title: Count occurrences of an element in list
body: <p>I know that there are already a lot of questions about this specific topic, but I can't find a proper solution for my problem.</p>
  
  <p>I have the input: </p>
  
  <pre><code>2, 20, 15, 16, 17, 3, 8, 10, 7
  </code></pre>
  
  <p>I want to see if there are 'double' numbers in my code. I have tried working with this code. </p>
  
  <pre><code>lijst = input('Give a list:  ')
  teller = 0
  for i in lijst.split(','):
      if lijst.count(i) != 1:
          teller += 1
  print(teller != 0)
  </code></pre>
  
  <p>Normally I should get False, since there are no double numbers in the given list. However, I recieve True. I suggest that's because the 2 appears also in 20.</p>
  
  <pre><code>True
  </code></pre>
  
  <p>Does anyone know how to avoid this problem, so the the '2' isn't counted twice? </p>