cashews 0.2.1

cache tools with async power

CASHEWS 🥔

Async cache utils with simple api to build fast and reliable applications

pip install cashews[redis]

Why

Cache plays significant role in modern applications and everybody wanna use all power of async programming and cache.. There are a few advance techniques with cache and async programming that can help you to build simple, fast, scalable and reliable applications. Caches

Features

• Decorator base api, just decorate and play
• Cache invalidation by time, 'ttl' a required parameter to avoid storage overflow and endless cache
• Support Multi backend (Memory, Redis, memcache by request)
• Can cache any objects securely with pickle (use hash key).
• Simple configuring and API

API

• simple cache
• fail cache
• hit-rate cache
• perf-rate cache
• rate-limit
• cache with early expiration/rebuilding
• locked cache
• api for key storage/backend

Usage

Configure

Cache object is a single object that can be configured in one place by url::

from cashews import cache

cache.setup("redis://0.0.0.0/?db=1&create_connection_timeout=0.5&safe=0&hash_key=my_sicret&enable=1")
or
cache.setup("redis://0.0.0.0/", db=1, create_connection_timeout=0.5, safe=False, hash_key=b"my_key", enable=True)
or
cache.setup("mem://") # for inmemory cache

if you dont like global objects or prefer more manageable way you can work with cache class

from cashews import Cache

cache = Cache()
cache.setup("mem://")

Simple cache

Typical cache strategy: execute, store and return cached value till expiration::

from cashews import cache
from datetime import timedelta

@cache(ttl=timedelta(hours=3))
def long_running_function(arg, kward):
    ...

:param ttl: seconds in int value or as timedelta object to define time to store objects :param func_args: arguments of call that will be used in key, can be tuple or dict with argument name as a key and callable object as a transform function for value of this argument

@cache(ttl=100, func_args=("arg", "token"))
def long_running_function(arg, user: User, token: str = "token"):
    ...

long_running_function("name", user=user, token="qdfrevt")  # key will be like "long_running_function:arg:name:token:qdfrevt

But what if we want to user argument define a cache key or want to hide token from cache

@cache(ttl=100, func_args={"arg": True, "token": get_md5, "user": attrgetter("uid")})
def long_running_function(arg, user: User, token: str = "token"):
    ...

long_running_function("name", user=user, token="qdfrevt")  # key will be like "long_running_function:arg:name:token:7ea802f0544ff108aace43e2d3752a28:user:51e6da60-2553-45ec-9e56-d9538b9614c8

:param key: custom cache key, may contain alias to args or kwargs passed to a call (like 'key_{token}/{arg}{user}') :param condition: callable object that determines whether the result will be saved or not :param prefix: custom prefix for key

Fail cache

Return cache result (at list 1 call of function call should be succeed) if call raised one of the given exceptions,

:param ttl: seconds in int or as timedelta object to store a result :param exceptions: exceptions at which returned cache result :param func_args: see simple cache params :param key: custom cache key, may contain alias to args or kwargs passed to a call :param prefix: custom prefix for key, default "fail"

Example

from cashews import cache  # or from cashews import fail

@cache.fail(ttl=timedelta(hours=2))
async def get(name):
    value = await api_call()
    return {"status": value}

Hit cache

Cache call results and drop cache after given numbers of call 'cache_hits'

:param ttl: seconds in int or as timedelta object to store a result :param cache_hits: number of cache hits till cache will dropped :param update_before: number of cache hits before cache will update :param func_args: see simple cache params :param key: custom cache key, may contain alias to args or kwargs passed to a call :param condition: callable object that determines whether the result will be saved or not :param prefix: custom prefix for key, default "hit"

Example

from cashews import cache  # or from cashews import hit

@cache.hit(ttl=timedelta(hours=2), cache_hits=100, update_before=2)
async def get(name):
    ...

Performance downgrade cache

Trace time execution of target and enable cache if it downgrade to given condition

:param ttl: seconds in int or as timedelta object to store a result :param func_args: see simple cache params :param key: custom cache key, may contain alias to args or kwargs passed to a call :param trace_size: the number of calls that are involved :param perf_condition: callable object that determines whether the result will be cached, default if doubled mean value of time execution less then current :param prefix: custom prefix for key, default 'perf'

from cashews import cache   # or from cashews import perf

@cache.perf(ttl=timedelta(hours=2))
async def get(name):
    value = await api_call()
    return {"status": value}

Locked

Cache strategy that try to solve Cache stampede problem (https://en.wikipedia.org/wiki/Cache_stampede), Lock following function calls till it be cached Can guarantee one function call for given ttl

:param ttl: seconds in int or timedelta object to store a result :param func_args: see simple cache params :param key: custom cache key, may contain alias to args or kwargs passed to a call :param lock_ttl: seconds in int or timedelta object to lock wrapped function call (should be more than function execution time) :param prefix: custom prefix for key, default 'early'

from cashews import cache  # or from cashews import locked

@cache.locked(ttl=timedelta(minutes=10))
async def get(name):
    value = await api_call()
    return {"status": value}

Early

Cache strategy that try to solve Cache stampede problem (https://en.wikipedia.org/wiki/Cache_stampede), With a hot cache recalculate a result in background near expiration time Warning! Not good at cold cache

:param ttl: seconds in int or as timedelta object to store a result :param func_args: see simple cache params :param key: custom cache key, may contain alias to args or kwargs passed to a call :param condition: callable object that determines whether the result will be saved or not :param prefix: custom prefix for key, default 'early'

Rate limit

Rate limit for function call. Do not call function if rate limit is reached, and call given action

:param limit: number of calls :param period: Period :param ttl: time to ban, default == period :param func_args: see simple cache params :param action: call when rate limit reached, default raise RateLimitException :param prefix: custom prefix for key, default 'rate_limit'

from cashews import cache  # or from cashews import rate_limit

# no more then 10 calls per minute or ban for 10 minutes
@cache.rate_limit(limit=10, period=timedelta(minutes=1) ttl=timedelta(minutes=10))
async def get(name):
    return {"status": value}

Basic api

There are 11 basic methods to work with key-storage::

from cashews import cache

cache.setup("mem://")

await cache.set(key="key", value={"any": True}, expire=60, exist=None)  # -> bool
await cache.get("key")  # -> Any
await cache.incr("key") # -> int
await cache.delete("key")
await cache.expire("key", timeout=10)
await cache.ping(message=None)  # -> bytes
await cache.clear()
await cache.set_lock("key", value="value", expire=60)  # -> bool
await cache.is_locked("key", wait=60)  # -> bool
await cache.unlock("key", "value")  # -> bool
async with cache.lock("key", expire=10):

todos:

cache invalidation solution