How is variable scope defined in Python?

How is variable scope defined in Python?

In Python, the scope of a variable refers to the scope in which the variable takes effect, that is, the scope in which the variable can be accessed and manipulated. Variable scope in Python is divided into two types: global scope and local scope.

Global scope refers to variables that can be accessed and manipulated throughout the program. In Python, global scope variables are usually defined at the outermost level of the program, and they can be accessed and referenced inside functions or other code blocks. Global scope variables can be used anywhere in the entire program.

The following is an example of global scope:

x = 10

def func():
    print(x)

func()  # 输出：10

In the above code, the variable x is accessed inside the function func, and it It is defined outside the function, so it belongs to the global scope. Therefore, the variable x can be accessed in function func and its value can be output.

Local scope refers to variables defined inside a function and can only be accessed and operated inside the function. Its scope is limited to the function in which it is defined. Once the function execution is completed, the local scope variables will be destroyed.

The following is an example of local scope:

def func():
    y = 20
    print(y)

func()  # 输出：20
print(y)  # 报错：NameError: name 'y' is not defined

In the above code, the variable y is defined inside the function func, it Belongs to local scope. Therefore, the variable y can be accessed inside the function and its value can be output. However, when we try to access variable y outside the function, an error will be reported.

In Python, when a variable is assigned a value inside a function, Python treats the variable as a local variable by default. However, if we want to refer to a variable in the global scope within a function, we can use the global keyword to declare the variable.

Here is an example of using the global keyword:

x = 10

def func():
    global x  # 声明变量x为全局变量
    x = 20
    print(x)

func()  # 输出：20
print(x)  # 输出：20

In the above code, we use inside the function func The global keyword declares variable x as a global variable. In this way, after the value of variable x is modified inside the function, the value of variable x in the global scope will also change accordingly.

To summarize, variable scope in Python is divided into global scope and local scope. Global scope variables can be accessed and manipulated anywhere in the entire program, while local scope variables are limited to use within functions. If you need to refer to a variable in the global scope within a function, you can use the global keyword to declare it. Understanding variable scope is important for writing clearly structured and maintainable Python code.

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