python中合适的“什么都不做" lambda表达式? [英] A suitable 'do nothing' lambda expression in python?

问题描述

我有时会发现自己想让占位符不做任何事情" lambda表达式，类似于说:

I sometimes find myself wanting to make placeholder 'do nothing' lambda expressions, similar to saying:

def do_nothing(*args):
    pass

但是以下语法是非法的，因为lambda表达式试图返回冒号之后的内容，而您不能返回pass.

But the following syntax is illegal since lambda expressions attempt to return whatever is after the colon, and you can't return pass.

do_nothing = lambda *args: pass

所以我在想，下面的表达式是否可以替代上面的表达式?

So I was wondering, would the following expression be a suitable replacement for the above?

do_nothing = lambda *args: None

由于上面的do_nothing函数从技术上返回了None，因此可以制作一个返回None的lambda表达式用作占位符lambda表达式吗?还是不好的做法?

Since the do_nothing function above technically returns None, is it okay to make a lambda expression that returns None to use as a placeholder lambda expression? Or is it bad practice?

推荐答案

此:

def do_nothing(*args):
    pass

等效于:

lambda *args: None

有一些细微的区别，一个是lambda，一个不是. (例如，函数上的__name__将是do_nothing，而在lambda上将是<lambda>.)如果您觉得很重要，请不要忘记**kwargs. Python中没有显式return <x>的函数将返回None.这是此处:

With some minor differences in that one is a lambda and one isn't. (For example, __name__ will be do_nothing on the function, and <lambda> on the lambda.) Don't forget about **kwargs, if it matters to you. Functions in Python without an explicit return <x> return None. This is here:

除非总是引发异常，否则调用始终返回一些值，可能为无.

A call always returns some value, possibly None, unless it raises an exception.

我使用类似的功能作为默认值，例如:

I've used similar functions as default values, say for example:

def long_running_code(progress_function=lambda percent_complete: None):
    # Report progress via progress_function.

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