A Python dictionary implementation designed to act as an in-memory cache for FaaS environments.

Formally you would describe this a memory constrained LRU TTL cache dict.

This is implementation only uses core Python stdlib with no external dependencies.


This was originally designed to be used as an in-memory cache for AWS Lambda.

In most FaaS environments, successive quick calls of the function persists variables in the global scope. We can leverage this to cache data for future calls.

FaaS runtimes have limited RAM capacities so this library allows you to set a max mebibyte size for the dict. It also allows setting an optional max items length.

Items are kept in order with the LRU at the HEAD of the list.

Items are deleted if they expire, or from the head (LRU) if the cache is out of space.



  • Performance degrades with size, you will need to test this for your use case. Though in most circumstances this will be much faster than performing a network call to a cache.
  • The library should be thread-safe, but limited testing has gone into this.


CPython 3.7 or greater. No extra dependencies are required.


This code is distributed under an open license. Feel free to fork it or preferably open a PR.


Thanks to mobilityhouse/ttldict for their implementation which served as a starting point.


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