User Guide

This section covers the main features of aiohttp-client-cache.

Installation

Install with pip:

pip install aiohttp-client-cache

Or with conda, if you prefer:

conda install -c conda-forge aiohttp-client-cache

Requirements

  • Requires python 3.7+.

  • You may need additional dependencies depending on which backend you want to use. To install with extra dependencies for all supported Cache Backends:

    pip install aiohttp-client-cache[backends]
    

Optional Setup Steps

  • See Security for recommended setup steps for more secure cache serialization.

  • See Contributing Guide for setup steps for local development.

General Usage

CachedSession can be used as a drop-in replacement for aiohttp.ClientSession. Basic usage looks like this:

>>> from aiohttp_client_cache import CachedSession
>>>
>>> async with CachedSession() as session:
>>>     await session.get('http://httpbin.org/delay/1')

Any ClientSession method can be used (but see HTTP Methods section below for config details):

>>> await session.request('GET', 'http://httpbin.org/get')
>>> await session.head('http://httpbin.org/get')

Caching can be temporarily disabled with CachedSession.disabled():

>>> with session.disabled():
...     await session.get('http://httpbin.org/get')

The best way to clean up your cache is through Cache Expiration, but you can also clear out everything at once with CacheBackend.clear():

>>> await session.cache.clear()

Cache Options

A number of options are available to modify which responses are cached and how they are cached.

HTTP Methods

By default, only GET and HEAD requests are cached. To cache additional HTTP methods, specify them with allowed_methods. For example, caching POST requests can be used to ensure you don’t send the same data multiple times:

>>> cache = SQLiteBackend(allowed_methods=('GET', 'POST'))
>>> async with CachedSession(cache=cache) as session:
>>>     await session.post('http://httpbin.org/post', json={'param': 'value'})

Status Codes

By default, only responses with a 200 status code are cached. To cache additional status codes, specify them with allowed_codes

>>> cache = SQLiteBackend(allowed_codes=(200, 418))
>>> async with CachedSession(cache=cache) as session:
>>>     await session.get('http://httpbin.org/teapot')

Request Parameters

By default, all request parameters are taken into account when caching responses. In some cases, there may be request parameters that don’t affect the response data, for example authentication tokens or credentials. If you want to ignore specific parameters, specify them with ignored_parameters:

>>> cache = SQLiteBackend(ignored_parameters=['auth-token'])
>>> async with CachedSession(cache=cache) as session:
>>>     # Only the first request will be sent
>>>     await session.get('http://httpbin.org/get', params={'auth-token': '2F63E5DF4F44'})
>>>     await session.get('http://httpbin.org/get', params={'auth-token': 'D9FAEB3449D3'})

Request Headers

In some cases, different headers may result in different response data, so you may want to cache them separately. To enable this, use include_headers:

>>> cache = SQLiteBackend(include_headers=True)
>>> async with CachedSession(cache=cache) as session:
>>>     # Both of these requests will be sent and cached separately
>>>     await session.get('http://httpbin.org/headers', {'Accept': 'text/plain'})
>>>     await session.get('http://httpbin.org/headers', {'Accept': 'application/json'})

Cache Expiration

By default, cached responses will be stored indefinitely. You can initialize the cache with an expire_after value to specify how long responses will be cached.

Expiration Values

expire_after can be any of the following:

  • -1: Never expire

  • 0 Expire immediately, e.g. skip writing to the cache

  • A positive number (in seconds)

  • A timedelta

  • A datetime

Examples:

>>> # Set expiration for the session using a value in seconds
>>> cache = SQLiteBackend(expire_after=360)

>>> # To specify a different unit of time, use a timedelta
>>> from datetime import timedelta
>>> cache = SQLiteBackend(expire_after=timedelta(days=30))

>>> # Update an existing session to disable expiration (i.e., store indefinitely)
>>> session.expire_after = -1

URL Patterns

You can use urls_expire_after to set different expiration values for different requests, based on URL glob patterns. This allows you to customize caching based on what you know about the resources you’re requesting. For example, you might request one resource that gets updated frequently, another that changes infrequently, and another that never changes. Example:

>>> cache = SQLiteBackend(
...     urls_expire_after={
...         '*.site_1.com': 30,
...         'site_2.com/resource_1': 60 * 2,
...         'site_2.com/resource_2': 60 * 60 * 24,
...         'site_2.com/static': -1,
...     }
... )

Notes:

  • urls_expire_after should be a dict in the format {'pattern': expire_after}

  • expire_after accepts the same types as CacheBackend.expire_after

  • Patterns will match request base URLs, so the pattern site.com/resource/ is equivalent to http*://site.com/resource/**

  • If there is more than one match, the first match will be used in the order they are defined

  • If no patterns match a request, CacheBackend.expire_after will be used as a default.

