Variable defined in a function is not usable in another function which calls the first

Question

I tried the following and got an error message that "x is not defined".

def test():
    x = 2
    y = 3
    return x

def main():
    test()
    print(2 + x)

main()

Why isn't it working?

`x` was assigned as a local variable in `test`, which means nothing to `main`. — NightShadeQueen, Jul 15 '15 at 18:07
There's a function called `locals()` that's real useful to looking around which local variables you have, and a matching function known as `globals()`. Don't actually use these in production code, but they're useful for "uh, what do I have in scope?" — NightShadeQueen, Jul 15 '15 at 18:08

score 3 · Answer 1 · answered Jul 15 '15 at 18:07

You need to assign x again, and the way to do that is say x = test(). The x from test only exists in x, which is why you need to reassign it.

It doesn't even have to be x, it could be y, or z: x is simply the name you return, the value you use in main() can be called anything!

Or, you can just call the function directly in main(), in which case you won't even need the first line in the main function:

def test():
    x = 2
    y = 3
    return x

def main():
    x = test() 
    print(2 + x) #or just `print(2 + test())`

main()

score 3 · Accepted Answer · edited May 23 '17 at 12:29

x is defined in test, but not in main

This means that x is not defined in main's scope

Take a look at this question for more details regarding scope. Specifically this answer.

If you want to use the value assigned to x in test, you need to assign the return value of test to a name:

def main():
    value_of_x_from_test = test() # This is the same as `x = 2` in `test`.
    print(2 + value_of_x_from_test)

score 1 · Answer 3 · answered Jul 15 '15 at 18:07

1

It's not working because of scope. X is defined in test, but not in main(). Try setting x = test() in main, and everything should work for you.

answered Jul 15 '15 at 18:07

Martin Lear

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juanmajmjr · Answer 4 · 2015-07-16T09:27:24.510

0

Because of x is defined locally in test(), it cannot be used by main. Instead you can use directly the output of test as it is shown in the following code:

def main():
    print(2 + test())

edited Jul 16 '15 at 09:27

answered Jul 15 '15 at 18:07

juanmajmjr

1,055
7
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Can you explain more your answer please ? – Zulu Jul 16 '15 at 00:05
@Zulu now is edited! – juanmajmjr Jul 16 '15 at 09:27

score 0 · Answer 5 · answered Jul 15 '15 at 18:07

0

In order to get the value of x in main(), you have to assign it to something:

def main():
    value = test() # The variable can be 'value' or any other valid name, including 'x'
    print(2 + value)

answered Jul 15 '15 at 18:07

Fernando Matsumoto

2,697
1
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Variable defined in a function is not usable in another function which calls the first

5 Answers5