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A dependent cache manager

Project description

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.

By default all caches will auto save when 10k changes occur over 60 seconds, 10 changes occur over 300 seconds (but after 60 seconds), or 1 change occurs within 900 seconds (after 300 seconds). This behavior can be changed by instantiating an AutoSyncCache from the autosync submodule.

Dependencies

allset – for automatic module importing

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
  • Auto-Syncing caches

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'
cache.save() # Changes are now persisted to disk
manager.save_cache_contents('my_simple_cache') # Alternative way to save a cache

Non-persistent caches

from cacheman import cacher

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

Registering hooks

from cacheman import cacher
from cacheman import cachewrap

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()

cache = cachewrap.PersistentCache('my_cache', saver=my_saver, loader=my_loader)
# Can also use manager to set savers/loaders
#manager.retrieve_cache('my_cache')
#manager.register_saver('my_cache', my_saver)
#manager.register_loader('my_cache', my_loader)

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

Dependent caches

from cacheman import cacher

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

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

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

# Now we use cache invalidation to tell downstream caches they're no longer valid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

Setting cache directory

from cacheman import cacher

manager = cacher.get_cache_manager()
# Default cache directory is '/tmp/general_cacher' or 'user\appadata\local\temp\general_cache'
manager.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
cache.save('my_cache') # Will save contents to 'secret/cache/location/my_cache.pkl'

Language Preferences

  • Google Style Guide
  • Object Oriented (with a few exceptions)

TODO

V2.1 * cPickle with fallback to pickle by default * Better argument checks

Author

Author(s): Matthew Seal

© Copyright 2013, OpenGov

Project details


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