Re: Why Python is slow

From	Richard Heathfield <rjh@cpax.org.uk>
Newsgroups	comp.lang.c
Subject	Re: Why Python is slow
Date	2017-01-24 20:14 +0000
Organization	Fix this later
Message-ID	<o68cgo$js$1@dont-email.me> (permalink)
References	<9048e105-65e6-4e8c-a42f-b37e1d327246@googlegroups.com> <expression-20170124202746@ram.dialup.fu-berlin.de>

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On 24/01/17 19:45, Stefan Ram wrote:
> thunderbirdmember@gmail.com writes:
>> Python is easy to write but is slow executing things.
>
>   Just a few days ago, I wrote my first Python expression
>   and fed it to an interpreter. It was
>
> 3**3**3**3
>
>   . Ok, it was not the very first Python expression I ever
>   entered, but one of the first ten.
>
>   How long does it take to evaluate it? (I don't know, because
>   I eventually aborted the interpreter while it was still
>   evaluating this expression.)

What did you expect? :-)

3**3**3**3 is

3**3**27 is

3**7625597484987

which is going to tax the capabilities of most processors, no matter 
what language you use to write the code.

3 to the power 3 took 0.008 seconds on my system.

3 to the power 27 took 0.018 seconds.

I bottled out of the full monty, but:

3 to the power 81 took 0.029 seconds.
3 to the power 243 took 0.042 seconds.
3 to the power 729 took 0.111 seconds.
3 to the power 2187 took 0.740 seconds.
3 to the power 6561 took 6.427 seconds.
3 to the power 19683 took 56.875 seconds.

Multiplying the power term by 3, then, seems to multiply the run-time by 
about 9. So we can estimate the time it would take (machine resources 
permitting) to perform 3 to the power 7625597484987 as 56.875 * (9 to 
the power 22), which is roughly 1,774,861,793,744,000 years.

You can probably cut this time down a lot by using bigger bigits (my 
bigits are deliberately small, 0-255).

If we were to make the rather optimistic assumption that we could cut 
the time by a factor of 2^56 by using 64-bit bigits instead of 8-bit 
bigits, we could get the result in just over a Beatles week.

-- 
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within

Thread

Why Python is slow thunderbirdmember@gmail.com - 2017-01-24 10:22 -0800
  Re: Why Python is slow Richard Heathfield <rjh@cpax.org.uk> - 2017-01-24 18:33 +0000
  Re: Why Python is slow Richard Heathfield <rjh@cpax.org.uk> - 2017-01-24 20:14 +0000
    Re: Why Python is slow luser droog <luser.droog@gmail.com> - 2017-01-26 10:13 -0800
    Re: Why Python is slow Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-30 05:50 -0800
  Re: Why Python is slow bart4858@gmail.com - 2017-01-24 13:21 -0800
  Re: Why Python is slow BartC <bc@freeuk.com> - 2017-01-24 22:23 +0000
  Re: Why Python is slow "Chris M. Thomasson" <invalid@invalid.invalid> - 2017-01-24 17:11 -0800
    Re: Why Python is slow "Chris M. Thomasson" <invalid@invalid.invalid> - 2017-01-24 19:26 -0800
    Re: Why Python is slow "Chris M. Thomasson" <invalid@invalid.invalid> - 2017-01-25 12:50 -0800
      Re: Why Python is slow BartC <bc@freeuk.com> - 2017-01-25 21:52 +0000
        Re: Why Python is slow "Chris M. Thomasson" <invalid@invalid.invalid> - 2017-01-25 14:30 -0800
          Re: Why Python is slow BartC <bc@freeuk.com> - 2017-01-25 22:59 +0000
            Re: Why Python is slow "Chris M. Thomasson" <invalid@invalid.invalid> - 2017-01-27 13:20 -0800
      Re: Why Python is slow DFS <nospam@dfs.com> - 2017-01-25 19:22 -0500
        Re: Why Python is slow "Chris M. Thomasson" <invalid@invalid.invalid> - 2017-01-26 13:40 -0800
  Re: Why Python is slow David Brown <david.brown@hesbynett.no> - 2017-01-25 10:29 +0100
    Re: Why Python is slow gazelle@shell.xmission.com (Kenny McCormack) - 2017-01-25 10:38 +0000
    Re: Why Python is slow Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-26 06:44 -0800
      Re: Why Python is slow Richard Heathfield <rjh@cpax.org.uk> - 2017-01-26 15:00 +0000
        Re: Why Python is slow Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-26 17:23 +0000
          Re: Why Python is slow supercat@casperkitty.com - 2017-01-26 09:42 -0800
            Re: Why Python is slow Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-26 18:24 +0000
      Re: Why Python is slow David Brown <david.brown@hesbynett.no> - 2017-01-26 16:14 +0100
        Re: Why Python is slow Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-26 12:49 -0800
          Re: Why Python is slow Robert Wessel <robertwessel2@yahoo.com> - 2017-01-26 15:11 -0600
          Re: Why Python is slow David Brown <david.brown@hesbynett.no> - 2017-01-26 23:56 +0100
        Re: Why Python is slow Keith Thompson <kst-u@mib.org> - 2017-01-26 15:20 -0800
          Re: Why Python is slow David Brown <david.brown@hesbynett.no> - 2017-01-27 09:31 +0100
      Re: Why Python is slow fir <profesor.fir@gmail.com> - 2017-01-27 07:24 -0800
        Re: Why Python is slow fir <profesor.fir@gmail.com> - 2017-01-27 07:57 -0800
          Re: Why Python is slow fir <profesor.fir@gmail.com> - 2017-01-27 08:46 -0800
        Re: Why Python is slow supercat@casperkitty.com - 2017-01-27 08:06 -0800
          Re: Why Python is slow fir <profesor.fir@gmail.com> - 2017-01-27 08:39 -0800
            Re: Why Python is slow fir <profesor.fir@gmail.com> - 2017-01-27 13:29 -0800
  Re: 3**3**3**3 Noob <root@127.0.0.1> - 2017-01-27 14:33 +0100

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