While loop goes on forever despite condition being met

import random
word_list = ["aardvark", "baboon", "camel"]
chosen_word = random.choice(word_list)
word_length = len(chosen_word)
display = []

print(f'Pssst, the solution is {chosen_word}.')

display = []
for _ in range(word_length):
    display += "_"


guess = input("Guess a letter: ").lower()

def check_letter(display):
  for position in range(word_length):
      letter = chosen_word[position]
      if letter == guess:
          display[position] = letter
  print(display)

check_letter(display)

for item in display:
  while item == "_":
    guess = input("Guess a letter: ").lower()
    check_letter(display)
    if (''.join([str(elem) for elem in display]) == chosen_word) :
        break


print("You've Won")

I played with your code for much longer than I thought I would. The problem is subtle.

The issue with your code is that item never changes it’s value (despite the for loop). And that’s why the problem is subtle – the for loop (for item in display:) only iterates once because the while loop it contains is endless. The while loop is endless is because nothing in the while loop changes the value of item.

All that said, I can see why you are asking here at SO. Here’s a bit of code that eliminates the for loop for just a while loop. I’ve eliminated the item variable – it doesn’t change anyway. Rather, the condition that keeps us in the loop is there is still an underscore in the display variable.

import random
word_list = ["aardvark", "baboon", "camel"]
chosen_word = random.choice(word_list)
word_length = len(chosen_word)


print(f'Pssst, the solution is {chosen_word}.')

display = []
for _ in range(word_length):
    display += "_"


guess = input("Guess a letter: ").lower()

def check_letter():
  for position in range(word_length):
      letter = chosen_word[position]
      if letter == guess:
          display[position] = letter
  print(display)

check_letter()

while '_' in display:
    guess = input("Guess a letter: ").lower()
    check_letter()

print("You've Won")

Here is an alternate solution. I also added a check to see if the user has already entered a given letter and output to say that letter has already been guessed.

from calendar import c
import random
word_list = ["aardvark", "baboon", "camel"]
chosen_word = random.choice(word_list)
word_length = len(chosen_word)
guessed_word = []


print(f'Pssst, the solution is {chosen_word}.')

display = []
for _ in range(word_length):
    display += "_"


guess = input("Guess a letter: ").lower()

def check_letter():
  for position in range(word_length):
      letter = chosen_word[position]
      if letter == guess:
          display[position] = letter
          # append the letter to the guessed_word list at the correct position
          guessed_word.insert(position, letter)
  print(display)

check_letter()

for item in display:
    
    while item == "_":
        gw = ''.join(guessed_word)
        cw = ''.join(chosen_word)
        if gw == cw:
            print("You win")
            break
        else:    
            guess = input("Guess a letter: ").lower()
            if guess in display:
                print(f"You've already guessed {guess}")
            else:
                check_letter()