for i in range(len(secretWord)):
        if secretWord[i] in correctLetters:
            blanks = blanks[:i] + secretWord[i] + blanks[i+1]

for i in range(len(secretWord)):
    if secretWord[i] in correctLetters:
        # blanks = the underscores from 0 to i found in blanks
        # + the secret letter at index i in secretWord
        # + the underscores from i+1 to the end found in blanks
        blanks = blanks[:i] + secretWord[i] + blanks[i+1:]

blanks = _____ (5 underscores)
secretWord = Hi

lets assume that 'i' is in correct letters and 'h' is not
(loop 2 times since len('hi') == 2)
------------------------------------------------------
First iteration:

if 'h' in correctLetters (its not so skip):
------------------------------------------------------
Second iteration:

'i' is in correctLetters

blanks = __ (underscores from 0 to 1 in blanks)
   + 'i' (the letter at secretWord[1])
   + __ (blanks[2:onward] - the rest of the underscores ignoring the one where the letter goes)

for i in range(len(secretWord)):
# i is index of secretword
  if secretWord[i] in correctLetters:
  # checking if letter secretWord[i] is in correctletters
  # if it is in, replace _ in blacks  to secretWord[i]
  # recreate blank list by using everything before index i, secretWord[i], and everything after index i
    blanks = blanks[:i] + secretWord[i] + blanks[i+1]