How to use local variable in a function and return it?

Question

I am trying to create a script that sets a local variable, references it from a function, and can return the manipulated value back to the main scope (or whatever it\'s call

Answer 1

One approach is to use mutable values, like dicts or lists:

settings = dict(
    chambersinreactor = 0,
    cardsdiscarded = 0
)

def find_chamber_discard():
    settings['chambersinreactor'] += 1
    settings['cardsdiscarded'] += 1

find_chamber_discard()

print settings['chambersinreactor']
print settings['cardsdiscarded']

However, if you have a function that is changing some state, you're probably better off wrapping that all up in class, as that's what they're for:

class CardCounter(object):
    def __init__(self):
        chambersinreactor = 0
        cardsdiscarded = 0

    def find_chamber_discard(self, hand):
        for card in hand:
            if card.is_chamber:
                self.chambersinreactor += 1
            if card.is_discarded:
                self.cardsdiscarded += 1

If what you're doing is counting, maybe you could use Counter:

from collections import Counter

def test_for_chamberness(x): return x == 'C'
def test_for_discarded(x): return x == 'D'

def chamber_or_discard(card):
    if test_for_chamberness(card):
        return 'chambersinreactor'
    if test_for_discarded(card):
        return 'cardsdiscarded'

hand = ['C','C','D','X','D','E','C']

print Counter(
    x for x in (chamber_or_discard(card) for card in hand) if x is not None
)

Personally, I'd go for the class approach, perhaps even wrapping Counter, as it keeps all the associated functionality together.