How to define global variables and local variables in Python?

In Python, global variables and local variables are defined as follows:

1. Global variables are variables that can be accessed and modified within the entire program, they can be defined outside of any function in the program.

global_variable = 10  # 全局变量

def function():
    # 访问全局变量
    print(global_variable)
    
    # 修改全局变量
    global global_variable
    global_variable = 20
    
function()  # 输出：10
print(global_variable)  # 输出：20

1. Local variables: These are variables defined within a function and can only be accessed and modified within that function. Their scope is limited to the function in which they are defined.

def function():
    local_variable = 10  # 局部变量
    print(local_variable)
    
function()  # 输出：10
print(local_variable)  # 报错，局部变量不可在函数外部访问

It is important to note that if you need to modify a global variable within a function, you must use the “global” keyword to declare the variable as global within the function. Otherwise, Python will consider it as a local variable.