Live-reloading of Python Modules in the Python REPL / IPython / Jupyter Console

Often, I would work on a Python module and add changes to it live, which I would then want to test immediately. Piece of cake! Add the changes and execute the script again. Well, that’s certainly a way, but as modules get bigger, they tend to import other modules, or do some preliminary setup work.

With time, I have developed this practice of opening up a Python REPL (though I recommend IPython or the Jupyter Console for that), importing my in-progress module and singling out separate functions I would like to test. The problem is, when I do changes to the Python code (like, add a new function), they are not immediately usable, because neither the Python REPL, nor IPython / Jupyter would auto-reload them.

Give me the code

Yes, we are coming to that

General Way

Python 3 supports inline reloading of modules using a function called, well clever enough, reload. It used to be a built-in function in Python 2, but this is no longer the case. If you are using Python 3.2+, you should import it extra:

For Python 3.2 and 3.3:

import importlib
importlib.reload(some_module)

For Python 3.4+:

import imp
imp.reload(some_module)

IPython/Jupyter Magic

Jupyter comes with a set of extensions only applicable to the Jupyter/iPython sessions, called magics. One of these “magics” is the ability to load custom extensions, one of which allows auto-reloading of modules. To enable this, you should add the following two commands, before any imports:

%load_ext autoreload
%autoreload 2
# you can check out the the documentation for the rest of the autoreaload modes
# by apending a question mark to %autoreload, like this:
# %autoreload?

This way, as soon as you hit Save in your code editor, you should be able to re-run a Jupyter cell or an iPython line again, and if it is calling your module, it should automatically call the latest version.

Links

Jupyter / IPython: After editing a module, changes are not effective without kernel restart – Enthought Knowledge Base
python - Reloading submodules in IPython - Stack Overflow

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NOTE: This post first appeared on my blog