This document describes the current stable version of Celery (4.4). For development docs, go here.

Source code for celery.backends.cache

# -*- coding: utf-8 -*-
"""Memcached and in-memory cache result backend."""
from __future__ import absolute_import, unicode_literals

from kombu.utils.encoding import bytes_to_str, ensure_bytes
from kombu.utils.objects import cached_property

from celery.exceptions import ImproperlyConfigured
from celery.five import PY3
from celery.utils.functional import LRUCache

from .base import KeyValueStoreBackend

__all__ = ('CacheBackend',)

_imp = [None]

The Memcached backend requires either pylibmc or python-memcached.\

The cache backend {0!r} is unknown,
Please use one of the following backends instead: {1}\

def import_best_memcache():
    if _imp[0] is None:
        is_pylibmc, memcache_key_t = False, ensure_bytes
            import pylibmc as memcache
            is_pylibmc = True
        except ImportError:
                import memcache  # noqa
            except ImportError:
                raise ImproperlyConfigured(REQUIRES_BACKEND)
        if PY3:  # pragma: no cover
            memcache_key_t = bytes_to_str
        _imp[0] = (is_pylibmc, memcache, memcache_key_t)
    return _imp[0]

def get_best_memcache(*args, **kwargs):
    # pylint: disable=unpacking-non-sequence
    #   This is most definitely a sequence, but pylint thinks it's not.
    is_pylibmc, memcache, key_t = import_best_memcache()
    Client = _Client = memcache.Client

    if not is_pylibmc:
        def Client(*args, **kwargs):  # noqa
            kwargs.pop('behaviors', None)
            return _Client(*args, **kwargs)

    return Client, key_t

class DummyClient(object):

    def __init__(self, *args, **kwargs):
        self.cache = LRUCache(limit=5000)

    def get(self, key, *args, **kwargs):
        return self.cache.get(key)

    def get_multi(self, keys):
        cache = self.cache
        return {k: cache[k] for k in keys if k in cache}

    def set(self, key, value, *args, **kwargs):
        self.cache[key] = value

    def delete(self, key, *args, **kwargs):
        self.cache.pop(key, None)

    def incr(self, key, delta=1):
        return self.cache.incr(key, delta)

    def touch(self, key, expire):

backends = {
    'memcache': get_best_memcache,
    'memcached': get_best_memcache,
    'pylibmc': get_best_memcache,
    'memory': lambda: (DummyClient, ensure_bytes),

[docs]class CacheBackend(KeyValueStoreBackend): """Cache result backend.""" servers = None supports_autoexpire = True supports_native_join = True implements_incr = True def __init__(self, app, expires=None, backend=None, options=None, url=None, **kwargs): options = {} if not options else options super(CacheBackend, self).__init__(app, **kwargs) self.url = url self.options = dict(, **options) self.backend = url or backend or if self.backend: self.backend, _, servers = self.backend.partition('://') self.servers = servers.rstrip('/').split(';') self.expires = self.prepare_expires(expires, type=int) try: self.Client, self.key_t = backends[self.backend]() except KeyError: raise ImproperlyConfigured(UNKNOWN_BACKEND.format( self.backend, ', '.join(backends))) self._encode_prefixes() # rencode the keyprefixes
[docs] def get(self, key): return self.client.get(key)
[docs] def mget(self, keys): return self.client.get_multi(keys)
[docs] def set(self, key, value): return self.client.set(key, value, self.expires)
[docs] def delete(self, key): return self.client.delete(key)
def _apply_chord_incr(self, header_result, body, **kwargs): chord_key = self.get_key_for_chord( self.client.set(chord_key, 0, time=self.expires) return super(CacheBackend, self)._apply_chord_incr( header_result, body, **kwargs)
[docs] def incr(self, key): return self.client.incr(key)
[docs] def expire(self, key, value): return self.client.touch(key, value)
[docs] @cached_property def client(self): return self.Client(self.servers, **self.options)
def __reduce__(self, args=(), kwargs=None): kwargs = {} if not kwargs else kwargs servers = ';'.join(self.servers) backend = '{0}://{1}/'.format(self.backend, servers) kwargs.update( {'backend': backend, 'expires': self.expires, 'options': self.options}) return super(CacheBackend, self).__reduce__(args, kwargs)
[docs] def as_uri(self, *args, **kwargs): """Return the backend as an URI. This properly handles the case of multiple servers. """ servers = ';'.join(self.servers) return '{0}://{1}/'.format(self.backend, servers)