Getting started!

A comprehensive, fast, pure-Python memcached client library.

Basic Usage

from pymemcache.client.base import Client

client = Client(('localhost', 11211))
client.set('some_key', 'some_value')
result = client.get('some_key')

Using UNIX domain sockets

You can also connect to a local memcached server over a UNIX domain socket by passing the socket’s path to the client’s server parameter:

from pymemcache.client.base import Client

client = Client('/var/run/memcached/memcached.sock')

Using a memcached cluster

This will use a consistent hashing algorithm to choose which server to set/get the values from. It will also automatically rebalance depending on if a server goes down.

from pymemcache.client.hash import HashClient

client = HashClient([
    ('', 11211),
    ('', 11212)
client.set('some_key', 'some value')
result = client.get('some_key')


import json
from pymemcache.client.base import Client

def json_serializer(key, value):
    if type(value) == str:
        return value, 1
    return json.dumps(value), 2

def json_deserializer(key, value, flags):
   if flags == 1:
       return value
   if flags == 2:
       return json.loads(value)
   raise Exception("Unknown serialization format")

client = Client(('localhost', 11211), serializer=json_serializer,
client.set('key', {'a':'b', 'c':'d'})
result = client.get('key')

pymemcache provides a default pickle-based serializer:

from pymemcache.client.base import Client
from pymemcache import serde

class Foo(object):

client = Client(('localhost', 11211),
client.set('key', Foo())
result client.get('key')

The serializer uses the highest pickle protocol available. In order to make sure multiple versions of Python can read the protocol version, you can specify the version with pymemcache.serde.get_python_memcache_serializer().

client = Client(('localhost', 11211),

Deserialization with Python 3

def json_deserializer(key, value, flags):
    if flags == 1:
        return value.decode('utf-8')
    if flags == 2:
        return json.loads(value.decode('utf-8'))
    raise Exception("Unknown serialization format")

Key Constraints

This client implements the ASCII protocol of memcached. This means keys should not contain any of the following illegal characters:

Keys cannot have spaces, new lines, carriage returns, or null characters. We suggest that if you have unicode characters, or long keys, you use an effective hashing mechanism before calling this client.

At Pinterest, we have found that murmur3 hash is a great candidate for this. Alternatively you can set allow_unicode_keys to support unicode keys, but beware of what unicode encoding you use to make sure multiple clients can find the same key.

Best Practices

  • Always set the connect_timeout and timeout arguments in the pymemcache.client.base.Client constructor to avoid blocking your process when memcached is slow. You might also want to enable the no_delay option, which sets the TCP_NODELAY flag on the connection’s socket.
  • Use the noreply flag for a significant performance boost. The noreply flag is enabled by default for “set”, “add”, “replace”, “append”, “prepend”, and “delete”. It is disabled by default for “cas”, “incr” and “decr”. It obviously doesn’t apply to any get calls.
  • Use pymemcache.client.base.Client.get_many() and pymemcache.client.base.Client.gets_many() whenever possible, as they result in fewer round trip times for fetching multiple keys.
  • Use the ignore_exc flag to treat memcache/network errors as cache misses on calls to the get* methods. This prevents failures in memcache, or network errors, from killing your web requests. Do not use this flag if you need to know about errors from memcache, and make sure you have some other way to detect memcache server failures.


noreply will not read errors returned from the memcached server.

If a function with noreply=True causes an error on the server, it will still succeed and your next call which reads a response from memcached may fail unexpectedly.

pymemcached will try to catch and stop you from sending malformed inputs to memcached, but if you are having unexplained errors, setting noreply=False may help you troubleshoot the issue.