[Python-Dev] Integer division transition

[Peter Funk]

Hi,

[Guido]:
> David Scherer proposed to spell this pragma as a "magical import"
> (http://www.python.org/pipermail/idle-dev/2000-April/000138.html). 

Huh?  AFAIR David Scherer and Bruce Sherwood used the 'global'-statement 
at module level as a backward compatible method to introduce module level
pragmas.  (http://www.python.org/pipermail/idle-dev/2000-April/000140.html)
I still like David Scherers proposal very much.

[David]:
> I actually implemented 1/2==0.5 in Python 1.5.2, complete with a
> module-level backward compatibility flag.  The flag made an unusual use of
> the "global" statement, which appears to be accepted at toplevel by 1.5.2
> without any effect.  Therefore a statement like "global olddivision" will be
> silently ignored by 1.5.2 and earlier, and will result in the old behavior
> under my patch.  "global" even has the right sort of sound for module-level
> options :)
> 
> An outline of what I did:
> 
> 1.  Add new opcode BINARY_FRACTION to opcode.h and dis.py
> 2.  Add new flag "int c_olddivision" to struct compiling in compile.c
> 3.  Set c_olddivision to base->c_olddivision or 0 in jcompile
> 4.  Check for "global olddivision" outside a function definition in
> com_global_stmt, and set c_olddivision=1
> 5.  Check c_olddivision in com_term, and generate either BINARY_DIVISION or
> BINARY_FRACTION
> 6.  Add PyNumber_Fraction to abstract.h, and define it in abstract.c to
> explicitly check for a pair of integers and do float division
> 7.  Add a BINARY_FRACTION case to ceval.c, which calls PyNumber_Fraction
> instead of PyNumber_Divide.

BTW:  I think the "symbol" '//' is incredible ugly and starting with
IBMs JCL years ago all languages I encountered, that used this symbol
for something, did suck in some way or another.  I would appreaciate
very much, if it could be avoided alltogether to add a symbol '//'
to Python.  '//' will look like a comment delimiter to most people today.

Using a new keyword like 'div' in the tradition of languages like 
Modula-2 looks far more attractive to me.

Regards, Peter
-- 
Peter Funk, Oldenburger Str.86, D-27777 Ganderkesee, Germany, Fax:+49 4222950260
office: +49 421 20419-0 (ArtCom GmbH, Grazer Str.8, D-28359 Bremen)