Path: csiph.com!usenet.pasdenom.info!news.etla.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed2a.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
MIME-Version: 1.0
In-Reply-To: <2633c4d3-e8cc-47fa-b22a-48dab2ef1a29@googlegroups.com>
References: <27ac2248-0ca3-4ba6-9d25-eaad324bc5e9@googlegroups.com> <bd36a46b-d704-4eb1-9b7d-1308d1fb6699@googlegroups.com> <mailman.7435.1393523704.18130.python-list@python.org> <5f4f5a5f-327a-4616-8235-17ee9e74c488@googlegroups.com> <530fef58$0$11113$c3e8da3@news.astraweb.com> <e24e0817-67d1-4dbd-b3ba-9250e735d261@googlegroups.com> <mailman.7453.1393562612.18130.python-list@python.org> <871tynznpd.fsf@elektro.pacujo.net> <53104798$0$11113$c3e8da3@news.astraweb.com> <mailman.7460.1393577227.18130.python-list@python.org> <87ha7jy2qs.fsf@elektro.pacujo.net> <5310b031$0$29985$c3e8da3$5496439d@news.astraweb.com> <db181305-97fe-4385-bf11-5323d4bd1160@googlegroups.com> <87iorzf4ro.fsf@elektro.pacujo.net> <mailman.7479.1393613988.18130.python-list@python.org> <877g8ff3hn.fsf@elektro.pacujo.net> <d5984405-9ad5-4514-98cf-1914a1de7bc8@googlegroups.com> <87wqgfdk6a.fsf@elektro.pacujo.net> <0b414429-74ee-45dd-9465-c87e98c362f2@googlegroups.com> <mailman.7485.1393634419.18130.python-list@python.org> <4bd11eec-395a-4484-a991-9fabf12328e1@googlegroups.com> <mailman.7495.1393639309.18130.python-list@python.org> <2633c4d3-e8cc-47fa-b22a-48dab2ef1a29@googlegroups.com>
Date: Sat, 1 Mar 2014 17:24:15 +1100
Subject: Re: Can global variable be passed into Python function?
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.7502.1393655058.18130.python-list@python.org>
Lines: 89
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:67297

On Sat, Mar 1, 2014 at 4:30 PM, Mark H. Harris <harrismh777@gmail.com> wrot=
e:
> hi Chris,   yeah... well think again of the switch block in C...   the sw=
itch block selects a branch based on an integral number (int character) tha=
t is generally a return code from a function.  The function hides all of th=
at logic. The function runs and returns a "number" which is passed to the s=
witch block. That number generally corresponds to a DEFINE constant at the =
top or in the header...   so we get something really readable:
>
> x =3D somefunc()
> switch (x):
>   case: CONSTANT1
>        call blah blah
>   case: CONSTANT2
>        call blah blah blah
>   default
>        blah

Okay. So you'd do that to make this more readable. Here's the original:

    if (n**2 < D(1)):
        a =3D __atan__(n)
    elif (n =3D=3D D(1)):
        a =3D gpi/4
    elif (n =3D=3D D(-1)):
        a =3D -(gpi/4)
    elif (n < D(-1)):
        a =3D __atan__Lt_neg1__(n)
    else:
        a =3D __atan__Gt_1__(n)

Now let's see. Your code doesn't perfectly translate, so I'm having to
guess a bit here.

GT_1 =3D object()
LT_n1 =3D object()
IS_1 =3D object()
IS_n1 =3D object()
def categorize(n):
    if (n**2 < D(1)):
        return None
    elif (n =3D=3D D(1)):
        return IS_1
    elif (n =3D=3D D(-1)):
        return IS_n1
    elif (n < D(-1)):
        return LT_n1
    else:
        return GT_1


   switch categorize(x):
      case GT_1:
          __atan__Gt_1__(x)
# Not sure which you mean, this
      case LT_n1:
         __atan__Lt_neg1__(x)
# or this
      case LT_1:
         __atan__Lt_1__(x)
# So I have both, ish.
      case IS_1:
         a =3D gpi/4
      case IS_n1:
         a =3D -gpi/4
      default:
# Presumably this should be a=3D?
         __atan__(x)


Please copy and paste this, and then edit it so the two actually do
exactly the same thing. And then, if you please [1], explain to me how
the second one is more readable.  It still has the exact same if/elif
tree, because there's no other way to figure out which constant you
should have for the switch; and as well as that, it exhibits an
appalling degree of Soft Coding[2], and it's roughly three times as
much code. If you want to change anything, you potentially have to
edit three places: the list of constants at the top, the condition
function, and the switch.

This can't be your idea of readability. Show me where I'm wrong.

ChrisA

[1] Steven D'Aprano unwittingly quoted HMS Pinafore a few posts back.
I'm now doing it consciously, for I hold that (on the seas) the
expression "if you please" a particularly gentlemanly tone implants.

[2] http://thedailywtf.com/Articles/Soft_Coding.aspx