[Python-ideas] kwargs for return

[Thomas Güttler]

Wow, thank you very much for all those answers and hints to my message.

David opened my eyes with this: Functions return a single value, period.

Yes, this means my question is not about a function, it is about assignment.

Dictionary unpacking could be used for my use case.

Since it does not exist, I will look at dataclasses.

Thank you very much for your feedback.

   Thomas Güttler


Am 26.01.19 um 14:04 schrieb Thomas Güttler Lists:
> I know this is going to get rejected, but I want to speak out the idea nevertheless:
> 
> I love kwargs and named arguments from the beginning (roughly 18 years now)
> 
> I guess you came across this several times before:
> 
> In the first version of the API one variable gets returned:
> 
> Example:
> 
> 
>      status = backend.transmit_data()
> 
> But later you want to add something to the API.
> 
> 
> For the input part of a method this is solved. You
> can add an optional kwarg.
> 
> But for the output part of a method, there you can't change
> the interface easily up to now.
> 
> Use case: you want to add an optional list of messages which
> could get returned.
> 
> You want to change to
> 
>      status, messages = backend.transmit_data()
> 
> If you have 10 different backend implementations,
> then you need to change all of them.
> 
> This is difficult, if the backends reside in different
> repos and maybe you even don't own some of these repos.
> 
> Current draw-back: you need to change all of them at once.
> 
> Of course you could work around it be using this
> 
>     status_messages = backend.transmit_data()
> 
> And then do some fancy guessing if the variable contains
> only the status or a tuple containing status and messages.
> 
> Some days ago I head the idea that kwargs for return would
> help here.
> 
> 
> This should handle both cases:
> 
> Case1: The old backend returns only the status, and the caller
> wants both status and messages. Somehow the default
> for messages needs to be defined. In my case it would
> be the empty list.
> 
> 
> Case2: The new backends returning the status
> and messages. The old caller just gets the
> status. The messages get discarded.
> 
> Above is the use case.
> 
> How could kwargs for return look like?
> 
> Maybe like this:
> 
> .....
> 
> Sorry, I could not find a nice, clean and simple syntax
> for this up to now.
> 
> Maybe someone else is more creative than I am.
> 
> What do you think about this?
> 
> 
> Regards,
>    Thomas Güttler
> 
> 
> -- 
> Thomas Guettlerhttp://www.thomas-guettler.de/
> I am looking for feedback:https://github.com/guettli/programming-guidelines
> 
> 
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-- 
Thomas Guettler http://www.thomas-guettler.de/
I am looking for feedback: https://github.com/guettli/programming-guidelines