Factored out loop control in Python

Question

I have a for loop in python like this:

for item in items:
    onwards = make_flow_decision(item)
    if onwards == 'break':
        break
    elif onwards == 'continue':
        continue
    elif onwards == 'carry_on':
        process_the_item(item)

So idea is that flow control for the loop is factored out because it is really complex.

Is there a better way of doing this than passing strings around and checking for special strings like 'continue', 'break', and 'carry_on'?

Looking for ideas generally that make this a little more elegant.

Answer 1

What you could do, is factor out the filtering and breaking into a generator, which can be really handy if that logic is used multiple times, with different processing in the middle.

def relevant_items(items):
    for item in items:
        # logic to continue or break/return goes here
        yield item

def process_many_items(items):
    for item in relevant_items(items):
        process_item(item)

This does however add an extra layer of indirection, which is probably only worth it if the relevant_items method would make sense outside process_many_items.

Answer 2

You can use enumerated types instead of strings, and keep your implementation.

Or, if you don't mind using exceptions you can write:

try:
    for item in items:
        if shall_process(item):
            process_the_item(item)
except StopIteration:
    pass

Here, shall_process returns a boolean and can throw an exception to exit the iteration.