Accessing a Variable from Within a Doubly Nested Function in Python

Question

The following code:

x = 0
print "Initialization: ", x
def f1():
    x = 1
    print "In f1 before f2:", x
    def f2():
        global x
        x = 2
        print "In f2:          ", x
    f2()
    print "In f1 after f2: ", x
f1()
print "Final:          ", x

prints:

Initialization:  0
In f1 before f2: 1
In f2:           2
In f1 after f2:  1
Final:           2

Is there a way for f2 to access f1's variables?

This is a dreadful thing. Why are you trying to do this? Why not just make f1 a callable object and properly share instance variables? — S.Lott
– S.Lott, Commented Feb 18, 2010 at 18:48
I agree, it is very dreadful, but I was wondering if it was possible. I would hope that nobody would put something like this out in the wild. — kzh
– kzh, Commented Feb 19, 2010 at 14:26

nikow · Accepted Answer · 2010-02-18 17:30:40Z

6

You can access the variables, the problem is the assignment. In Python 2 there is no way to rebind x to a new value. See PEP 227 (nested scopes) for more on this.

In Python 3 you can use the new nonlocal keyword instead of global. See PEP 3104.

edited Feb 18, 2010 at 17:30

answered Feb 18, 2010 at 17:25

nikow

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Comments

interjay · Accepted Answer · 2010-02-18 17:25:11Z

6

In Python 3, you can define x as nonlocal in f2.

In Python 2, you can't assign directly to f1's x in f2. However, you can read its value and access its members. So this could be a workaround:

def f1():
    x = [1]
    def f2():
        x[0] = 2
    f2()
    print x[0]
f1()

answered Feb 18, 2010 at 17:25

interjay

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Comments

SilentGhost · Accepted Answer · 2010-02-18 17:24:34Z

0

remove global statement:

>>> x
0
>>> def f1():
    x = 1
    print(x)
    def f2():
        print(x)
    f2()
    print(x)


>>> f1()
1
1
1

if you want to change variable x from f1 then you need to use global statement in each function.

answered Feb 18, 2010 at 17:24

SilentGhost

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2 Comments

interjay Over a year ago

That won't allow you to assign to x from f2.

SilentGhost Over a year ago

that was fixed, interjay. However, from the question it is not clear that OP wants to assign to x. He says access.

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