title: Peek stack in python 3
body: <p>Question: Implement peek(stack) that returns, but doesn't remove, the top element from a stack. Return None if list is empty. </p>
  
  <p>I tried many times but did not successfully get it, anyone can help? </p>
  
  <p>My attempt:</p>
  
  <pre><code>def peek_stack(stack):
      if stack == []:
          return None
      else:
          s= stack.copy()
          return s.pop(0)
  </code></pre>