title: Check python function determine isogram from codewars
body: <p>An isogram is a word that has no repeating letters, consecutive or non-consecutive. Implement a function that determines whether a string that contains only letters is an isogram. Assume the empty string is an isogram. Ignore letter case.</p>
  
  <pre><code>is_isogram("Dermatoglyphics" ) == true
  is_isogram("aba" ) == false
  is_isogram("moOse" ) == false # -- ignore letter case
  </code></pre>
  
  <p>Here is my code:</p>
  
  <pre><code>def is_isogram(string):
      string = string.lower()
      for char in string:
          if string.count(char) &gt; 1:
              return False
          else:
              return True
  </code></pre>
  
  <p>And when I tried to run the test code <code>Test.assert_equals(is_isogram("moOse"), False, "same chars may not be same case" )</code> It failed, but I thought I did convert everything into lowercase. Can someone help? </p>