🌐 Mailman 3 October 2008 - Python-list - python.org

Tree or hierarchical structure
by Abah Joseph Oct. 31, 2008

Oct. 31, 2008

I need tutorial or book on Tree or hierarchical structure using Python.

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Optparse object containing generators: only seem to work if given particular names?
by John O'Hagan Oct. 31, 2008

Oct. 31, 2008

Here's a strange one for you: I have a generator function which produces lists of numbers and takes options which influence the output. The generator contains a loop, and to enable the options to have a different value on each iteration, the options may themselves be instances of the same generator, in the form of attributes of an optparse object. In the body of the loop, the next() method is called on each generator to get the new value each time. This enables me to either: - pass an option either a single value as and have it yielded repeatedly by a dummy generator, - or, by using the (arbitrarily chosen) word "CTRL:" after the option, followed by another set of options - in quotes - suitable for the main generator, to pass a changing value. The problem: whether it works or not depends on what name is given to the destination in parser.values()! Strange but true. I haven't yet been able to figure out if there's any pattern to this, but names that work include: "add", "A", "rand", and "updown". Some that don't are "descend", "random", and "Z". When it doesn't work, the error is: TypeError: unsupported operand type(s) for +: 'int' and 'generator' So apparently when given one of the "wrong" names, calling options. [wrongname].next() yields another generator object, whereas with the "right" names, it yields the expected value. Below is a working "sandbox" version of the relevant part of the actual program, but with a hard-coded value for the number list and only a single option, --add, which either adds the number given next on the command line to each element of the list, or, if followed by CTRL: '' " (that's a pair of empty quotes) will sequentially do the same for each member of the list. (If the option is repeated inside the quotes, the altered list will be used to apply the addition, and so on.) If you don't believe me (and I'm finding this hard to believe myself), try some different names in the two inline-commented places (of course, both have to be the same). Some will work, others won't. I'm baffled, and hope someone here may be interested in figuring out why this is happening. Thanks, John O'Hagan Here's the code: import sys from optparse import OptionParser def my_callback(option, opt_str, value, parser): rargs = parser.rargs if rargs[0] == "CTRL:" : setattr(parser.values, option.dest+"_ctrl", rargs[1].split()) else: value = abs(int(rargs[0])) setattr(parser.values, option.dest, value) def parse(option_list): parser = OptionParser() parser.add_option("--add", action="callback", callback=my_callback, dest="add") ## The troublesome name! (options, args) = parser.parse_args(option_list) return options def numerical_ctrl(generator): for number_list in generator: for number in number_list: yield number def dummy_ctrl(value): while 1: yield value #This next bit should ideally be incorporated into the callback function above #(later!) #It converts the attributes of the "options" object to generators. def iterizer( options ): for opt in vars( options ) : if "_ctrl" in opt: ctrl_opts_list = getattr( options, opt ) setattr(options, opt, dummy_ctrl( getattr( options, opt ) ) ) opt = opt.replace( "_ctrl", "" ) ctrl_opts = parse( ctrl_opts_list ) ctrl_opts = iterizer( ctrl_opts ) generator = phrase_engine( ctrl_opts ) generator = numerical_ctrl( generator ) else: generator = dummy_ctrl( getattr( options, opt ) ) setattr (options, opt , generator) return options #The number list generator: def phrase_engine(options): counter = 0 while counter < 10: sequence = [1, 2, 3] add = options.add.next() ##Here is the troublesome name again. if add : sequence = [ i + add for i in sequence ] yield sequence counter += 1 options = parse( sys.argv[ 1: ] ) options = iterizer(options) for i in phrase_engine(options): print i

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how to run python file from the python IDLE editor
by Seid Mohammed Oct. 31, 2008

Oct. 31, 2008

Greetins all 1. I can easily run python file from a comand prompt just typing "python filname.py". How can I do this from the python IDLE shell 2. How to create EXE in python. thanks all for making me to be more copnfortable with python Seid M -- "RABI ZIDNI ILMA"

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Re: modifying locals
by Steven D'Aprano Oct. 31, 2008

