Python中的空模式不足吗？ [英] Null pattern in Python underused?

问题描述

每次我都会遇到这样的代码：

Every now and then I come across code like this:

foo = Foo()
...
if foo.bar is not None and foo.bar.baz == 42:
   shiny_happy(...)

对于我来说，这似乎是一个愚蠢的事情。

Which seems, well, unpythonic, to me.

在Objective-C中，您可以发送消息到nil，答案。我一直认为这是非常方便的。当然，可以从Google给出的结果判断 Python中的空格式我，似乎这不是很广泛的使用。为什么是这样？

In Objective-C, you can send messages to nil and get nil as the answer. I've always thought that's quite handy. Of course it is possible to implement a Null pattern in Python, however judging from the results Google's given me, it seems this is not very widely used. Why's that?

或者甚至更好 - 这是一个坏主意，让None.whatever返回None而不是提出异常？

Or even better—would it be a bad idea to let None.whatever return None instead of raising an exception?

推荐答案

PEP 336 - Make None Callable 提出了一个类似的功能：

PEP 336 - Make None Callable proposed a similar feature:

没有应该是一个可调用对象，当用任何参数调用
没有副作用并返回无。

None should be a callable object that when called with any arguments has no side effect and returns None.

为什么被拒绝的原因只是被认为是无提出调用时发生错误。

The reason for why it was rejected was simply "It is considered a feature that None raises an error when called."

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