Modify the function variables from inner function in python

Question

It's ok to get and print the outer function variable a

def outer():
    a = 1
    def inner():
        print a

It's also ok to get the outer function array a and append something

def outer():
    a = []
    def inner():
        a.append(1)
        print a

However, it caused some trouble when I tried to increase the integer:

def outer():
    a = 1
    def inner():
        a += 1 #or a = a + 1
        print a

>> UnboundLocalError: local variable 'a' referenced before assignment

Why does this happen and how can I achieve my goal (increase the integer)?

@sberry: That will not allow what he's trying to do, since it will create a new local variable inside inner, changes to which will not be reflected in outer. — BrenBarn
– BrenBarn, Commented Dec 21, 2012 at 7:04
Right, unless it is returned, or the OP only has use of a within inner anyway. — sberry
– sberry, Commented Dec 21, 2012 at 7:06

BrenBarn · Accepted Answer · 2012-12-21 07:01:10Z

6

In Python 3 you can do this with the nonlocal keyword. Do nonlocal a at the beginning of inner to mark a as nonlocal.

In Python 2 it is not possible.

answered Dec 21, 2012 at 7:01

BrenBarn

253k39 gold badges421 silver badges392 bronze badges

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

1 Comment

Fr0sT Jan 24 at 14:50

The only direct and correct answer here... Thx!

codeape · Accepted Answer · 2012-12-21 07:43:53Z

3

Workaround for Python 2:

def outer():
    a = [1]
    def inner():
        a[0] += 1
        print a[0]

answered Dec 21, 2012 at 7:43

codeape

102k26 gold badges180 silver badges201 bronze badges

Comments

Jakob S. · Accepted Answer · 2012-12-21 07:04:18Z

3

A generally cleaner way to do this would be:

def outer():
    a = 1
    def inner(b):
        b += 1
        return b
    a = inner(a)

Python allows a lot, but non-local variables can be generally considered as "dirty" (without going into details here).

answered Dec 21, 2012 at 7:04

Jakob S.

1,8912 gold badges15 silver badges29 bronze badges

Collectives™ on Stack Overflow

Modify the function variables from inner function in python

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related