12.python-使用非当前作用域变量的方法

# 全局变量（global variable）& 非本地局部变量（nonlocal variable）
# 关键字global&nonlocal
# ===================================================


gcount = 0


def global_test():
    try:
        gcount += 1
        print(gcount)
    except Exception as e:
        print(str(Exception))  # <class 'Exception'>
        print(str(e))  # local variable 'gcount' referenced before assignment


print('Do not declare the global variable before changing it:')
global_test()


# 运行异常：
# UnboundLocalError: local variable 'gcount' referenced before assignment

# ===================================================
# 在函数内部 修改 全局变量之前，必须先再次声明全局变量，正确打开方式如下

def global_test_1():
    global gcount
    gcount += 1
    print(gcount)


print('Declare the global variable before changing it:')
global_test_1()  # 1


# ===================================================
# 若不修改全局变量，可不在局部声明全局变量

def global_test_2():
    print(gcount)


print('Needn\'t declare the global variable before referencing it:')
global_test_2()  # 1


# ===================================================
# 局部变量的用法


def outer():
    count = 0

    def inner():
        def inner_in():
            nonlocal count  # 修改非当前作用域且非全局变量，必须声明，若只是引用，不必声明
            count += 1
            return count

        return inner_in()

    return inner


inner_func = outer()
print(inner_func())  # 1
print(inner_func())  # 2
print(inner_func())  # 3

inner_func_1 = outer()
print(inner_func_1())  # 1
print(inner_func_1())  # 2
print(inner_func_1())  # 3