Do Python for loops work by reference?

Question

When using a for loop in Python to iterate over items in a list, will changing item (below) change the corresponding item in items?

Answer 1

Well, it really depends on the items.

Take the following case:

class test():
    pass

a = test()
a.value = 1

b = test()
b.value = 2

l = [a,b]

for item in l:
    item.value += 1

for item in l:
    print item.value

>>> 
2
3

and in this case:

l2 = [1,2,3]

for item in l2:
    item += 1

for item in l2:
    print item

>>> 
1
2
3

So as you can see, you need to understand the pointers as Martijn said.