Question

Simple example:

myList = [1, 2, 3, 4, 5]
for obj in myList:
  obj += 1
print myList

prints

[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]

while:

myList = [1, 2, 3, 4, 5]
for index in range(0,len(myList)):
  myList[index] += 1
print myList

prints

[1, 2, 3, 4, 5]
[2, 3, 4, 5, 6]

Conclusion:

1. Lists can be modified in place using global list access Lists can
2. List items can NOT be modified in place using the iterator object

All example code I can find uses the global list accessors to modify the list inplace.
Is it so evil to modify a list iterator?

Answer 1

in for obj in myList:, in every iteration, obj is a (shallow) copy of the element in myList. So the change on the obj does nothing to myList‘s elements.

It’s different with the Perl for my $obj (@myList) {}