Idiom for running compiled python scripts?

[Mark]

Hi, I'm new to python and looking for a better idiom to use for the
manner I have been organising my python scripts. I've googled all over
the place about this but found absolutely nothing.

I'm a linux/unix command line guy quite experienced in shell scripts
etc. I have a heap of command line utility scripts which I run directly.
What is the best way to create python command line scripts but exploit
the (loadonly) speed-up benefit of python compiled code?

E.g. say I have a python script "myprog.py" . I could just execute that
directly each time but that means it is "compiled" each time I run it
which is not efficient and adds to startup time. I have been creating a
complimentary script "myprog" stub which just does:

#!/usr/bin/env python
from myprog import main
if __name__ == "__main__":
main()

Of course this compiles myprog.py into myprog.pyc on first run as I am
wanting.

I have one of these stubs for all my python scripts I've created so far.
Is there not a better way? Do I have to create a separate stub each
time? I find it a bit messy to require a pair of scripts for each
utility and it also contributes some inefficiency. Given the above stub
is so boilerplate, why does python not provide a general stub/utility
mechanism for this?

[Bjoern Schliessmann]

Re: Idiom for running compiled python scripts?

Mark wrote:

E.g. say I have a python script "myprog.py" . I could just execute
that directly each time but that means it is "compiled" each time
I run it which is not efficient and adds to startup time.

Did you measure the performance hit in your case?

I have one of these stubs for all my python scripts I've created
so far. Is there not a better way? Do I have to create a separate
stub each time? I find it a bit messy to require a pair of scripts
for each utility and it also contributes some inefficiency. Given
the above stub is so boilerplate, why does python not provide a
general stub/utility mechanism for this?

I've noticed that calling the interpreter with pre-compiled pyc
files also works.

Regards,


Björn


--
BOFH excuse #68:

only available on a need to know basis

[Max Erickson]

Re: Idiom for running compiled python scripts?

Mark <markbpan@maili nator.comwrote:

....

#!/usr/bin/env python
from myprog import main
if __name__ == "__main__":
main()
>
Of course this compiles myprog.py into myprog.pyc on first run as
I am wanting.
>
I have one of these stubs for all my python scripts I've created
so far. Is there not a better way? Do I have to create a separate
stub each time? I find it a bit messy to require a pair of
scripts for each utility and it also contributes some
inefficiency. Given the above stub is so boilerplate, why does
python not provide a general stub/utility mechanism for this?

I don't know of a better way to organize things, but as an
alternative, you could have a script where you import each of the
scripts that you want compiled, python will write the compiled files
to disk when you run it(thus avoiding the need to split the other
scripts). There are also the py_compile and compileall modules, which
have facilities for generating byte code.

More here:

http://effbot.org/zone/python-compile.htm

under 'Compiling python modules to byte code'.


max

[Mark]

Re: Idiom for running compiled python scripts?

So given the lack of response it seems that there is probably no such
idiom and that I should not be concerned by the inefficiency inherent in
running .py scripts directly?

I did some time tests and sure, the speed gain is slight, but it is a
gain none the less.

[Steve Holden]

Re: Idiom for running compiled python scripts?

Mark wrote:

So given the lack of response it seems that there is probably no such
idiom and that I should not be concerned by the inefficiency inherent in
running .py scripts directly?
>
I did some time tests and sure, the speed gain is slight, but it is a
gain none the less.

Someone already told you - compile the files manually (see the compile
built-in function) and then use

python file.pyc

regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden
Recent Ramblings http://holdenweb.blogspot.com

[Steve Holden]

Re: Idiom for running compiled python scripts?

Mark wrote:

So given the lack of response it seems that there is probably no such
idiom and that I should not be concerned by the inefficiency inherent in
running .py scripts directly?
>
I did some time tests and sure, the speed gain is slight, but it is a
gain none the less.

