make the longest palindrome in a string with a single "_"

make_maxpalindrome.py

def make_longest_palindrome(s):
  '''
  From a string object with a single "_", return the length of the longest possible palindrome and the letter to insert in place of "_"
  '''
  l = list(s)
  print(l)
  maxlen = 0
  blank = "_"
  blank_temp = "_"
  # check all possible ordered subsets of the list for palindrome ticker
  for lefti in range(len(l)-1):
    for righti in range(lefti + 1, len(l)):
      pal_count = 0
      if righti - lefti == 1:
        if l[lefti] == l[righti] or "_" in (l[lefti], l[righti]):
          pal_count += 2
          if l[righti] == "_":
            blank_temp = l[lefti]
          elif l[lefti] == "_":
            blank_temp = l[righti]
      else:
        if (righti - lefti + 1)%2 != 0:
          pal_count += 1
          if l[lefti + int((righti - lefti)/2)] == "_":
            blank_temp = "any"
        for step in range(int((righti - lefti + 1)/2)):
          if l[lefti + step] == l[righti - step] or l[lefti + step] == "_" or l[righti - step] == "_":
            pal_count += 2
            if l[righti - step] == "_":
              blank_temp = l[lefti + step]
            elif l[lefti + step] == "_":
              blank_temp = l[righti - step]
          else:
            break        
      if pal_count > maxlen:
        maxlen = pal_count
        blank = blank_temp
  return 'The longest palindrome is ' + str(maxlen) + ' characters with "_" set to: ' + blank

if __name__ == "__main__":
  valid_s = False
  while not valid_s:
    s = input('Word or phrase with one "_" to create longest palindrome: ')
    l = list(s)
    if l.count("_") < 2:
      valid_s = True 
  print(make_longest_palindrome(s))