run_lambda is a Python package for running Python AWS Lambda functions locally. It offers a Python module for automated testing of Lambda functions, as well as a command-line interface for ad-hoc local invocations.

Doesn’t something like this already exist?

Not exactly. There are other programs for locally running Python Lambda functions. However, all of the other utilities (that I know of) only provide a command-line tool. A command-line tool is great for quick manual invocations. However, if you want to create robust, automated tests for your Lambda functions, a Python module that you can import and call is more appropriate. run_lambda is unique because it offers both a simple command-line tool for manual invocations, and an importable Python module for automated tests.


run_lambda supports

  • An interface for examining the result (return value, exception, timeout) of a function call
  • A full implementation of AWS Context objects
  • Function calls with or without a timeout
  • Resource usage profiling (memory and run-time)
  • Convenient mocking of objects and services inside Lambda functions


The easiest way to install is via pip:

$ pip install run_lambda

You can also download the source from Github.