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"Base Cache class."
import warnings
from django.core.exceptions import ImproperlyConfigured, DjangoRuntimeWarning
from django.utils.encoding import smart_str
from django.utils.importlib import import_module
class InvalidCacheBackendError(ImproperlyConfigured):
pass
class CacheKeyWarning(DjangoRuntimeWarning):
pass
# Memcached does not accept keys longer than this.
MEMCACHE_MAX_KEY_LENGTH = 250
def default_key_func(key, key_prefix, version):
"""
Default function to generate keys.
Constructs the key used by all other methods. By default it prepends
the `key_prefix'. KEY_FUNCTION can be used to specify an alternate
function with custom key making behavior.
"""
return ':'.join([key_prefix, str(version), smart_str(key)])
def get_key_func(key_func):
"""
Function to decide which key function to use.
Defaults to ``default_key_func``.
"""
if key_func is not None:
if callable(key_func):
return key_func
else:
key_func_module_path, key_func_name = key_func.rsplit('.', 1)
key_func_module = import_module(key_func_module_path)
return getattr(key_func_module, key_func_name)
return default_key_func
class BaseCache(object):
def __init__(self, params):
timeout = params.get('timeout', params.get('TIMEOUT', 300))
try:
timeout = int(timeout)
except (ValueError, TypeError):
timeout = 300
self.default_timeout = timeout
options = params.get('OPTIONS', {})
max_entries = params.get('max_entries', options.get('MAX_ENTRIES', 300))
try:
self._max_entries = int(max_entries)
except (ValueError, TypeError):
self._max_entries = 300
cull_frequency = params.get('cull_frequency', options.get('CULL_FREQUENCY', 3))
try:
self._cull_frequency = int(cull_frequency)
except (ValueError, TypeError):
self._cull_frequency = 3
self.key_prefix = smart_str(params.get('KEY_PREFIX', ''))
self.version = params.get('VERSION', 1)
self.key_func = get_key_func(params.get('KEY_FUNCTION', None))
def make_key(self, key, version=None):
"""Constructs the key used by all other methods. By default it
uses the key_func to generate a key (which, by default,
prepends the `key_prefix' and 'version'). An different key
function can be provided at the time of cache construction;
alternatively, you can subclass the cache backend to provide
custom key making behavior.
"""
if version is None:
version = self.version
new_key = self.key_func(key, self.key_prefix, version)
return new_key
def add(self, key, value, timeout=None, version=None):
"""
Set a value in the cache if the key does not already exist. If
timeout is given, that timeout will be used for the key; otherwise
the default cache timeout will be used.
Returns True if the value was stored, False otherwise.
"""
raise NotImplementedError
def get(self, key, default=None, version=None):
"""
Fetch a given key from the cache. If the key does not exist, return
default, which itself defaults to None.
"""
raise NotImplementedError
def set(self, key, value, timeout=None, version=None):
"""
Set a value in the cache. If timeout is given, that timeout will be
used for the key; otherwise the default cache timeout will be used.
"""
raise NotImplementedError
def delete(self, key, version=None):
"""
Delete a key from the cache, failing silently.
"""
raise NotImplementedError
def get_many(self, keys, version=None):
"""
Fetch a bunch of keys from the cache. For certain backends (memcached,
pgsql) this can be *much* faster when fetching multiple values.
Returns a dict mapping each key in keys to its value. If the given
key is missing, it will be missing from the response dict.
"""
d = {}
for k in keys:
val = self.get(k, version=version)
if val is not None:
d[k] = val
return d
def has_key(self, key, version=None):
"""
Returns True if the key is in the cache and has not expired.
"""
return self.get(key, version=version) is not None
def incr(self, key, delta=1, version=None):
"""
Add delta to value in the cache. If the key does not exist, raise a
ValueError exception.
"""
value = self.get(key, version=version)
if value is None:
raise ValueError("Key '%s' not found" % key)
new_value = value + delta
self.set(key, new_value, version=version)
return new_value
def decr(self, key, delta=1, version=None):
"""
Subtract delta from value in the cache. If the key does not exist, raise
a ValueError exception.
"""
return self.incr(key, -delta, version=version)
def __contains__(self, key):
"""
Returns True if the key is in the cache and has not expired.
"""
# This is a separate method, rather than just a copy of has_key(),
# so that it always has the same functionality as has_key(), even
# if a subclass overrides it.
return self.has_key(key)
def set_many(self, data, timeout=None, version=None):
"""
Set a bunch of values in the cache at once from a dict of key/value
pairs. For certain backends (memcached), this is much more efficient
than calling set() multiple times.
If timeout is given, that timeout will be used for the key; otherwise
the default cache timeout will be used.
"""
for key, value in data.items():
self.set(key, value, timeout=timeout, version=version)
def delete_many(self, keys, version=None):
"""
Set a bunch of values in the cache at once. For certain backends
(memcached), this is much more efficient than calling delete() multiple
times.
"""
for key in keys:
self.delete(key, version=version)
def clear(self):
"""Remove *all* values from the cache at once."""
raise NotImplementedError
def validate_key(self, key):
"""
Warn about keys that would not be portable to the memcached
backend. This encourages (but does not force) writing backend-portable
cache code.
"""
if len(key) > MEMCACHE_MAX_KEY_LENGTH:
warnings.warn('Cache key will cause errors if used with memcached: '
'%s (longer than %s)' % (key, MEMCACHE_MAX_KEY_LENGTH),
CacheKeyWarning)
for char in key:
if ord(char) < 33 or ord(char) == 127:
warnings.warn('Cache key contains characters that will cause '
'errors if used with memcached: %r' % key,
CacheKeyWarning)
def incr_version(self, key, delta=1, version=None):
"""Adds delta to the cache version for the supplied key. Returns the
new version.
"""
if version is None:
version = self.version
value = self.get(key, version=version)
if value is None:
raise ValueError("Key '%s' not found" % key)
self.set(key, value, version=version+delta)
self.delete(key, version=version)
return version+delta
def decr_version(self, key, delta=1, version=None):
"""Substracts delta from the cache version for the supplied key. Returns
the new version.
"""
return self.incr_version(key, -delta, version)
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