Change variable value for each variable in list

Question

Suppose we have a list variables with the variables [a, b, c]. The code shall check if the variable value is a of type string with the text "None". The variable value shall be updated to "" if true. Using a for loop, I would write:

a = 1
b = 2
c = 3
variables = [a, b, c]

for i in range(len(variables)):
    variables[i] = 55

print(variables)
print(a, b, c)

This outputs:

[55, 55, 55]
1 2 3

Why don't the variables update their value?

You don't have a list of variables. You have a list of values. Read nedbatchelder.com/text/names.html. — chepner
– chepner, Commented Mar 25, 2019 at 16:19
You need to update the list itself, not a single item of the list. — 9769953
– 9769953, Commented Mar 25, 2019 at 16:21
Related (the opposite problem, basically): How to update a list of variables in python? — Aran-Fey
– Aran-Fey, Commented Mar 25, 2019 at 16:29
@deceze Those duplicates certainly solve the OP's problem, but they do nothing to explain why the OP's code doesn't work. The OP specifically asked why the code doesn't work. I think this should be reopened. (I tried to find a better duplicate, but couldn't.) — Aran-Fey
– Aran-Fey, Commented Mar 25, 2019 at 16:31

chepner · Accepted Answer · 2019-03-25 16:20:19Z

3

All you are doing is overwriting the value of the local variable variable, not an element in variables. You'll need to iterate over the indices and assign to variables[i] directly:

for i, value in enumerate(variables):
    if value == "None":
        variables[i] = ""

answered Mar 25, 2019 at 16:20

chepner

538k77 gold badges594 silver badges746 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

FredMaster · Accepted Answer · 2019-03-25 16:25:52Z

0

If I reproduce your example the variable "variable" will indeed update. However, the list of variables "variables" will not. Because you are not telling it to change.

There are several ways to change this. If this is a small list I would simply create a new list

variables = [1,2,3,4,"None",5,1,"foo","bar"]

new_variables = [0 if variable == "None" else variable for variable in variables]

Hope this helps!

answered Mar 25, 2019 at 16:25

FredMaster

1,4993 gold badges20 silver badges39 bronze badges

Collectives™ on Stack Overflow

Change variable value for each variable in list

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related