How to find unused code in Python web site?

As other answers indicate coverage.py accurately finds out which parts of the code are never executed, but coverage requires your code to be actually run to perform the analysis. Vulture on the other hand, runs static analysis for finding dead (unused code) for Python Programs. Also, if you run vulture on both your library and test suite, you might be able to find untested code.

Vulture is a standard PyPI package and can be installed using pip:

$ pip install vulture

Run vulture using the command:

$ vulture apps/ tests/ --exclude settings

Bear in mind that due to Python's dynamic nature, there may be some false positives, but they can be dealt with by the means of "Whitelists" - Please refer to this answer by Rahul for more information on how to use Vulture with django and tackle false positives.

It depends on what you mean by unused code.

For unreachable dead code, like functions are were never called, classes that are never instantiated, you can use a pure static code analyzer to find them. Pylint is a good option. Bear in mind that this is not 100% accurate, false positive is possible:

# static analysis can't detect methods called this way
func = getattr(obj, "func_name")
func() 

For code that are reachable, but never reached. You have to rely on tools like coverage.py, and improve your test coverage.

On a well tested project, coverage would be ideal but with some untested legacy code I don't think there is a magical tool.

You could write a big test loading all the pages and run coverage to get some indication.

Cowboy style:

If it's not some critical code and you're fairly sure it's unused (i.e. not handling payments, etc.). Comment it out, check that the tests pass, deploy and wait a week or so before removing it definitely (or putting it back if you got a notification).