Sorry, what you really need is the compileFile() function from the
compiler module.

regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden
Recent Ramblings http://holdenweb.blogspot.com

[Steven D'Aprano]

Re: Idiom for running compiled python scripts?

On Fri, 23 Mar 2007 01:01:15 +0000, Mark wrote:

So given the lack of response it seems that there is probably no such
idiom and that I should not be concerned by the inefficiency inherent in
running .py scripts directly?
>
I did some time tests and sure, the speed gain is slight, but it is a
gain none the less.

Since you've done these tests already, perhaps you can tell us what gain
you actually got?

Here's a test I did:

[steve@apple ~]$ time python script.py
the result is 166166000

real 0m0.555s
user 0m0.470s
sys 0m0.011s
[steve@apple ~]$ time python script.pyc
the result is 166166000

real 0m0.540s
user 0m0.456s
sys 0m0.011s


That gives me an absolute gain of 15ms which is a percentage gain of about
3%. But don't forget the time it takes you to type the extra "c" at the
end of the script, even with filename completion. The average human
reaction time is something between 200 and 270 milliseconds, so unless
you're saving at least 200ms, typing that extra "c" at the end actually
wastes time.

Of course you have to type the "c". You're not deleting the source files
away are you? *wink*



--
Steven D'Aprano

[Mark]

Re: Idiom for running compiled python scripts?

On Fri, 23 Mar 2007 14:03:12 +1100, Steven D'Aprano wrote:

Since you've done these tests already, perhaps you can tell us what gain
you actually got?

About the same as you, ~20 msecs for my small script samples.

Of course you have to type the "c". You're not deleting the source files
away are you? *wink*

Sorry, the wink is lost on me?

Of course I am not deleting the sources. In fact, I am also talking
about python scripts being called from shell scripts. I guess I'm just
surprised that the python installation does not provide a small stub
invoker, e.g:

A small script called "python_compile _and_run" in "pseudo" code:

#!/usr/bin/env python
import sys

# Following is invalid syntax unfortunately :(
from sys.argv[1].rstrip('.py') import main

sys.argv = sys.argv[1:]
if __name__ == "__main__":
main()

so I could just do a "python_compile _and_run myscript.py" and it would
do what I want, i.e. run myscript.pyc if available and valid, generate
and run it if necessary.

[Gerard Flanagan]

Re: Idiom for running compiled python scripts?

On Mar 23, 8:30 am, Mark <markb...@maili nator.comwrote:

>
Of course I am not deleting the sources. In fact, I am also talking
about python scripts being called from shell scripts.

There's a nice recipe in Python Cookbook (Martelli et al.) for this.
It involves zipping your .pyc files and adding a shell stub. Never
used it before but I'm going to need something similar in the near
future, probably with a text templating system such as Cheetah
(www.cheetahtemplate.org).

HTH

Gerard

[Steven D'Aprano]

Re: Idiom for running compiled python scripts?

On Fri, 23 Mar 2007 07:30:58 +0000, Mark wrote:

On Fri, 23 Mar 2007 14:03:12 +1100, Steven D'Aprano wrote:

>Since you've done these tests already, perhaps you can tell us what gain
>you actually got?

>
About the same as you, ~20 msecs for my small script samples.

Well, I think that pretty much answers your question about whether it is
worth pre-compiling short shell scripts: you save about 20ms in execution
time, and lose 200ms in typing time. (Maybe a bit less if you are a
fast typist and don't use auto-completion.) You do the maths.

>Of course you have to type the "c". You're not deleting the source files
>away are you? *wink*

>
Sorry, the wink is lost on me?

It is because I didn't really think you were deleting the source files.
That would be incredibly stupid. But I mentioned it just in case some
not-so-bright spark decided to argue that you could use auto-completion
without needing to type that final "c" if you deleted the source file.

Presumably now somebody is going to suggest merely *moving* the source
files into another directory, thus spending a minute or two each time they
edit a script re-arranging files in order to save twenty or thirty
milliseconds when they execute the script. Hey, if your time is so
valuable that 20ms means that much to you, go for it.

