Python3中global/nonlocal用法

悠悠 2022-09-14 09:52 182阅读 0赞

**      全局变量(global variable)****是那些未在任何函数内部定义并且具有全局作用域的变量**，而**局部变量****(local variable)****是那些在函数内部定义并且其作用域仅限于该函数的变量**。换句话说，我们可以说局部变量只能在初始化它的函数内部访问，而全局变量在整个程序和每个函数内部都可以访问。

**      global关键字**：如果我们要进行赋值或更改全局变量，我们只需要在函数中使用global关键字。打印和访问全局变量不需要global关键字。如果在函数内部更改或创建的任何变量尚未声明为全局变量，则它都是局部变量。在函数外使用global关键字无效。global绑定全局变量。

**      nonlocal关键字**：与global关键字功能相似，但用于嵌套函数(nested function)中。nonlocal绑定局部变量，只对局部起作用，离开嵌套函数，那么该变量则无效。

**     ** 以上内容主要参考：[https://www.geeksforgeeks.org/global-local-variables-python/][https_www.geeksforgeeks.org_global-local-variables-python]

**     ** 以下为测试代码：

var = 6
    
    if var == 1:
        # reference: https://www.geeksforgeeks.org/global-local-variables-python/
        def f(): # Creating local variables
            s = "I love Geeksforgeeks" # local vairable
            print("Inside Function:", s)
    
        f()
        #print("s:", s) # NameError: name 's' is not defined
    elif var == 2:
        # reference: https://www.geeksforgeeks.org/global-local-variables-python/
        # Defining and accessing global variables
        def f(): # This function uses global variable s
            print("Inside Function:", s)
    
        # Global scope
        s = "I love Geeksforgeeks" # global variable,  is used both inside the f function as well as outside the f function
        f()
        print("Outside Function:", s)
    elif var == 3:
        # reference: https://www.geeksforgeeks.org/global-local-variables-python/
        # This function has a variable with name same as s
        def f():
            #s += 'GFG' # UnboundLocalError: local variable 's' referenced before assignment
            s = "Me too." # 如果在函数作用域内也定义了同名变量,那么它将仅打印函数内部给出的值,而不是全局值
            print(s)
    
        s = "I love Geeksforgeeks" # global scope
        f()
        print(s) # I love Geeksforgeeks
    elif var == 4:
        # reference: https://www.geeksforgeeks.org/global-local-variables-python/
        # This function modifies the global variable 's'
        def f():
            global s # 如果我们要进行赋值或更改全局变量,我们只需要在函数中使用global关键字
            s += ' GFG'
            print(s)
            s = "Look for Geeksforgeeks Python Section"
            print(s)
    
        s = "Python is great!" # global scope
        f()
        print(s) # Look for Geeksforgeeks Python Section
    elif var == 5:
        # reference: https://www.geeksforgeeks.org/use-of-nonlocal-vs-use-of-global-keyword-in-python/
        def fun():
            var1 = 10
    
            def gun():
                nonlocal var1 # tell python explicitly that it has to access var1 initialized in fun using the keyword nonlocal
                # global var1; var1 = var1 + 10 # NameError: name 'var1' is not defined
                var1 = var1 + 10
                print(var1) # 20
    
            gun()
            print(var1) # 20
    
        fun()
    elif var == 6:
        # reference: https://www.geeksforgeeks.org/python-nonlocal-keyword/
        def geek_func():
            geek_name = "geekforgeeks" # local variable to geek_func
    
            def geek_func1(): # First Inner function
                geek_name = "GeekforGeeks"
    
                def geek_func2(): # Second Inner function
                    nonlocal geek_name # Declairing nonlocal variable
                    geek_name = 'GEEKSFORGEEKS'
                    print(geek_name) # Printing our nonlocal variable, GEEKSFORGEEKS
    
                geek_func2() # Calling Second inner function
    
            geek_func1() # Calling First inner function
            print(geek_name) # Printing local variable to geek_func, geekforgeeks
    
        geek_func()
    print("test finish")

**      GitHub**：[https://github.com/fengbingchun/Python\_Test][https_github.com_fengbingchun_Python_Test]

[https_www.geeksforgeeks.org_global-local-variables-python]: https://www.geeksforgeeks.org/global-local-variables-python/
[https_github.com_fengbingchun_Python_Test]: https://github.com/fengbingchun/Python_Test