Python函数无法访问全局变量？

Question

我熟悉Java和JS等其他语言，并且刚学过Python，这让我感到困惑：

upper_case = 0
lower_case = 0

s = "Hello"

def upper_lower(s):
    for c in s:
        if c.islower():
            lower_case += 1
        elif c.isupper():
            upper_case += 1
    print(upper_case, lower_case)

但是我总是遇到错误UnboundLocalError: local variable 'upper_case' referenced before assignment “分配前的参考”是什么意思？但是我已经在全局变量之前声明了这个变量？

Answer 1

您可以做到

s = "Hello"

def upper_lower(s):
    upper_case = 0
    lower_case = 0
    for c in s:
        if c.islower():
            lower_case += 1
        elif c.isupper():
            upper_case += 1
    print(upper_case, lower_case)

或如global关键字所述

Answer 2

在函数内部，您需要使用global关键字。

upper_case = 0
lower_case = 0

s = "Hello"

def upper_lower(s):
    global upper_case
    global lower_case
    for c in s:
        if c.islower():
            lower_case += 1
        elif c.isupper():
            upper_case += 1
    print(upper_case, lower_case)

Answer 3

您必须添加全局

upper_case = 0
lower_case = 0

s = "Hello"

def upper_lower(s):

    global upper_case
    global  lower_case

    for c in s:
        if c.islower():
            lower_case += 1
        elif c.isupper():
            upper_case += 1
    print(upper_case, lower_case)


upper_lower(s)

结果

1 4

Answer 4

该错误是因为您尝试执行以下操作：lower_case += 1，与lower_case = lower_case +1相同。由于lower_case没有初始值，因此无法执行此操作。解决方法是添加以下两行：

    upper_case = 0
    lower_case = 0

您应该这样做：

upper_case = 0
lower_case = 0

s = "Hello"

def upper_lower(s):
    upper_case = 0
    lower_case = 0
    for c in s:
        if c.islower():
            lower_case += 1
        elif c.isupper():
            upper_case += 1
    print(upper_case, lower_case)

upper_lower(s)