title: Time complexity of string concatenation in Python
body: <p>I'm analysing the complexity of my code.
  From what I found online, since strings are immutable in python, a concatenation of a string and a character should be O(len(string) + 1).</p>
  
  <p>Now, here is my piece of code (simplified):</p>
  
  <pre><code>word = ""
  for i in range(m):
      word = char_value + word
  return word
  </code></pre>
  
  <p>The total time complexity should be:</p>
  
  <p><em>(0+1) + (1+1) +...+ m = m(m+1)/2 = O(m^2)</em></p>
  
  <p>Is this correct?</p>