[Python-Dev] (name := expression) doesn't fit the narrative of PEP 20

[Steven D'Aprano]

On Wed, Apr 25, 2018 at 10:14:11PM -0700, Łukasz Langa wrote:

> So only use the Pascal one in expressions. But don't forget 
> parentheses, otherwise it will bind the thing you probably didn't want 
> anyway.

Binding expressions are no worse than any other expression: sometimes 
you need to bracket terms to change the default precedence, and 
sometimes you don't.

And sometimes, even if we don't *need* parens, we use them anyway 
because it makes the expression easier to read and understand.

Unless you have a language with no operator precedence at all, a purely 
left-to-right evaluation order like Forth or (I think?) APL, there will 
always be circumstances where parens are needed. Criticising binding- 
expressions for that reason, especially implying that we must always use 
parens, is simply FUD.


[...]
> As soon as we have to wrap a part of an expression in parentheses, 
> parsing the entire thing becomes more complex.

Unless it becomes less complex to read and understand.

I for one always have difficulty parsing complex boolean tests unless I 
bracket some or all of the parts, even when they're not strictly needed. 
Consequently I try very hard not to write complex bool tests in the 
first place, but when I can't avoid it, a few extra brackets really 
helps simplify the logic.


> Often enough it will 
> cause the expression to exceed whatever line length limit the codebase 
> pledged not to exceed, causing one line to become three.

Just how often are your lines within two characters of the maximum 
column so that adding a pair of brackets () will "often enough" put it 
over the limit? Seems pretty unlikely to me. This sounds really like 
picking at straws.


-- 
Steve