PEP 308: A PEP Writer's Experience - PRO

[Bengt Richter]

On Sun, 9 Feb 2003 17:30:03 GMT, Andrew Koenig <ark at research.att.com> wrote:

>Gerrit> I disagree, because maybe both X and Y are in all cases a bad
>Gerrit> way to write it, so that it's not necessary to enlarge the
>Gerrit> language so that X can be written as Y if Z is still better.
>
>Here's a different example that you may find more persuasive.
>
>Recall that many programs take file names as parameters, and some of
>those use the convention that if the file name is "-", the program
>should process the standard input instead of opening a file.
>
>Suppose we want to print the identity of the file that we are about to
>process.  In other words, we want to print "Processing", followed by
>either "<stdin>" or the file name, depending on whether the
>file name is "-".
>
>Then I would like to be able to write this:
>
>    print "Processing", "<stdin>" if filename == "-" else filename
>
To me, that reads like

     print "Processing", "<stdin>" if filename == "-"
     else filename

i.e., I am used to if-else selecting alternative actions, not alternative data,
so the first action candidate is print something, and the else action candidate
is <cognitive dissonance here>. I.e., the else reads as if introducing the
alternative to print (an action), not to "<stdin>" (data).

I'd rather have

     print "Processing", (filename == "-" ? filename, "<stdin>") # (cond ? sel_F, sel_T)

With a multiway integer selection spelled iexpr ?? sel0, sel1, sel2 # etc
        
>You might claim that it is better to write
>
>    print "Processing",
>    if filename == "-":
>        print "<stdin>"
>    else:
>        print filename
>
>or, alternatively, to write
>
>    if filename == "-":
>        printname = "<stdin>"
>    else:
>        printname = filename
>    print "Processing", printname
>
>or, perhaps,
>
>    def printname(filename):
>        if filename == "-":
>            return "<stdin>"
>        return filename
>    print "Processing", printname(filename)
>
>but I disagree.  I think it's premature factoring.  The time to factor
Good to have a name for it ;-)

>out the concept of "the printable version of a filename" is when you
>know you're going to use it more than once (and possibly more than
>twice).
>

>Of course, I don't consider this argument to be proof.  There isn't
>going to be any proof in this discussion, because the whole question
>is *always* about which of two equivalent forms to prefer.
Or three, or more ;-)

Regards,
Bengt Richter