zip functionality in python behaving weird

Question

>>> l1 = ['A', 'B', 'C']
>>> l2 = ['G', 'F', 'K', 'J']
>>> for (i, j) in zip(l1, l2):
      print(i, j)
      l1.pop(0)
      print(l1)
      print(l2)

output is : 'A' A G ['B', 'C'] ['G', 'F', 'K', 'J'] 'B' C F ['C'] ['G', 'F', 'K', 'J']

Expected : 'A' A G # line 2 ['B', 'C'] ['G', 'F', 'K', 'J'] 'B'
C F # line 3 ['C'] ['G', 'F', 'K', 'J']

l2 still has ['C']. Why ? Also, at line 2 how come A is there, when A is already popped. If it means, that i took the value already before popping, then why line 3 has C F. It should be B F.

Please explain. I am totally confused here.

Answer 1

I don't see a problem because you are popping A after the zip function is executed. So even if you remove all elements in l1 and l2 in the first iteration, the loop executes the same because the zip() function had already returned the values before first iteration. range(), zip() or whatever function you provide on the for in , it will execute first, then it will iterate, modifying the original values won't change anything, because it is already returned as a separate value.