PEP 308: A PEP Writer's Experience - PRO

[Anders J. Munch]

"Andrew Dalke" <adalke at mindspring.com> wrote:
>   rate if/else could be used == 1 every 400 LOC
>   rate it would be used == 1 every 1,000 LOC
>   rate where short circuiting is needed == 1 every 5,000 LOC
>   rate if/else expression used in an if statment == 1 every 10,000 LOC
>   rate where "something and this or that"
>       would not suffice (larger uncertainty here)  == 1 every 25,000 LOC
>   rate used as "if (if something: this else: that)" == 1 every 40,000 LOC
> 
> It's remarkably easy to do this sort of analysis using grep and
> a reasonably large C/C++ codebase.  Several appropriate codebases
> are available to you.

To every hard problem, there's a solution that is simple, obvious, and
wrong.  (Sorry, couldn't resist.)

Your searches are all single-line.  Conditional expressions broken
over multiple lines are not uncommon.

In my personal use, conditional expressions are used a lot in
debugging diagnostics, which are later deleted.  The frequency of
conditionals in any codebase snapshot may not reflect the frequency of
using conditionals.

> 
> So again I ask you, what rate of misuse is low enough as to
> not be a problem?  1%?  10%?  50%?  0.01%?  Apparently
> it's above 3%.

No examples I have seen so far qualify for the strong term "misuse".
Bad style perhaps, though I'm not even sure that

>    if (something ? this : that) ...

is bad style.  Can you suggest an alternative?  The only semantically
neutral rewrite I can think of is

     bool something_var = something;
     if((something_var && this) || (!something_var && that))

which I'd hesitate to call an improvement.

>[...]and I include
> cases where the if/else expression will be used in lieu of better/
> more appropriate cases, as in "x = (if obj: obj else: default)"
> instead of "x = obj or default".

  "x = (if obj: obj else: default)"

is fine.  In all likelyhood whoever wrote this is unfamiliar or
uncomfortable with "obj or default", and would not have used that
anyway.  Also, it lends itself to a clarification such as

  "x = (if obj is None: obj else: default)"

- Anders