How to modify local variables from a nested closure? [duplicate]

StackOverflow https://stackoverflow.com/questions/17726424

문제

Consider the following code example:

def testClosure():
    count = 0

    def increment():
        count += 1

    for i in range(10):
        increment()

    print(count)

Calling this results in: 

Traceback (most recent call last):
  File "/Users/cls/workspace/PLPcython/src/sandbox.py", line 23, in <module>
    testClosure()
  File "/Users/cls/workspace/PLPcython/src/sandbox.py", line 18, in testClosure
    increment()
  File "/Users/cls/workspace/PLPcython/src/sandbox.py", line 15, in increment
    count += 1
UnboundLocalError: local variable 'count' referenced before assignment

I am used to code like this working in C++:

void testClosure() {
    int count = 0

    auto increment = [&](){
        count += 1;
    };

    for (int i = 0; i < 10; ++i) {
        increment();
    }

}

What am I doing wrong? Is it not possible to modify local variables of the outer function from an inner function? Are these different types of closures (Python vs C++)?

도움이 되었습니까?

해결책

I got it working if you do this:

def testClosure():
    count = 0

    def increment():
        nonlocal count
        count += 1

    for i in range(10):
        increment()

    print(count)
testClosure()

Note this will only work in Python 3.x, but you are clearly using that so it isn't a problem.

라이센스 : CC-BY-SA ~와 함께 속성
제휴하지 않습니다 StackOverflow
scroll top