Of course I am not deleting the sources. In fact, I am also talking
about python scripts being called from shell scripts. I guess I'm just
surprised that the python installation does not provide a small stub
invoker, e.g:
>
A small script called "python_compile _and_run" in "pseudo" code:

[snip pseudo-code]

so I could just do a "python_compile _and_run myscript.py" and it would
do what I want, i.e. run myscript.pyc if available and valid, generate
and run it if necessary.

You shouldn't expect Python to come with every imaginable special-purpose
script already written for you! Besides, it's pretty simple to get that
functionality by hand when you need it, or automatically for that matter.

Here's one (untested) script that executes the pyc file in a subshell if
it exists and is new enough, and compiles it if it doesn't.


import os, sys, compiler
from stat import ST_MTIME as MT
if __name__ == "__main__":
scriptname = sys.argv[1]
compiledname = scriptname + "c"
if not os.path.exists( compiledname) or \
os.stat(compile dname)[MT] < os.stat(scriptn ame)[MT]:
# compiled file doesn't exist, or is too old
compiler.compil eFile(scriptnam e)
assert os.path.exists( compiledname)
resultcode = os.system('pyth on %s' % compiledname)
sys.exit(result code)

Now don't forget to test whether launching the subshell takes longer than
the 20ms you might save. All that effort, and wouldn't it be ironic if it
was actually *slower* than executing the script from scratch each time...


--
Steven.

[mark]

Re: Idiom for running compiled python scripts?

On Fri, 23 Mar 2007 22:24:07 +1100, Steven D'Aprano wrote:

if not os.path.exists( compiledname) or \ os.stat(compile dname)[MT] <
os.stat(scriptn ame)[MT]:
# compiled file doesn't exist, or is too old

Surely the validity check done by Python is more sophisticated than
this? Doesn't the binary file have to be compiled under the same python
version etc?

Now don't forget to test whether launching the subshell takes longer
than the 20ms you might save. All that effort, and wouldn't it be ironic
if it was actually *slower* than executing the script from scratch each
time...

But Python proper is executing all the above anyhow isn't it? So the 20
msecs advantage I measured already includes this logic.

Anyhow, I give up. Compilation, it seems, only applies to python
modules. Compilation is not appropriate for Python scripts. Should be
in the FAQ.

[Steven D'Aprano]

Re: Idiom for running compiled python scripts?

On Fri, 23 Mar 2007 12:22:44 +0000, mark wrote:

On Fri, 23 Mar 2007 22:24:07 +1100, Steven D'Aprano wrote:

> if not os.path.exists( compiledname) or \ os.stat(compile dname)[MT] <
> os.stat(scriptn ame)[MT]:
> # compiled file doesn't exist, or is too old

>
Surely the validity check done by Python is more sophisticated than
this? Doesn't the binary file have to be compiled under the same python
version etc?

Of course. What, do you want me to do all your work? :-)

>Now don't forget to test whether launching the subshell takes longer
>than the 20ms you might save. All that effort, and wouldn't it be ironic
>if it was actually *slower* than executing the script from scratch each
>time...

>
But Python proper is executing all the above anyhow isn't it? So the 20
msecs advantage I measured already includes this logic.

I don't know how you measured the 20ms.

When you call a script direct from the shell, you've already got a shell
running. When you call a script from within Python via os.system, it has
to launch a sub-shell. That takes time.

Anyhow, I give up. Compilation, it seems, only applies to python
modules. Compilation is not appropriate for Python scripts. Should be
in the FAQ.

No, that's not true. Python scripts certainly take advantage of compiled
modules.

The real lesson of this is that optimization isn't necessarily
straightforward . What we imagine "should be" faster might not be in
practice -- especially when dealing with micro-optimizations that only
save a few tens of milliseconds.

