返回 None 或元组并解包 [英] Returning None or a tuple and unpacking

问题描述

我总是对这个事实感到恼火:

I am always annoyed by this fact:

$ cat foo.py
def foo(flag):
    if flag:
        return (1,2)
    else:
        return None

first, second = foo(True)
first, second = foo(False)

$ python foo.py
Traceback (most recent call last):
  File "foo.py", line 8, in <module>
    first, second = foo(False)
TypeError: 'NoneType' object is not iterable

事实是，为了正确解包而不会遇到麻烦，我必须捕获 TypeError 或具有类似的东西

The fact is that in order to correctly unpack without troubles I have either to catch the TypeError or to have something like

values = foo(False)
if values is not None:
    first, second = values

这有点烦人.是否有改善这种情况的技巧(例如，将 first 和 second 都设置为 None 而没有 foo 返回(None，None))或有关我提出的案例的最佳设计策略的建议?*可能是变量?

Which is kind of annoying. Is there a trick to improve this situation (e.g. to so set both first and second to None without having foo returning (None, None)) or a suggestion about the best design strategy for cases like the one I present ? *variables maybe ?

推荐答案

好吧，你可以...

first,second = foo(True) or (None,None)
first,second = foo(False) or (None,None)

但据我所知，没有更简单的方法可以扩展 None 来填充整个元组.

but as far as I know there's no simpler way to expand None to fill in the entirety of a tuple.

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