在python中带括号和不带括号的调用函数有什么区别? [英] What is the difference between calling function with parentheses and without in python?

问题描述

我有一个问题.让我们假设我们有函数 hello().带括号和不带括号有什么区别?当我调用 hello() 时，它指的是一个值等于这个函数的对象.或者也许我错了?当我不带括号调用它时会发生什么?

I have a question. Lets assume that we have function hello(). What is the difference between calling it with parentheses and without? When I call hello() it is referring to an object with value equals this function. Or maybe am I wrong? What happens when I call it without parentheses?

不知道为什么

def hello():
    pass

print(id(hello))
print(id(hello()))

返回不同的结果

4400606744
4398942536

推荐答案

简答:见 https://nedbatchelder.com/text/names.html 以更好地了解对象和用于指代对象的名称之间的区别.

Short answer: see https://nedbatchelder.com/text/names.html to get a better understanding of the difference between objects and the names used to refer to objects.

当且仅在使用括号时调用函数.hello() 调用函数；hello 只是一个绑定到函数的名称，例如，可以用来将函数对象作为参数传递给另一个函数.

A function is called if and only if you use parentheses. hello() calls the function; hello is simply a name bound to the function, and can be used, for example, to pass the function object as an argument to another function.

def caller(f):
    f()

def hello():
    print("hi")

def goodbye():
    print("bye")

caller(hello)  # Prints "hi"
caller(goodbye)  # Prints "bye"

<小时>

关于您的更新，id 返回不同的值，因为对 id 的每次调用都会接收一个完全独立的对象作为其参数.使用 id(hello)，id 获取函数对象本身.使用id(hello())，id 正在通过调用hello 获取返回的对象；和

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Regarding your update, id returns different values because each call to id receives a completely separate object as its argument. With id(hello), id gets the function object itself. With id(hello()), id is getting the object returned by the call to hello; it's the same as

x = hello()
print(id(x))

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