How to use an integer variable as a parameter for a function?

Question

I'm trying to make a piece of code that will count up votes for three different candidates, and I'm using a function that uses the variable name (either A, B or C) as a parameter.

I'm trying to have it so that whenever a vote is counted for that candidate, it will call the function to increase the variable for that candidate by 1. However, with every way I've tried all 3 candidates will always have 0 votes counted, unless I completely remove the function.

I've tried several different ways of making the variables global variables but they all gave the same results.

A = 0
B = 0
C = 0

def after_vote(letter):
    letter = letter + 1
    print("Thank you for your vote.")

def winner(winner_letter, winner_votes):
    print("The winner was", winner_letter, "with", str(winner_votes), "votes.")

while True:
    vote = input("Please vote for either Candidate A, B or C. ").upper()
    if vote == "A":
        after_vote(A)
    elif vote == "B":
        after_vote(B)
    elif vote == "C":
        after_vote(C)
    elif vote == "END":
        print("Cadidate A got", str(A), "votes, Candidate B got", str(B), "votes, and Candidate C got", str(C), "votes.")
        if A > B and A > C:
            winner("A", A)
            break
        elif B > A and B > C:
            winner("B", B)
            break
        elif C > A and C > B:
            winner("C", C)
            break
        else:
            print("There was no clear winner.")
            break
    else:
        print("Please input a valid option.")

Answer 1

First of all, the idea is wrong. You don't want to handle global variables and pass names around. It could be done, but it is a bad idea.

A better option is to pass the variable to be modified to the function. However, the trick with integers is that they are immutable, so you cannot pass an integer to be modified by the function, as you would in C for instance.

What is left is either:

• pass a value to the function, return the modified value from the function; or
• pass a mutable object holding the value to the function

That was the theory, here is how to do it...

Solution 1: pass one value, return the modified value

def after_vote(value):
    print("Thank you for your vote.")
    # Instead of modifying value (impossible), return a different value
    return value + 1

A = after_vote(A)

Solution 2: pass a "mutable integer"

class MutableInteger:
    def __init__(value):
        self.value = value

A = MutableInteger(0)

def after_vote(count):
    # Integers cant be modified, but a _different_ integer can be put
    # into the "value" attribute of the mutable count object
    count.value += 1
    print("Thank you for your vote.")

after_vote(A)

Solution 3: pass a (mutable!) dictionary of all votes

votes = {'A': 0, 'B': 0, 'C': 0}

def after_vote(votes, choice):
    # Dictionaries are mutable, so you can update their values
    votes[choice] += 1
    print("Thank you for your vote.")

after_vote(votes, "A")

Solution 4 (the worst!): actually do what you asked for

def after_vote(letter):
    # Global variables are kept in a dictionary. globals() returns that dict
    # WARNING: I've never seen code which does this for a *good* reason
    globals()[letter] += 1
    print("Thank you for your vote.")