date:20130520

Re: mutable ints: I think I have painted myself into a corner

2013-05-20 Thread Cameron Simpson

On 19May2013 09:01, Peter Otten __pete...@web.de wrote:
| Cameron Simpson wrote:
| 
|  TL;DR: I think I want to modify an int value in place.
|  
|  Yesterday I was thinking about various flag set objects I have
|  floating around which are essentially bare objects whose attributes
|  I access, for example:
|  
|flags = object()
|flags.this = True
|flags.that = False
|  
|  and then elsewhere:
|  
|if flags.that:
|  do that ...
|  
|  Nice and readable, but I thought to myself: so bulky!
| 
| Plus, it doesn't work:

Yeah, sorry. My old code was a trite subclass of object.
The new broken code is a subclass of int.

|  But setting up a flags object? What I _want_ to write is code like this:
|  
|Flags = BitMask('this', 'that')
|  
|# set default state
|flags = Flags()
|flags.this = False
|flags.that = True
|... iterate over some options ...: flags.this = True
|  
|  and there's my problem. This would modify the int in place. There's
|  no way to do that. For the base type (int) this makes perfect sense,
|  as they're immutable.
|  
|  Before I toss this approach and retreat to my former object
|  technique, does anyone see a way forward to modify an int subclass
|  instance in place? (That doesn't break math, preferably; I don't
|  do arithmetic with these things but they are, after all, ints...)
| 
| No, but you could make
| 
| flags = Flags(this=False, that=True)

Yes, that is true. Flags would need to be a factory function computing
the corresponding bitmask value and then returning my new int, but
it would work. It still wouldn't let me go the whole way of modifying
the flags after instantiation.

Cheers,
-- 
Cameron Simpson c...@zip.com.au

Carpe Daemon - Seize the Background Process
- Paul Tomblin ab...@freenet2.carleton.ca
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Re: mutable ints: I think I have painted myself into a corner

2013-05-20 Thread Cameron Simpson

On 20May2013 13:23, Greg Ewing greg.ew...@canterbury.ac.nz wrote:
| Cameron Simpson wrote:
| It's an int _subclass_ so that it is no bigger than an int.
| 
| If you use __slots__ to eliminate the overhead of an
| instance dict, you'll get an object consisting of a
| header plus one reference, which is probably about the
| size of an int. But you'll also need an int to put in
| that slot, so the total size will be about twice that
| of an int.

Yeah, I was thinking I'd need to go that way. Thanks for the
suggestion.

| Another approach would be to subclass array.array and
| give instances of it type integer and size 1. Together
| with empty __slots__, it will probably be a bit bigger
| than an int, but it might still be smaller than a
| custom object plus an int.

Really? Interesting. I thinik it crosses my too baroque threshold,
but maybe not:-)

| If all of these are still too big, you might need to
| find some way of packing multiple instances into a
| single array.array.

Space isn't that real an issue at present; I'll keep that kind of
approach in mind if it comes up. This really came up because I was
feeling that the obvious object-with-boolean-attributes was terrbily
wasteful for something that can be inplemented with a single int,
in principle.

Cheers,
-- 
Cameron Simpson c...@zip.com.au

How do you blip the throttle and wave? Do you blip it real high, then wave
before the revs drop back?
Blip = right hand; Wave = left hand.  Do both simultaneously.  QED.
Doesnt this make the bike lurch forward thru the intersection?
Not if the disk lock is in place...
- Dean Woodward de...@agora.rdrop.com
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Re: Please help with Threading

2013-05-20 Thread Fábio Santos

On 18 May 2013 20:33, Dennis Lee Bieber wlfr...@ix.netcom.com wrote:
 Python threads work fine if the threads either rely on intelligent
 DLLs for number crunching (instead of doing nested Python loops to
 process a numeric array you pass it to something like NumPy which
 releases the GIL while crunching a copy of the array) or they do lots of
 I/O and have to wait for I/O devices (while one thread is waiting for
 the write/read operation to complete, another thread can do some number
 crunching).

Has nobody thought of a context manager to allow a part of your code to
free up the GIL? I think the GIL is not inherently bad, but if it poses a
problem at times, there should be a way to get it out of your... Way.
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Re: Future standard GUI library

2013-05-20 Thread Terry Jan Reedy


On 5/20/2013 1:04 AM, Vito De Tullio wrote:

Terry Jan Reedy wrote:


Do you think tkinter is going to be the standard python built-in gui
solution as long as python exists?


AT the moment, there is nothing really comparable that is a realistic
candidate to replace tkinter.


