django1/django/core/cache/__init__.py

"""
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/cache.txt for information on the public API.
"""

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, 2.4.  Works on Python 2.6 but raises
        # PendingDeprecationWarning
        from cgi import parse_qsl

from django.conf import settings
from django.core import signals
from django.core.cache.backends.base import InvalidCacheBackendError, CacheKeyWarning
from django.utils import importlib

# 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',
}

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

def get_cache(backend_uri):
    scheme, host, params = parse_backend_uri(backend_uri)
    if scheme in BACKENDS:
        name = 'django.core.cache.backends.%s' % BACKENDS[scheme]
    else:
        name = scheme
    module = importlib.import_module(name)
    return module.CacheClass(host, params)

cache = get_cache(settings.CACHE_BACKEND)

# Some caches -- pythont-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)