Python，UnboundLocalError：赋值前引用的局部变量'i'

Question

我正在尝试运行以下脚本：

i = 0
numbers = []

def number_includer(max_num):        

    while i < max_num:
        print "At the top i is %d" % i
        numbers.append(i)

        i = i + 1
        print "Numbers now: ", numbers
        print "At the bottom i is %d" % i

number_includer(7)


print "The numbers: "    

for num in numbers:
    print num

但当我这样做时：

numbers = []

def number_includer(max_num):
    # Used i equals 0 inside the function here.
    i = 0

    while i < max_num:
        print "At the top i is %d" % i
        numbers.append(i)

        i = i + 1
        print "Numbers now: ", numbers
        print "At the bottom i is %d" % i

number_includer(7)


print "The numbers: "    

for num in numbers:
    print num

我不想要回答而是一个解释，如果问题是在外部预定义的def内部使用局部变量，那么列表'数字'是全局的没有问题吗？