Question

I sometimes forget to return result from a function:

def f(*args):
  # do stuff
  result = # an expression
  # oops forgot to return result

Since None is a valid value in my application, this does not raise any exception or even any alarm in the caller. Of course, I’m trying to be careful. But I was wondering if there’s some neat approach to warn me about any function that doesn’t explicitly return a value.

Perhaps a regex I can run through my code to find such cases. Or some code checking tool (hopefully available under the Windows environment).

I was even thinking using a decorator like this:

def requires_return(func):
  def new_func(*args, **kwargs):
    result = func(*args, **kwargs)
    if result is None:
      print('Warning: {} may be missing a return statement'.format(func.__name__))
    return result

But this wouldn’t work because:

1. Many false alarms: each time a function actually returns None. I can’t stop using None in my application without creating really ugly code elsewhere.

2. In any case, adding a decorator to every function seems super-ugly.

Note that I do have functions where I intentionally don’t have a return statement. I tend to maintain a certain naming convention, which allows me easily to distinguish them. (Specifically, every function that starts with get_ must have a return statement.)

Answer 1

Pylint will sometimes catch this kind of error. In particular if you assign to result but then never use it:

pylint zorg.py
************* Module zorg
W0612:  5:zorg: Unused variable 'result'

However, it does not catch the case where you build up result in pieces and then forget to return it (because then the variable is not “unused”).

Depending on many other things, though, pylint, through its static type-analysis, may catch the failure to return a value.