Readability counts, was Re: Use of Lists, Tupples, or Sets in IF statement.

[Peter Otten]

Rustom Mody wrote:

> On Tuesday, March 15, 2016 at 2:00:25 PM UTC+5:30, Peter Otten wrote:
>> Rustom Mody wrote:
>> 
>> > Others have answered some parts
>> >>>> if x in x_list:
>> > ...     print("That is a fruit.")
>> > ... else:
>> > ...     print("That is not a fruit.")
>> > ...
>> > 
>> > However one can distribute the print out of the if; Thus
>> > 
>> >>>> "This is %s a fruit" % ("" if x in x_list else "not")
>> 
>> Which of the two versions will most readers grasp at first sight?
>> Which one is easier to modify so that it works for arbitrary attributes?
>> Which one is easier to internationalize?
> 
> I think you are saying that my (last) version is clever in a rather stupid
> sort of way. Yes?

Well, yes ;)

> Well if that is what someone recommends for serious programming then
> guilty as charged
> 
> But there is a world of difference between
> - What one SHOULD (or not) do
> - What one CAN do
> 
> The first is about serious|professional software engineering
> The second is about getting an education beyond basic to some more
> familiarity
> 
> I assumed that OP is in the noob stage and was welcome some learning.
> So what I wanted to convey is not so much that such expressions are nice
> to have in serious code. Rather that
> 1. Like algebra has laws so does programming
> 2. That these laws can be used to massage one program into another
> 3. That expressions (like %-format) can occur elsewhere than in prints

That (the % part) is a lesson for C programmers rather than newbies ;)

> 4. That prints are usually unnecessary (and an abomination)

They aren't. They are often misused by beginners when they occur where a 
function should return a value.
 
> Not that 3 and 4 come out so well as 1,2 in the above example.
> 
> However to answer your questions specifically.
> 
> Internationalization: Terrible
> Arbitrary attributes: not sure what you are referring to
> Readability: Very much like beauty -- in the eye of the beholder
> Some things are universally beautiful; some only in some cultural contexts
> Likewise readability
> 
> Partly people find if-expressions unreadable because they are not used to
> them.
> This is backward because expressions are as basic than statements  -- if
> anything more basic.

I think the problem is not that you prefer a programming paradigm that is 
not Python's default -- it's that you crammed too many ideas into one 
example. It's probably most helpful to concentrate on your main point, e. g.

(You can) Use an expression:

>>> x = "flying saucer"
>>> "This is a fruit" if x in x_list else "This is not a fruit"
'This is not a fruit'

> It is *symmetric*  Unfortunately understood as lopsided
> More such symmetries in this table:
> http://blog.languager.org/2016/01/primacy.html#expstat
> 
> Partly python if-expressions are unreadable because they are backward
> compared to if-statements. A minor syntactic nuisance but yes it does
> impact readability

Indeed. It's still better than

"This is %s a fruit" % (x in x_list and "" or "not")

The bug is intentional; the fix is of course

"This is %s a fruit" % (x in x_list and "most likely" or "probably not")

;)