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Re: Why is it impossible to create a compiler than can compile Python to machinecode like C?

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On Mar 4, 2013 3:02 PM, "CM" <cmpython@gmail.com> wrote:
>
>
> > The main issue is that python has dynamic typing.  The type of object
> > that is referenced by a particular name can vary, and there's no way
> > (in general) to know at compile time what the type of object "foo" is.
> >
> > That makes generating object code to manipulate "foo" very difficult.
>
> Could you help me understand this better?  For example, if you
> have this line in the Python program:
>
> foo = 'some text'
> bar = {'apple':'fruit'}
>
> If the interpreter can determine at runtime that foo is a string
> and bar is a dict, why can't the compiler figure that out at
> compile time?  Or is the problem that if later in the program
> you have this line:
>
> foo = 12
>
> now foo is referring to an integer object, not a string, and
> compilers can't have two names referring to two different
> types of objects?  Something like that?
>
> I in no way doubt you that this is not possible, I just don't
> understand enough about how compiling works to yet "get"
> why dynamic typing is a problem for compilers.
>
> Thanks.
> --
> http://mail.python.org/mailman/listinfo/python-list

In the case of literals, the compiler can figure out type information (and
I believe it does do some constant folding). But as soon as you let
something else get in between you and the constant, you lose all guarantees.

import random

if random.random() <0.5 :
    spam = 3
else:
    spam = "hello world"

Then you get into monkey patching and dealing with types that may not be
defined at compile time. The only way a python compiler could convert that
to x86 assembly is if generated code that would look up the type
information at runtime. You'd basically be outputting a python interpreter.

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Why is it impossible to create a compiler than can compile Python to machinecode like C? kramer65 <kramerh@gmail.com> - 2013-02-28 12:25 -0800
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Matty Sarro <msarro@gmail.com> - 2013-02-28 15:50 -0500
    Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-01 02:55 +0000
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Stefan Behnel <stefan_ml@behnel.de> - 2013-02-28 22:03 +0100
    Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-01 03:47 +0000
      Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? alex23 <wuwei23@gmail.com> - 2013-02-28 20:31 -0800
      Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Stefan Behnel <stefan_ml@behnel.de> - 2013-03-01 08:48 +0100
        Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-02 01:49 +0000
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Chris Angelico <rosuav@gmail.com> - 2013-03-01 08:10 +1100
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Stefan Behnel <stefan_ml@behnel.de> - 2013-02-28 22:17 +0100
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Dave Angel <davea@davea.name> - 2013-02-28 16:18 -0500
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Modulok <modulok@gmail.com> - 2013-02-28 14:19 -0700
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Jonas Geiregat <jonas@geiregat.org> - 2013-02-28 22:33 +0100
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Nobody <nobody@nowhere.com> - 2013-02-28 22:01 +0000
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Terry Reedy <tjreedy@udel.edu> - 2013-02-28 17:06 -0500
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-02-28 21:09 -0500
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-01 04:27 +0000
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? alex23 <wuwei23@gmail.com> - 2013-02-28 20:38 -0800
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? 88888 Dihedral <dihedral88888@googlemail.com> - 2013-02-28 22:21 -0800
  Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Grant Edwards <invalid@invalid.invalid> - 2013-03-04 16:36 +0000
    Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? CM <cmpython@gmail.com> - 2013-03-04 14:55 -0800
      Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? 88888 Dihedral <dihedral88888@googlemail.com> - 2013-03-04 15:12 -0800
      Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Terry Reedy <tjreedy@udel.edu> - 2013-03-04 19:31 -0500
      Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Chris Angelico <rosuav@gmail.com> - 2013-03-05 11:33 +1100
      Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Benjamin Kaplan <benjamin.kaplan@case.edu> - 2013-03-04 16:27 -0800
    Re: Why is it impossible to create a compiler than can compile Python to machinecode like C? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-05 01:35 +0000

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