Is there any implementation of Friendly Enough Expression Language or any sub-parts of Decision Modeling Notation (DMN) defined by Object Modeling Group (OMG)?
Yes - pyDMNrules in an implementation of DMN in Python. It's available from PyPi.
You can install it with the command
pip install pyDMNrules. This will also install pySFeel - a dependency and an implementation of S-FEEL (with a fair bit of FEEL thrown in for good measure - just no support for user defined functions).
Disclaimer: I am the author of pyDMNrules and pySFeel.