Why doesn't this closure modify the variable in the enclosing scope?

Question

This bit of Python does not work:

def make_incrementer(start):
    def closure():
        # I know I could write \'x = start\' and use x - that\'s not my poi         


        

Answer 1

In Python 3.x you can use the nonlocal keyword to rebind names not in the local scope. In 2.x your only options are modifying (or mutating) the closure variables, adding instance variables to the inner function, or (as you don't want to do) creating a local variable...

# modifying  --> call like x = make_incrementer([100])
def make_incrementer(start):
    def closure():
        # I know I could write 'x = start' and use x - that's not my point though (:
        while True:
            yield start[0]
            start[0] += 1
    return closure

# adding instance variables  --> call like x = make_incrementer(100)
def make_incrementer(start):
    def closure():
        while True:
            yield closure.start
            closure.start += 1
    closure.start = start
    return closure

# creating local variable  --> call like x = make_incrementer(100)
def make_incrementer(start):
    def closure(start=start):
        while True:
            yield start
            start += 1
    return closure