python - 嵌套函数如何在 Python 中工作？

Question

def maker(n):
    def action(x):
        return x ** n
    return action

f = maker(2)
print(f)
print(f(3))
print(f(4))

g = maker(3)
print(g(3))

print(f(3)) # still remembers 2

为什么嵌套函数记住第一个值 2 即使 maker() 已经返回并在 action() 时退出叫什么？

Answer 1

你基本上是在创建一个 closure .

In computer science, a closure is a first-class function with free variables that are bound in the lexical environment. Such a function is said to be "closed over" its free variables.

相关阅读:Closures: why are they so useful?

A closure is simply a more convenient way to give a function access to local state.

来自 http://docs.python.org/reference/compound_stmts.html :

Programmer’s note: Functions are first-class objects. A 'def' form executed inside a function definition defines a local function that can be returned or passed around. Free variables used in the nested function can access the local variables of the function containing the def. See section Naming and binding for details.