考虑以下代码示例:
def testClosure():
count = 0
def increment():
count += 1
for i in range(10):
increment()
print(count)
调用它会导致:
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
我习惯用 C++ 编写这样的代码:
void testClosure() {
int count = 0
auto increment = [&](){
count += 1;
};
for (int i = 0; i < 10; ++i) {
increment();
}
}
我究竟做错了什么?不能从内部函数修改外部函数的局部变量吗?这些是不同类型的闭包(Python vs C++)吗?