函数内是可以直接打印外面的变量？！ 但是却不能运算？！

import os



def printdrink():

    print("drink:", drink[i])

    #test+=1 会报错，屏蔽

    print(test)





test = 111



drink =['coffee','black_tea','milk_tea','cococa','water']

print("type drink: ",type(drink))

for i in range(len(drink)):

    printdrink()

结果 

type drink:  <class 'list'>
drink: coffee
111
drink: black_tea
111
drink: milk_tea
111
drink: cococa
111
drink: water
111

另外这个test在函数内并不能 test+=1 会报错 local variable 'test' referenced before assignment ？！ 意思说我使用了一个没初始值的局部变量 ？

如果代码改为

import os



def printdrink(test):

    print("drink:", drink[i])

    test+=1

    print(test)





test = 111



drink =['coffee','black_tea','milk_tea','cococa','water']

print("type drink: ",type(drink))

for i in range(len(drink)):

    printdrink(test)

这样函数里面永远都是打印112.这代表了这个test只是值传递。有没有办法强制引用传递呢？