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"""
Caching framework.
This package defines set of cache backends that all conform to a simple API.
In a nutshell, a cache is a set of values -- which can be any object that
may be pickled -- identified by string keys. For the complete API, see
the abstract BaseCache class in django.core.cache.backends.base.
Client code should not access a cache backend directly; instead it should
either use the "cache" variable made available here, or it should use the
get_cache() function made available here. get_cache() takes a backend URI
(e.g. "memcached://127.0.0.1:11211/") and returns an instance of a backend
cache class.
See docs/topics/cache.txt for information on the public API.
"""
from django.conf import settings
from django.core import signals
from django.core.cache.backends.base import (
InvalidCacheBackendError, CacheKeyWarning, BaseCache)
from django.core.exceptions import ImproperlyConfigured
from django.utils import importlib
try:
# The mod_python version is more efficient, so try importing it first.
from mod_python.util import parse_qsl
except ImportError:
try:
# Python 2.6 and greater
from urlparse import parse_qsl
except ImportError:
# Python 2.5. Works on Python 2.6 but raises PendingDeprecationWarning
from cgi import parse_qsl
__all__ = [
'get_cache', 'cache', 'DEFAULT_CACHE_ALIAS'
]
# Name for use in settings file --> name of module in "backends" directory.
# Any backend scheme that is not in this dictionary is treated as a Python
# import path to a custom backend.
BACKENDS = {
'memcached': 'memcached',
'locmem': 'locmem',
'file': 'filebased',
'db': 'db',
'dummy': 'dummy',
}
DEFAULT_CACHE_ALIAS = 'default'
def parse_backend_uri(backend_uri):
"""
Converts the "backend_uri" into a cache scheme ('db', 'memcached', etc), a
host and any extra params that are required for the backend. Returns a
(scheme, host, params) tuple.
"""
if backend_uri.find(':') == -1:
raise InvalidCacheBackendError("Backend URI must start with scheme://")
scheme, rest = backend_uri.split(':', 1)
if not rest.startswith('//'):
raise InvalidCacheBackendError("Backend URI must start with scheme://")
host = rest[2:]
qpos = rest.find('?')
if qpos != -1:
params = dict(parse_qsl(rest[qpos+1:]))
host = rest[2:qpos]
else:
params = {}
if host.endswith('/'):
host = host[:-1]
return scheme, host, params
if not settings.CACHES:
legacy_backend = getattr(settings, 'CACHE_BACKEND', None)
if legacy_backend:
import warnings
warnings.warn(
"settings.CACHE_* is deprecated; use settings.CACHES instead.",
DeprecationWarning
)
else:
# The default cache setting is put here so that we
# can differentiate between a user who has provided
# an explicit CACHE_BACKEND of locmem://, and the
# default value. When the deprecation cycle has completed,
# the default can be restored to global_settings.py
settings.CACHE_BACKEND = 'locmem://'
# Mapping for new-style cache backend api
backend_classes = {
'memcached': 'memcached.CacheClass',
'locmem': 'locmem.LocMemCache',
'file': 'filebased.FileBasedCache',
'db': 'db.DatabaseCache',
'dummy': 'dummy.DummyCache',
}
engine, host, params = parse_backend_uri(settings.CACHE_BACKEND)
if engine in backend_classes:
engine = 'django.core.cache.backends.%s' % backend_classes[engine]
else:
engine = '%s.CacheClass' % engine
defaults = {
'BACKEND': engine,
'LOCATION': host,
}
defaults.update(params)
settings.CACHES[DEFAULT_CACHE_ALIAS] = defaults
if DEFAULT_CACHE_ALIAS not in settings.CACHES:
raise ImproperlyConfigured("You must define a '%s' cache" % DEFAULT_CACHE_ALIAS)
def parse_backend_conf(backend, **kwargs):
"""
Helper function to parse the backend configuration
that doesn't use the URI notation.
"""
# Try to get the CACHES entry for the given backend name first
conf = settings.CACHES.get(backend, None)
if conf is not None:
args = conf.copy()
args.update(kwargs)
backend = args.pop('BACKEND')
location = args.pop('LOCATION', '')
return backend, location, args
else:
try:
# Trying to import the given backend, in case it's a dotted path
mod_path, cls_name = backend.rsplit('.', 1)
mod = importlib.import_module(mod_path)
backend_cls = getattr(mod, cls_name)
except (AttributeError, ImportError, ValueError):
raise InvalidCacheBackendError("Could not find backend '%s'" % backend)
location = kwargs.pop('LOCATION', '')
return backend, location, kwargs
raise InvalidCacheBackendError(
"Couldn't find a cache backend named '%s'" % backend)
def get_cache(backend, **kwargs):
"""
Function to load a cache backend dynamically. This is flexible by design
to allow different use cases:
To load a backend with the old URI-based notation::
cache = get_cache('locmem://')
To load a backend that is pre-defined in the settings::
cache = get_cache('default')
To load a backend with its dotted import path,
including arbitrary options::
cache = get_cache('django.core.cache.backends.memcached.MemcachedCache', **{
'LOCATION': '127.0.0.1:11211', 'TIMEOUT': 30,
})
"""
try:
if '://' in backend:
# for backwards compatibility
backend, location, params = parse_backend_uri(backend)
if backend in BACKENDS:
backend = 'django.core.cache.backends.%s' % BACKENDS[backend]
params.update(kwargs)
mod = importlib.import_module(backend)
backend_cls = mod.CacheClass
else:
backend, location, params = parse_backend_conf(backend, **kwargs)
mod_path, cls_name = backend.rsplit('.', 1)
mod = importlib.import_module(mod_path)
backend_cls = getattr(mod, cls_name)
except (AttributeError, ImportError), e:
raise InvalidCacheBackendError(
"Could not find backend '%s': %s" % (backend, e))
cache = backend_cls(location, params)
# Some caches -- python-memcached in particular -- need to do a cleanup at the
# end of a request cycle. If the cache provides a close() method, wire it up
# here.
if hasattr(cache, 'close'):
signals.request_finished.connect(cache.close)
return cache
cache = get_cache(DEFAULT_CACHE_ALIAS)
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