FLTK? (http://www.fltk.org/index.php)


tkinter is the Python wrapper of the tk library, just as wxpython is the 
python wrapper of the wx library. I do not see a py-fltk wrapper.



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Question about ast.literal_eval

2013-05-20 Thread Frank Millman


Hi all

I am trying to emulate a SQL check constraint in Python. Quoting from 
the PostgreSQL docs, A check constraint is the most generic constraint 
type. It allows you to specify that the value in a certain column must 
satisfy a Boolean (truth-value) expression.


The problem is that I want to store the constraint as a string, and I 
was hoping to use ast.literal_eval to evaluate it, but it does not work.


 x = 'abc'
 x in ('abc', xyz')
True
 b = x in ('abc', 'xyz')
 eval(b)
True
 from ast import literal_eval
 literal_eval(b)
ValueError: malformed node or string: _ast.Compare object at ...

Is there a safe way to do what I want? I am using python 3.3.

Thanks

Frank Millman

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CFP: MuCoCoS Workshop at PACT-2013 (Edinburgh, Scotland, UK)

2013-05-20 Thread SP

  CALL FOR PAPERS:

6th International Workshop on Multi/many-Core Computing Systems
   (MuCoCoS-2013)

  September 7, 2013, Edinburgh, Scotland, UK

   in conjunction with the 22nd Int. Conference on
  Parallel Architectures and Compilation Techniques (PACT-2013)

http://www.ida.liu.se/conferences/mucocos2013


AIMS AND SCOPE

The pervasiveness of homogeneous and heterogeneous multi-core and
many-core processors, in a large spectrum of systems from embedded and
general-purpose to high-end computing systems, poses major challenges
to software industry. In general, there is no guarantee that software
developed for a particular architecture will be executable (that is functional)
on another architecture. Furthermore, ensuring that the software preserves
some aspects of performance behavior (such as temporal or energy efficiency)
across different such architectures is an open research issue.

Therefore, this workshop focuses on language level, system software and
architectural solutions for performance portability
across different architectures and for automated performance tuning.

The topics of the MuCoCoS workshop include but are not limited to:

 * Performance measurement, modeling, analysis and tuning
 * Portable programming models, languages and compilation techniques
 * Run-time systems and hardware support mechanisms for auto-tuning
 * Tunable algorithms and data structures
 * Case studies highlighting performance portability and tuning.

As the sixth workshop in the series MuCoCoS 2008 (Barcelona, Spain),
MuCoCoS 2009 (Fukuoka, Japan), MuCoCoS 2010 (Krakow, Poland),
MuCoCoS 2011 (Seoul, Korea), and MuCoCoS 2012 (Salt Lake City, USA),
MuCoCoS 2013 will be held in Edinburgh, UK,
in conjunction with the 22nd International Conference on
Parallel Architectures and Compilation Techniques (PACT 2013).


SUBMISSION GUIDELINES

The papers should be prepared using the IEEE format
(two-column, 10pt, LaTeX users please use style IEEEtran.cls),
and no longer than 10 pages. Submitted papers will be carefully
evaluated based on originality, significance to workshop topics,
technical soundness, and presentation quality.

Please submit your paper (as PDF, viewable by Adobe Reader v5.0
or higher, with all fonts embedded please) electronically using
the online submission system
https://www.easychair.org/conferences/?conf=mucocos2013

Submission of the paper implies that, should the paper be accepted,
at least one of the authors will register and present the paper at
the workshop.

Accepted papers will be published in electronic form in
IEEE Xplore (confirmation pending).
They will also be included in the PACT USB proceedings.
We also plan to invite authors of the best MuCoCoS papers after
the workshop to submit their extended workshop papers to a special
issue of Computing Journal (Springer) (confirmation pending).


IMPORTANT DATES

Submission:   May 27, 2013 (Firm Deadline)
Notification: June 23, 2013
Camera-ready: July 7, 2013
Workshop: September 7, 2013


WORKSHOP ORGANIZATION

Christoph Kessler, Linköping University, Sweden, program chair
Sabri Pllana, Linnaeus University, Sweden, co-chair


PROGRAM COMMITTEE

Marco Aldinucci, Univ. of Torino, Italy
Beverly Bachmayer, Intel, Germany
David Bader, Georgia Tech, USA
Jacob Barhen, Oak Ridge National Lab, USA
Siegfried Benkner, Univ. of Vienna, Austria
Franz Franchetti, Carnegie Mellon University, USA
Grigori Fursin, INRIA, France
Jörg Keller, FernUniv. Hagen, Germany
Lasse Natvig, NTNU Trondheim, Norway
Mitsuhisa Sato, Univ. of Tsukuba, Japan
Samuel Thibault, INRIA / Univ. of Bordeaux, France
Philippas Tsigas, Chalmers University, Sweden
Jakub Yaghob, Charles University Prague, Czech Republic


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RE: Question about ast.literal_eval

2013-05-20 Thread Carlos Nepomuceno

It seems to me you can't use ast.literal_eval()[1] to evaluate that kind of 
expression because it's just for literals[2].

