title: The difference between "for item in list L" and "for item in list L[:]"
body: <p>What causes the difference of these two lists?</p>
  
  <p><a href="https://i.stack.imgur.com/pN1Qb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pN1Qb.png" alt="enter image description here"></a>
  <a href="https://i.stack.imgur.com/zZaZU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zZaZU.png" alt="enter image description here"></a></p>