Dictionary value not updating as expected when using -=

Question

I have a dictionary and a word:

check = {'a': 3, 'e': 1, 'p': 2, 'r': 1, 'u': 1, 't': 1}
word = 'rapturerererer'

I'm looking to run a test if all the letters from word are in check. So I need to keep a running count of all the used up letters and check if there are any negatives at the end.

I have code but it always caps out the values at 0 and never returns the negative values:

for letter in word:
    if check.get(letter):
        check[letter] -= 1
print(check)

{'a': 2, 'p': 1, 'r': 0, 'e': 0, 't': 0, 'u': 0}

What I'm expecting is this:

{'a': 2, 'p': 1, 'r': -5, 'e': -4, 't': 0, 'u': 0}

Can anyone explain why it's stopping at 0 for these values?

Answer 1

if check.get(letter):
    check[letter] -= 1

if check.get(letter) doesn't only fail if letter is missing; it also fails if the value in the dict is "falsy". None is falsy, and so is 0. Once it hits 0 the test fails and no more decrementing happens.

Use in instead.

if letter in check:
    check[letter] -= 1