[Python-ideas] add fluent operator to everything

[Steven D'Aprano]

On Thu, Feb 21, 2019 at 12:55:00PM +1100, Steven D'Aprano wrote:
> On Wed, Feb 20, 2019 at 10:24:25AM -0800, Bruce Leban wrote:
> 
> > Here's a syntax that solves this using the new operators _:= and ,_
> 
> Be careful about making such dogmatic statements.

Ah, I have just spotted your later explanation that you aren't referring 
to *new operators* spelled as _:= and ,_ (as I understood from your 
words) but as *existing syntax* that works today (at least in the most 
up-to-date version of 3.8).

That pretty much makes all my previous objections to these "new 
operators" redundant, as they aren't operators at all.

I'll point out that there's nothing special about the use of an 
underscore here. Instead of your snippet:

    _:= a ,_ .append(4) ,_ .sort()

we could write:

   tmp := a, tmp.append(4), tmp.sort()

So this is hardly method chaining or a fluent interface. (Hence my 
confusion -- I thought you were suggesting a way to implement a fluent 
interface.)

If this were an Obfuscated Python competition, I'd congratulate you for 
the nasty trick of putting whitespace in non-standard positions to 
conceal what is going on. But in real code, that's only going to cause 
confusion.

(But I think you acknowledge that this trick is not easy to read.)

But it's also sub-optimal code. Why introduce a temporary variable 
instead of just writing this?

    a.append(4), a.sort()

The only advantage of _ is that it is a one-character name. But there 
are other one character names which are less mystifying:

    a := some_long_identifier, a.append(4), a.sort()

But why create a tuple filled mostly with None? Python is slow enough as 
it is without encouraging such anti-patterns.

    a := some_long_identifier; a.append(4); a.sort()

Now no tuple is created, and doesn't need to be garbage collected.

But this is still not a fluent interface. Its just cramming multiple 
statements into a single line. Which means you can't do this:

    function(arg1, mylist.append(1).sort(), arg3)




-- 
Steven