How can you find unused functions in Python code?

In Python you can find unused code by using dynamic or static code analyzers. Two examples for dynamic analyzers are coverage and figleaf. They have the drawback that you have to run all possible branches of your code in order to find unused parts, but they also have the advantage that you get very reliable results.

Alternatively, you can use static code analyzers that just look at your code, but don't actually run it. They run much faster, but due to Python's dynamic nature the results may contain false positives. Two tools in this category are pyflakes and vulture. Pyflakes finds unused imports and unused local variables. Vulture finds all kinds of unused and unreachable code. (Full disclosure: I'm the maintainer of Vulture.)

The tools are available in the Python Package Index https://pypi.org/.

I'm not sure if this is helpful, but you might try using the coverage, figleaf or other similar modules, which record which parts of your source code is used as you actually run your scripts/application.

Because of the fairly strict way python code is presented, would it be that hard to build a list of functions based on a regex looking for def function_name(..) ?

And then search for each name and tot up how many times it features in the code. It wouldn't naturally take comments into account but as long as you're having a look at functions with less than two or three instances...

It's a bit Spartan but it sounds like a nice sleepy-weekend task =)