Nose of Yeti

This is a project creates a custom Python codec that lets the developer write their tests using an RSpec inspired DSL (i.e. describe and it blocks).

It uses the fact that python allows the registration of a codec that can be used to read in source code and modify it at import time.

NoseOfYeti uses this technique to find files with a particular coding declaration on the first line of a file to turn the rspec inspired DSL into ordinary python that is then executed as if it were written like that in the first place.

The original idea comes from @fmeyer who wrote this blog post and a simple proof of concept before it was picked up and worked on by @hltbra in this repo.

@delfick discovered this work in 2010 and over the following decade plus has improved on the concept, giving it more features and integration with python tooling.

The documentation can be found at and the code over at

Updating nose-of-yeti version

It is recommended any .pyc files are removed when NoseOfYeti is upgraded.

The Python interpreter skips the translation process if it sees a .pyc file (unless the .py file has changed since the .pyc file was created). This means that any changes in the translation process won’t apply until either the .pyc files are removed or all the .py files have been changed.