Why don't you use eval()?


[1] http://docs.python.org/2/library/ast.html#ast-helpers

[2] http://docs.python.org/2/reference/lexical_analysis.html#literals


 To: python-list@python.org
 From: fr...@chagford.com
 Subject: Question about ast.literal_eval
 Date: Mon, 20 May 2013 09:05:48 +0200

 Hi all

 I am trying to emulate a SQL check constraint in Python. Quoting from
 the PostgreSQL docs, A check constraint is the most generic constraint
 type. It allows you to specify that the value in a certain column must
 satisfy a Boolean (truth-value) expression.

 The problem is that I want to store the constraint as a string, and I
 was hoping to use ast.literal_eval to evaluate it, but it does not work.

 x = 'abc'
 x in ('abc', xyz')
 True
 b = x in ('abc', 'xyz')
 eval(b)
 True
 from ast import literal_eval
 literal_eval(b)
 ValueError: malformed node or string: _ast.Compare object at ...

 Is there a safe way to do what I want? I am using python 3.3.

 Thanks

 Frank Millman

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Re: Question about ast.literal_eval

2013-05-20 Thread Chris Angelico

On Mon, May 20, 2013 at 5:05 PM, Frank Millman fr...@chagford.com wrote:
 Hi all

 I am trying to emulate a SQL check constraint in Python. Quoting from the
 PostgreSQL docs, A check constraint is the most generic constraint type. It
 allows you to specify that the value in a certain column must satisfy a
 Boolean (truth-value) expression.

 The problem is that I want to store the constraint as a string, and I was
 hoping to use ast.literal_eval to evaluate it, but it does not work.

 x = 'abc'
 x in ('abc', xyz')
 True
 b = x in ('abc', 'xyz')
 eval(b)
 True
 from ast import literal_eval
 literal_eval(b)
 ValueError: malformed node or string: _ast.Compare object at ...

 Is there a safe way to do what I want? I am using python 3.3.

An SQL constraint has a whole lot that Python can't do conveniently,
and vice versa, so I think you do yourself a disservice by trying to
tie yourself to that.

The problem here is that 'in' is an operator, so this is not a
literal. One possible solution would be to separate out your operator
(and have just a handful permitted), and then use ast.literal_eval for
just the second operand - something like this:

import ast
import operator
ops = {
  'in':lambda x,y: x in y,  # operator.contains has the args backwards
  '==':operator.eq, # or use '=' for more SQL-like syntax
  '':operator.lt,
  '':operator.gt,
}

op, value = 'in', ('abc', 'xyz')
x = 'abc'

if ops[op](x,ast.literal_eval(value)):
  print(Constraint passed)
else:
  print(Ignore this one)

ChrisA
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Re: How to run a python script twice randomly in a day?

2013-05-20 Thread Cameron Simpson

On 20May2013 09:47, Avnesh Shakya avnesh.n...@gmail.com wrote:
| On Mon, May 20, 2013 at 9:42 AM, Cameron Simpson c...@zip.com.au wrote:
|  On 19May2013 20:54, Avnesh Shakya avnesh.n...@gmail.com wrote:
|  |How to run a python script twice randomly in a day? Actually
|  | I want to run my script randomly in a day and twice only. Please
|  | help me.. how is it possible.
| 
|  Do you mean run twice a day, each at random times?
| 
|  If so, do the obvious: at midnight, pick two random times. Sleep
|  until the first time, run the script, sleep until the second time,
|  run the script.
| 
|  There are various ways to do the sleeping and midnight bits; they're
|  up to you.
|
| Thanks, Can you mail documentation or link for it? I am totally new for it.

1: Please reply on-list; you asked the list, the discussion should
   remain there. I have added the list to the CC line.

2: Please don't top-post. Quote only the relevant bits of the
   previous message and reply below. If the message is long, do
   that in pieces. [quote] reply [quote] reply. Like a conversation.

Now, to your questions.

A UNIX user would use cron to schedule the midnight job and from
the midnight job then probably use at to schedule the other jobs
to run at specific times. See man 1 crontab, man 5 crontab to
submit the cron jobs and man at to submit the once off jobs.

