Using for loop to amend a list of variables

Question

I've got the below code, with the aim to run through a list of defined variables and update them.

a = 1
b = 2
c = 3
test_list = [a, b, c]
print(test_list)

for i in test_list:
    i = 4

print(test_list)

When I run this though the test_list variables don't change. Any ideas what I'm doing wrong?

`test_list` is not, in any sense, a "list of defined variables". It's simply the list `[1, 2, 3]` - the variables that those values came from are no longer relevant. — jasonharper, Apr 06 '21 at 20:01
Lists don't contain *variables*. Lists contain *objects*. Variables *refer to objects*. `i = 4` just assigns an `int` object to the variable `i`, and won't affect any other variable you have. — juanpa.arrivillaga, Apr 06 '21 at 20:05

score 1 · Answer 1 · answered Apr 06 '21 at 19:56

Your for loop is returning you each element of the list, one at a time, in a variable called i. So, the first time through the loop, i is 1. You then change i to 4. That has nothing to do with the list.

It is possible to do what you ask:

for i in range(len(test_list)):
    test_list[i] = 4

but there are usually better ways to do that kind of thing. Tell us what you REALLY want and we can advise you.

Using for loop to amend a list of variables

1 Answers1