title: count upper and lowercase letters in python using recursion
body: <p>I need help coming up with this python function.
  A recursive function count_upper_lower() that takes a non-empty string as its argument and returns a tuple containing the counts of how many letters in the string are uppercase and how many are lowercase (in that order).
  For instance </p>
  
  <pre><code>print (count_upper_lower(’Town Hall University’)) 
  </code></pre>
  
  <p>would return</p>
  
  <pre><code>(3, 15)
  </code></pre>
  
  <p>this is what i have so far</p>
  
  <pre><code>def count_upper_lower(word):
      upper = 0
      lower = 0
      if word == "":
          upper = 0
          lower = 0
          return upper, lower
      elif word[0].isupper():
          upper = 1 + count_upper_lower(word[1:])
          return upper , lower
  
  
      elif word[0].islower():
          lower = 1 + count_upper_lower(word[1:])
          return upper , lower
  
      else:
          upper = 0 + count_upper_lower(word[1:])
          lower = 0 + count_upper_lower(word[1:])
          return upper, lower
  </code></pre>
  
  <p>i am getting the following error:</p>
  
  <pre><code>TypeError: unsupported operand type(s) for +: 'int' and 'tuple'
  </code></pre>