title: My for loop and while loop stops at specific number
body: <p>I would like to write a program that excludes every string from a list.</p>
  
  <pre><code>lst =  ["a", "e", "i", "o", "u"]
  for i in lst:
   if isinstance(i, str):
     lst.remove(i)
  print(lst)
  </code></pre>
  
  <p>I would like to know why the result of the above code is<code>['e', 'o']</code>.</p>