from itertools import zip_longest

chars = []
correct = 'hangman'
guess = 'winger'
for c, g in zip_longest(correct, guess, fillvalue='_'):
    if c == g:
        chars.append(c)
    else:
        chars.append('_')

print(chars)
# ['_', '_', 'n', 'g', '_', '_', '_']

word = ''.join(chars)
print(word)
# __ng___