[Python-ideas] PEP 505: None-aware operators

[Brice Parent]

Le 19/07/2018 à 10:36, Chris Angelico a écrit :
> On Thu, Jul 19, 2018 at 5:45 PM, Brice Parent <contact at brice.xyz> wrote:
>> The biggest drawback of this, is that (if I understand it well), it may be
>> done quite easily without any change to the language:
>>
>> def first_set(*elements):  # please don't mind the name of the function,
>> it's not the purpose here
>>      """ Will return the first element that is not None """
>>      for element in elements:
>>          if element is not None:
>>              return element
>>
>>      raise AllNoneException()
>>
>> first_set(3, 5)  # -> 3
>> first_set(None, 5)  # -> 5
>> first_set(None, None, 8, 10)  # -> 8
>> first_set(None, Car(model="sport")).buy()  # calling
>> Car(model="sport").buy()
>> first_set(None, ["a", "b", "c"])[1]  # -> "b"
>> first_set(None, None)  # -> exception is raised
>>
>> (note that such function could even accept a "rejected_values" kwarg, like
>> `rejected_values=(None, [], "")`, just by replacing the `if` clause by `if
>> element not in rejected_values:`)
> No it can't, for the same reason that the 'and' and 'or' operators
> can't be implemented cleanly as functions: it short-circuits. The
> right-hand operator _will not_ be evaluated unless the left is None.
>
> ChrisA
Thanks for the clarification, I didn't think about that.

It doesn't make it beautiful or easily readable, but at least, I 
understand how it may be useful then!