嵌入式函数中的全局变量

Question

I have the following snippet:

def test ():
  num_sum = 0
  def inner_test ():
    global num_sum
    num_sum += 1
  inner_test()
return num_sum

When I run test() I get:

NameError: name 'num_sum' is not defined

I was expecting that the inner function would change the value of the num_sum variable defined in the outer function. Basically, I need a global variable to increment in an inner function which I may call recursively.

I noticed that this pattern works well with collections (lists, dictionaries) even if I don't define the variable as global (but pass it as a parameter to the inner function).

However, with scalar values like int this pattern seems to break. Neither defining the variable as global (as is here) nor passing it as a parameter to the inner function works as intended. Basically, the scalar variable stays unchanged. What do I need to do to get the desired behaviour with such scalar values?

Answer 1

you need nonlocal instead of global . your num_sum is not a global variable (will not be found in globals() ). nonlocal will instruct python not to search for it in the global namespace, but in the nearest namespace. the order is LEGB: Local, Enclosed, Global, Built-in .