Frankly, it simply isn't worth trying to save 20ms in a script that takes
less than a second to run. If you scratch your nose before hitting enter,
you've wasted a hundred times what you've just spent hours trying to save.

Or, to put it another way:

The Rules of Optimization are simple.
Rule 1: Don't do it.
Rule 2 (for experts only): Don't do it yet.
-- Michael A. Jackson (no, not that Michael Jackson), "Principles of
Program Design", 1975.



--
Steven.

[Alex Martelli]

Re: Idiom for running compiled python scripts?

Mark <markbpan@maili nator.comwrote:
...

so I could just do a "python_compile _and_run myscript.py" and it would
do what I want, i.e. run myscript.pyc if available and valid, generate
and run it if necessary.

You can use

python -c 'import myscript; myscript.main() '

and variations thereon.


Alex

[Mark]

Re: Idiom for running compiled python scripts?

On Fri, 23 Mar 2007 07:47:04 -0700, Alex Martelli wrote:

You can use
>
python -c 'import myscript; myscript.main() '
>
and variations thereon.

Hmmm, after all that, this seems to be close to what I was looking for.

Thanks Alex. Didn't find anything about this in your cookbook! (I'm just
starting reading it whole - best way to really learn the language I
think).

So the general purpose invoking bash script e.g. "runpy" is merely something
like:

############### ############### ############### ############### #####
#!/bin/bash

if [ $# -lt 1 ]; then
echo "usage: `basename $0` script.py [script args ..]"
exit 1
fi

PROG=$1
DIR=`dirname $PROG`
MOD=`basename $PROG`
MOD=${MOD%.py}
shift
exec python -c "import sys; \
sys.argv[0] = \"$PROG\"; \
sys.path.append (\"$DIR\"); \
import $MOD; $MOD.main()" $@
############### ############### ############### ############### #####

So I timed "~/bin/myscript.py myargs" against "runpy ~/bin/myscript.py
myargs" but got only maybe a couple of millisec improvement (using a
1000 line myscript.py which just immediately exits - to try and push the
advantage!).

So I agree - the ends do not justify the means here and I'll just
execute myscript.py directly. Still not sure why python does not provide
this as a "python --compile_and_run myscript.py" option though?! ;)

[irstas@gmail.com]

Re: Idiom for running compiled python scripts?

On Mar 23, 9:30 am, Mark <markb...@maili nator.comwrote:

A small script called "python_compile _and_run" in "pseudo" code:
>
#!/usr/bin/env python
import sys
>
# Following is invalid syntax unfortunately :(
from sys.argv[1].rstrip('.py') import main
>
sys.argv = sys.argv[1:]
if __name__ == "__main__":
main()
>
so I could just do a "python_compile _and_run myscript.py" and it would
do what I want, i.e. run myscript.pyc if available and valid, generate
and run it if necessary.

There's __import__ which allows you to do what you tried:

m = __import__(sys. argv[1].rstrip('.py'))

Also, rstrip doesn't work like you think it does.
'pyxyypp.py'.rs trip('.py') == 'pyx'

Answering also to your later message:

So the general purpose invoking bash script e.g. "runpy" is merely something

like:

Curiously enough, Python 2.5 has a module called runpy:

http://docs.python.org/lib/module-runpy.html

which seems to almost do what you want. It doesn't compile the modules
but you could make a modification which does. The benefit over just
using __import__("mod ule").main() would be
that your scripts wouldn't necessarily need a function called "main",
but would still work with scripts that use the __name__ == '__main__'
idiom.
A simple implementation that "works":


import imp, sys, os
c = sys.argv[1]
if not os.path.exists( c + 'c') or os.stat(c).st_m time os.stat(c +
'c').st_mtime:
import compiler
compiler.compil eFile(c)
del sys.argv[0]
imp.load_compil ed('__main__', c + 'c')


I timed it against running plain .py and running .pyc directly.
It seemed to be roughly on par with running .pyc directly, and about
18ms
faster than running .py. The file had 600 lines (21kb) of code.