Cache-Control

Warning

This is not intended to be a thorough or strict implementation of header-based HTTP caching, e.g. according to RFC 2616.

Optional support is included for a simplified subset of Cache-Control and other cache headers in both requests and responses. To enable this behavior, use the cache_control backend option:

>>> cache = SQLiteBackend(cache_control=True)

Supported request headers:

  • Cache-Control: max-age: Used as the expiration time in seconds

  • Cache-Control: no-cache: Skips reading response data from the cache

  • Cache-Control: no-store: Skips reading and writing response data from/to the cache

Supported response headers:

  • Cache-Control: max-age: Used as the expiration time in seconds

  • Cache-Control: no-store Skips writing response data to the cache

  • Expires: Used as an absolute expiration time

Notes:

  • Unlike a browser or proxy cache, max-age=0 does not currently clear previously cached responses.

  • If enabled, Cache-Control directives will take priority over any other expire_after value. See Expiration Precedence for the full order of precedence.

Removing Expired Responses

For better performance, expired responses won’t be removed immediately, but will be removed (or replaced) the next time they are requested. To manually clear all expired responses, use CachedSession.remove_expired_responses():

>>> session.remove_expired_responses()

You can also apply a different expire_after to previously cached responses, which will revalidate the cache with the new expiration time:

>>> session.remove_expired_responses(expire_after=timedelta(days=30))

Expiration Precedence

Expiration can be set on a per-session, per-URL, or per-request basis, in addition to cache headers. When there are multiple values provided for a given request, the following order of precedence is used:

  1. Cache-Control request headers (if enabled)

  2. Cache-Control response headers (if enabled)

  3. Per-request expiration (expire_after argument for CachedSession.request())

  4. Per-URL expiration (urls_expire_after argument for CachedSession)

  5. Per-session expiration (expire_after argument for CacheBackend)

Cache Inspection

Here are some ways to get additional information out of the cache session, backend, and responses:

Response Attributes

The following attributes are available on both cached and new responses returned from CachedSession:

  • from_cache: indicates if the response came from the cache

  • created_at: datetime of when the cached response was created or last updated

  • expires: datetime after which the cached response will expire

  • is_expired: indicates if the cached response is expired (if an old response was returned due to a request error)

Examples:

>>> from aiohttp_client_cache import CachedSession
>>> session = CachedSession(expire_after=timedelta(days=1))

>>> # Placeholders are added for non-cached responses
>>> r = await session.get('http://httpbin.org/get')
>>> print(r.from_cache, r.created_at, r.expires, r.is_expired)
False None None None

>>> # Values will be populated for cached responses
>>> r = await session.get('http://httpbin.org/get')
>>> print(r.from_cache, r.created_at, r.expires, r.is_expired)
True 2021-01-01 18:00:00 2021-01-02 18:00:00 False

Cache Contents

You can use CachedSession.cache.urls() to see all URLs currently in the cache:

>>> session = CachedSession(cache=SQLiteCache())
>>> print(session.cache.urls)
['https://httpbin.org/get', 'https://httpbin.org/stream/100']

If needed, you can get more details on cached responses via CachedSession.cache.responses, which is a interface to the cache backend. See CachedResponse for a full list of attributes available.

For example, if you wanted to to see all URLs requested with a specific method:

>>> post_urls = [
>>>     response.url async for response in session.cache.responses.values()
>>>     if response.method == 'POST'
>>> ]

You can also inspect CachedSession.cache.redirects, which maps redirect URLs to keys of the responses they redirect to.

Other Cache Features

Custom Response Filtering

If you need more advanced behavior for determining what to cache, you can provide a custom filtering function via the filter_fn param. This can by any function that takes a aiohttp.ClientResponse object and returns a boolean indicating whether or not that response should be cached. It will be applied to both new responses (on write) and previously cached responses (on read). Example:

>>> from sys import getsizeof
>>> from aiohttp_client_cache import CachedSession, SQLiteCache
>>>
>>> def filter_by_size(response):
>>>     """Don't cache responses with a body over 1 MB"""
>>>     return getsizeof(response._body) <= 1024 * 1024
>>>
>>> cache = SQLiteCache(filter_fn=filter_by_size)

Library Compatibility

This library works by extending aiohttp.ClientSession, and there are other libraries out there that do the same. For that reason a mixin class is included, so you can create a custom class with behavior from multiple aiohttp-based libraries:

>>> from aiohttp import ClientSession
>>> from aiohttp_client_cache import CacheMixin
>>> from some_other_library import CustomMixin
>>>
>>> class CustomSession(CacheMixin, CustomMixin, ClientSession):
...     """Session with features from both aiohttp_client_cache and some_other_library"""