Using variables from another function in a function

Question

I have tried to search this but I don't quite understand. I am coming across this error so I formed a quick easy example.

def test():
    global a
    a = 0
    a+=1

def test2():
    a+=1
    print (a)


inp = input('a?')
if inp == 'a':
    test()
    test2()

When I input a. I expected the code to output 2. However, I get this error UnboundLocalError: local variable 'a' referenced before assignment. When I searched around about this, I found that you need to use global, but I already am using it.

So I don't understand. Can someone briefly explain what I'm doing wrong? Thanks.

What's the point of the input and if? How does it relate to the question? — Barmar
– Barmar, Commented Feb 8, 2018 at 19:21
Even better: try to avoid using global names, they break the modularity of the code. — PM 2Ring
– PM 2Ring, Commented Feb 8, 2018 at 19:21
No, it just says that within that function, a should refer to the global variable. — Barmar
– Barmar, Commented Feb 8, 2018 at 19:21
Couldn't you demonstrate it by just writing test() and test2() without the if? — Barmar
– Barmar, Commented Feb 8, 2018 at 19:22

Barmar · Accepted Answer · 2018-02-08 19:23:57Z

1

A global declaration only applies within that function. So the declaration in test() means that uses of the variable a in that function will refer to the global variable. It doesn't have any effect on other functions, so if test2 also wants to access the global variable, you need the same declaration there as well.

def test2():
    global a
    a += 1
    print(a)

answered Feb 8, 2018 at 19:23

Barmar

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Comments

destresa · Accepted Answer · 2018-02-08 19:26:53Z

1

1) You can return the modified value like:

def test():
    a = 0
    a+=1
    return a

def test2(a):
    a+=1
    print (a)


inp = input('a?')
if inp == 'a':
    a = test()
    test2(a)

2) Or you can use a class:

class TestClass:

    a = 0

    def test(self):
        self.a = 0
        self.a+=1

    def test2(self):
        self.a+=1
        print (self.a)

Usage of option 2:

>>> example = TestClass()
>>> example.test()
>>> example.test2()
2

answered Feb 8, 2018 at 19:26

destresa

1175 bronze badges

1 Comment

roganjosh Over a year ago

I think if you'd also explained why the original code didn't work then this would have been the better answer (not using global is almost always preferable) but it doesn't address what's actually not working in the original code.

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