[Python-ideas] With expressions

[Steven D'Aprano]

On Sat, Aug 04, 2018 at 12:28:40AM +0200, Robert Vanden Eynde wrote:

> As the code I showed, being just that:
> 
> filename = ...
> lines = ...
> parsed_data = ...
> 
> With implementation details? The highest value is there, the alg is clear.,
> one fetches the filename, one preprocess the lines, then parse the data.

As programmers, surely we have to care about implementation details of 
the code we are maintaining or writing. If we don't care about 
implementation, who does?

Of course there is a tension between having to deal with implementation 
details too earlier, or hiding them too deeply. We have to balance too 
little refactoring from too much refactoring, and people can 
legitimately disagree as to when a function, method or class carries its 
own weight.

The same applies to syntactic features. That's why *concrete use-cases* 
are important, not pretend, made-up toy examples.

The Python community as a whole is not very receptive to arguments from 
functional programming purity. I know Python veterans who still don't 
like list comprehensions (although they're a minority). As a whole, the 
community does not believe that using multiple statements is always a 
problem to be fixed.

The question is not whether it is *possible* to have a with expression, 
or whether we might find some toy examples that kinda look good, but how 
much it improves *real code*.

And arguments that we should have a "with" expression because we already 
have "if" expressions and comprehensions will just fall flat. Arguments 
by consistency ("we have A, so we ought to have E too, because they're 
both vowels") are not very productive.


-- 
Steve