Python knowledge points: How to modify the value of a global variable in a function?

Variables defined outside of functions are global variables.

Global variables can be read in functions, but by default the values ​​of variables cannot be modified in functions.

can read

The following code can successfully print the number of fans in the function, because the function can read the value of the global variable:

count = 30888 #全局变量，麦叔粉丝数

# 关注
def guanzhu():
    print('麦叔的粉丝数是{}'.format(count))

# 取关
def quguan():
    print('麦叔的粉丝数是{}'.format(count))

Can not be modified

The following code will report an error, because the function cannot modify the value of the global variable by default:

count = 30888 #麦叔粉丝数

# 关注
def guanzhu():
    count = count + 1
    print('麦叔的粉丝数是{}'.format(count))

# 取关
def quguan():
    count = count - 1
    print('麦叔的粉丝数是{}'.format(count))

Use the global keyword

In order to modify the value of a global variable in a function, you need to use the global keyword to declare the variable as a global variable at the beginning of the function.

This can be modified like this:

count = 30888 #麦叔粉丝数

# 关注
def guanzhu():
    global count
    count = count + 1
    print('麦叔的粉丝数是{}'.format(count))

# 取关
def quguan():
    global count
    count = count - 1
    print('麦叔的粉丝数是{}'.format(count))

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