Memcached Backend¶
- class cachelib.memcached.MemcachedCache(servers=None, default_timeout=300, key_prefix=None)¶
Bases:
BaseCache
A cache that uses memcached as backend.
The first argument can either be an object that resembles the API of a
memcache.Client
or a tuple/list of server addresses. In the event that a tuple/list is passed, Werkzeug tries to import the best available memcache library.This cache looks into the following packages/modules to find bindings for memcached:
pylibmc
google.appengine.api.memcached
memcached
libmc
Implementation notes: This cache backend works around some limitations in memcached to simplify the interface. For example unicode keys are encoded to utf-8 on the fly. Methods such as
get_dict()
return the keys in the same format as passed. Furthermore all get methods silently ignore key errors to not cause problems when untrusted user data is passed to the get methods which is often the case in web applications.- Parameters:
servers (Any) – a list or tuple of server addresses or alternatively a
memcache.Client
or a compatible client.default_timeout (int) – the default timeout that is used if no timeout is specified on
set()
. A timeout of 0 indicates that the cache never expires.key_prefix (str | None) – a prefix that is added before all keys. This makes it possible to use the same memcached server for different applications. Keep in mind that
clear()
will also clear keys with a different prefix.
- add(key, value, timeout=None)¶
Works like
set()
but does not overwrite the values of already existing keys.- Parameters:
key (str) – the key to set
value (Any) – the value for the key
timeout (int | None) – the cache timeout for the key in seconds (if not specified, it uses the default timeout). A timeout of 0 indicates that the cache never expires.
- Returns:
Same as
set()
, but alsoFalse
for already existing keys.- Return type:
boolean
- clear()¶
Clears the cache. Keep in mind that not all caches support completely clearing the cache.
- Returns:
Whether the cache has been cleared.
- Return type:
boolean
- dec(key, delta=1)¶
Decrements the value of a key by delta. If the key does not yet exist it is initialized with -delta.
For supporting caches this is an atomic operation.
- Parameters:
key (str) – the key to increment.
delta (int) – the delta to subtract.
- Returns:
The new value or None for backend errors.
- Return type:
int | None
- delete(key)¶
Delete key from the cache.
- Parameters:
key (str) – the key to delete.
- Returns:
Whether the key existed and has been deleted.
- Return type:
boolean
- delete_many(*keys)¶
Deletes multiple keys at once.
- Parameters:
keys (str) – The function accepts multiple keys as positional arguments.
- Returns:
A list containing all successfully deleted keys
- Return type:
boolean
- get(key)¶
Look up key in the cache and return the value for it.
- Parameters:
key (str) – the key to be looked up.
- Returns:
The value if it exists and is readable, else
None
.- Return type:
Any
- get_dict(*keys)¶
Like
get_many()
but return a dict:d = cache.get_dict("foo", "bar") foo = d["foo"] bar = d["bar"]
- Parameters:
keys (str) – The function accepts multiple keys as positional arguments.
- Return type:
Dict[str, Any]
- get_many(*keys)¶
Returns a list of values for the given keys. For each key an item in the list is created:
foo, bar = cache.get_many("foo", "bar")
Has the same error handling as
get()
.- Parameters:
keys (str) – The function accepts multiple keys as positional arguments.
- Return type:
List[Any]
- has(key)¶
Checks if a key exists in the cache without returning it. This is a cheap operation that bypasses loading the actual data on the backend.
- Parameters:
key (str) – the key to check
- Return type:
bool
- import_preferred_memcache_lib(servers)¶
Returns an initialized memcache client. Used by the constructor.
- Parameters:
servers (Any) –
- Return type:
Any
- inc(key, delta=1)¶
Increments the value of a key by delta. If the key does not yet exist it is initialized with delta.
For supporting caches this is an atomic operation.
- Parameters:
key (str) – the key to increment.
delta (int) – the delta to add.
- Returns:
The new value or
None
for backend errors.- Return type:
int | None
- set(key, value, timeout=None)¶
Add a new key/value to the cache (overwrites value, if key already exists in the cache).
- Parameters:
key (str) – the key to set
value (Any) – the value for the key
timeout (int | None) – the cache timeout for the key in seconds (if not specified, it uses the default timeout). A timeout of 0 indicates that the cache never expires.
- Returns:
True
if key has been updated,False
for backend errors. Pickling errors, however, will raise a subclass ofpickle.PickleError
.- Return type:
boolean
- set_many(mapping, timeout=None)¶
Sets multiple keys and values from a mapping.
- Parameters:
mapping (Dict[str, Any]) – a mapping with the keys/values to set.
timeout (int | None) – the cache timeout for the key in seconds (if not specified, it uses the default timeout). A timeout of 0 indicates that the cache never expires.
- Returns:
A list containing all keys successfully set
- Return type:
boolean