How to make variable accessible inside another function

Question

Consider this example:

def func1():
    val = 1
    res = [1]
    def fun2():
        print(res)
        print(val)
        val = 2 
    fun2()
    print(val)

func1()

It raises the following exception:

UnboundLocalError: local variable 'val' referenced before assignment

List res can be accessed by fun2, but val cannot. I know list is mutable and int is not, but is there a way to make val accessible by fun2 as well? In a class, I could easily achieve that with self.val, but is there a way to do it inside a function?

It's because the `val = 2` makes a new (local to fun2) variable called `val`. Remove that line and it works. — Blorgbeard, Jun 14 '19 at 21:38
https://stackoverflow.com/questions/4851463/in-python-2-how-do-i-write-to-variable-in-the-parent-scope — Blorgbeard, Jun 14 '19 at 21:39
Or if this is python 3, you can add `nonlocal val` to the top of `fun2` definition. — Blorgbeard, Jun 14 '19 at 21:42
Mutability is irrelevant. The issue is you've assigned to `val` so it defaults to local — juanpa.arrivillaga, Jun 14 '19 at 21:43

score 1 · Answer 1 · answered Jun 14 '19 at 22:23

1

Use the nonlocal statement to make a variable defined in an enclosing function accesible inside the inner function, like so:

def func1():
    val = 1
    res = [1]
    def fun2():
        nonlocal val
        print(res)
        print(val)
        val = 2 
    fun2()
    print(val)

func1()

See also: earlier SO question.

answered Jun 14 '19 at 22:23

john-hen

4,410
2
23
40

1

Should note it's only in Python 3, since OP didn't say which version they're using. – Blorgbeard Jun 14 '19 at 23:04

score 0 · Answer 2 · answered Jun 14 '19 at 21:50

0

You can do it in the following way:

def func1():
    val = 1
    res = [1]
    def fun2(val=val, res=res):
        print(res)
        print(val)
        val = 2 
        return val
    val = fun2()
    print(val)

Output is then

>>> func1()
[1]
1
2

answered Jun 14 '19 at 21:50

WiseDev

524
4
17

How to make variable accessible inside another function

2 Answers2