title: .upper not working in python
body: <p>I currently have this code</p>
  
  <pre><code>num_lines = int(input())
  lines = []
  tempy = ''
  ctr = 1
  abc = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'
  }
  for i in range(0, num_lines):
    tempy = input()
    lines.append([])
    lines[i].append(tempy)
  
  
  for o in range(0, num_lines):
    for p  in range(0, len(lines[o])):
      for u in range(0, len(lines[o][p])):
        if lines[o][p][u] in abc:
          lines = str(lines)
          if ctr % 2 == 0:
            print(lines[o][p][u])
            lines[o][p][u].upper()
          else:
            print(lines[o][p][u])
            lines[o][p][u].lower()
          ctr += 1
  
  print(lines)
  </code></pre>
  
  <p>but the .upper line does not seem to have effect, can anyone please tell me why?</p>
  
  <p>Thank you in advance, and if there is an answer already please kindly tell me that instead of marking as a duplicate cause I did search for a good hour</p>