两段代码如下，求教为什么L作为list时候可以正常使用，L作为int的时候就要内外都声明global才能行呢？

def createCounter():
    L = []
    def counter():
        L.append('')
        return len(L) 
    return counter
    
counterA = createCounter()
print(counterA(), counterA(), counterA(), counterA(), counterA()) # 1 2 3 4 5
counterB = createCounter()
if [counterB(), counterB(), counterB(), counterB()] == [1, 2, 3, 4]:
    print('测试通过!')
else:
    print('测试失败!')

def createCounter():
    global L
    L = 0
    def counter():
        global L
        L = L +1
        return L
    return counter

counterA = createCounter()
print(counterA(), counterA(), counterA(), counterA(), counterA()) # 1 2 3 4 5
counterB = createCounter()
if [counterB(), counterB(), counterB(), counterB()] == [1, 2, 3, 4]:
    print('测试通过!')
else:
    print('测试失败!')