UNIX means Linux, Solaris, AIX, any of the BSDs (includes MacOSX),
etc.

You could a small python script for the midnight job, and it would
submit the at jobs. See the random module to compute a pseudorandom
number (and thus a random time), the datetime module to compute
the dates and times from that number, and the subprocess module
to submit the at job for the chosen run times. The modules are
here:

  http://docs.python.org/3/py-modindex.html

That presumes python 3; if you're using python 2 the docs for that
are available at the same web site.

You don't need to use at. Your midnight job could just compute
the time in seconds to each job time, then use the time.sleep
function to delay until then. See the time module at the above
link.

Nobody on this list will write your program for you.

Attempt to write the program, then come to the list with your attempt
and any problems. People will help if you've made an initial effort,
and continue to try. This question has the feel of a homework
question; the point of homework is for you to learn by solving a
problem yourself. It is fine to seek help, but you must make the
effort yourself.

Come back with specific questions.

Cheers,
--
Cameron Simpson c...@zip.com.au

I'm not weird; I'm gifted.
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Re: Please help with Threading

2013-05-20 Thread Cameron Simpson

On 20May2013 07:25, Fábio Santos fabiosantos...@gmail.com wrote:
| On 18 May 2013 20:33, Dennis Lee Bieber wlfr...@ix.netcom.com wrote:
|  Python threads work fine if the threads either rely on intelligent
|  DLLs for number crunching (instead of doing nested Python loops to
|  process a numeric array you pass it to something like NumPy which
|  releases the GIL while crunching a copy of the array) or they do lots of
|  I/O and have to wait for I/O devices (while one thread is waiting for
|  the write/read operation to complete, another thread can do some number
|  crunching).
| 
| Has nobody thought of a context manager to allow a part of your code to
| free up the GIL? I think the GIL is not inherently bad, but if it poses a
| problem at times, there should be a way to get it out of your... Way.

The GIL makes individual python operations thread safe by never
running two at once. This makes the implementation of the operations
simpler, faster and safer. It is probably totally infeasible to
write meaningful python code inside your suggested context
manager that didn't rely on the GIL; if the GIL were not held the
code would be unsafe.

It is easy for a C extension to release the GIL, and then to do
meaningful work until it needs to return to python land. Most C
extensions will do that around non-trivial sections, and anything
that may stall in the OS.

So your use case for the context manager doesn't fit well.
-- 
Cameron Simpson c...@zip.com.au

Gentle suggestions being those which are written on rocks of less than 5lbs.
- Tracy Nelson in comp.lang.c
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RE: Please help with Threading

2013-05-20 Thread Carlos Nepomuceno

Date: Sun, 19 May 2013 13:10:36 +1000
From: c...@zip.com.au
To: carlosnepomuc...@outlook.com
CC: python-list@python.org
Subject: Re: Please help with Threading

On 19May2013 03:02, Carlos Nepomuceno carlosnepomuc...@outlook.com wrote:
| Just been told that GIL doesn't make things slower, but as I
| didn't know that such a thing even existed I went out looking for
| more info and found that document:
| http://www.dabeaz.com/python/UnderstandingGIL.pdf
|
| Is it current? I didn't know Python threads aren't preemptive.
| Seems to be something really old considering the state of the art
| on parallel execution on multi-cores.
| What's the catch on making Python threads preemptive? Are there any ongoing
projects to make that?

Depends what you mean by preemptive. If you have multiple CPU bound
pure Python threads they will all get CPU time without any of them
explicitly yeilding control. But thread switching happens between
python instructions, mediated by the interpreter.

I meant operating system preemptive. I've just checked and Python does not
start Windows threads.

The standard answers for using multiple cores is to either run
multiple processes (either explicitly spawning other executables,
or spawning child python processes using the multiprocessing module),
or to use (as suggested) libraries that can do the compute intensive
bits themselves, releasing the while doing so so that the Python
interpreter can run other bits of your python code.

I've just discovered the multiprocessing module[1] and will make some tests
with it later. Are there any other modules for that purpose?

I've found the following articles about Python threads. Any suggestions?

http://www.ibm.com/developerworks/aix/library/au-threadingpython/
http://pymotw.com/2/threading/index.html
http://www.laurentluce.com/posts/python-threads-synchronization-locks-rlocks-semaphores-conditions-events-and-queues/

[1] http://docs.python.org/2/library/multiprocessing.html

Plenty of OS system calls (and calls to other libraries from the
interpreter) release the GIL during the call. Other python threads
can run during that window.

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