalidated 'root_cache'
manager.retrieve_cache('root_cache')['raw'] = 1
print get_processed_value() # Now 5 because the edge was cleared before the request

Setting cache directory

manager = cacher.get_cache_manager()
# Default cache directory is '/tmp/general_cacher' or 'user\appadata\local\temp\general_cache'
manager.set_cache_directory('secret/cache/location') # All pickle caches now save here

cache = manager.register_cache('my_cache')
cache['new'] = 'real' # Add something to the cache
manager.save_cache_contents('my_cache') # Will save contents to 'secret/cache/location/my_cache.pkl'

Navigating the Repo

cacheman

Package wrapper for the repo.

tests

All unit tests for the repo.

Language Preferences

• Google Style Guide

• Object Oriented (with a few exceptions)

Author

Author(s): Matthew Seal

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