Oct. 31, 2008

On Thu, 30 Oct 2008 14:21:01 -0700, John [H2O] wrote: > I would like to write a function to write variables to a file and modify > a few 'counters'. Are you talking about a function to generate Python source code? > This is to replace multiple instances of identical > code in a module I am writing. Surely the right way to do this is to factor out the identical code into a function, and then call the function. > This is my approach: > > def write_vars(D): > """ pass D=locals() to this function... """ > for key in D.keys(): > exec("%s = %s" % (key,D[key])) That would be better written as: for key,item in D.iteritems(): exec "%s = %s" % (key, item) exec is a statement, not a function, and doesn't require brackets. > outfile.write(...) > numcount += 1 > do this, do that... > > the issue is that at the end, I want to return outfile, numcount, etc... > but I would prefer to not return them explicitly, that is, I would just > like that the modified values are reflected in the script. How do I do > this? Using global? But that seems a bit dangerous since I am using > exec. What you are actually trying to do is unclear to me. Perhaps you could try explaining better with a more concrete example? I wounder whether this might be what you are after? # start of script (untested) counter = 0 # define a counter in the module scope (global) filename = 'foo.txt' def make_vars(): global outfile, numcount # force names to be in module scope outfile = open(filename, 'w') numcount = 99 try: numcount except NameError: print "numcount doesn't exist yet, making it" make_vars() print numcount # end script But of course the above can be written much more concisely as: # start of script (untested) counter = 0 filename = 'foo.txt' outfile = open(filename, 'w') numcount = 99 print numcount # end script so I'm not really sure you're trying to do what you seem to be doing. -- Steven

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[Novice]Installing eric4 with python 2.6
by Saurabh Agrawal Oct. 31, 2008

Oct. 31, 2008

Hi, I am fairly new to python. Coming from a world of IDEs, I wanted a fancier one than IDLE. Hence, I downloaded eric4. When I tried to compile it, it asked for PyQt4, which I again downloaded (exe for Windows XP) and installed it. It seems to be properly installed as I can invoke "import PyQt4" from IDLE without any complaints. However, when I try to install eric4, I am getting the following error: D:\Python26\eric4-4.2.2a>python install.py Sorry, please install PyQt4. Error: Module use of python25.dll conflicts with this version of Python. So, won't eric4 work with python 2.6? I have searched on the net for this, but am unable to find any solution. I am new to python, so please excuse if this has an obvious solution. Thanks. OS: Windows XP SP2. Regards, Saurabh.

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Malaysia python programmers
by Marcus.CM Oct. 31, 2008

Oct. 31, 2008

Hi, I apologize if this is not the place to do this. A python user group for malaysia is currently being formed , so if you are in malaysia, feel free to join us at : www.python.my Marcus.CM.

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Re: 2.6, 3.0, and truly independent intepreters
by Rhamphoryncus Oct. 31, 2008

Oct. 31, 2008

On Oct 30, 8:23 pm, "Patrick Stinson" <patrickstinson.li...(a)gmail.com> wrote: > Speaking of the big picture, is this how it normally works when > someone says "Here's some code and a problem and I'm willing to pay > for a solution?" I've never really walked that path with a project of > this complexity (I guess it's the backwards-compatibility that makes > it confusing), but is this problem just too complex so we have to keep > talking and talking on forum after forum? Afraid to fork? I know I am. > How many people are qualified to tackle Andy's problem? Are all of > them busy or uninterested? Is the current code in a tight spot where > it just can't be fixed without really jabbing that FORK in so deep > that the patch will die when your project does? > > Personally I think this problem is super-awesome on the hobbyest's fun > scale. I'd totally take the time to let my patch do the talking but I > haven't read enough of the (2.5) code. So, I resort to simply reading > the newsgroups and python code to better understand the mechanics > problem :( The scale of this issue is why so little progress gets made, yes. I intend to solve it regardless of getting paid (and have been working on various aspects for quite a while now), but as you can see from this thread it's very difficult to convince anybody that my approach is the *right* approach.

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Re: 2.6, 3.0, and truly independent intepreters
by Jesse Noller Oct. 31, 2008

Oct. 31, 2008

On Wed, Oct 29, 2008 at 8:05 PM, Glenn Linderman <v+python(a)g.nevcal.com> wrote: > On approximately 10/29/2008 3:45 PM, came the following characters from the > keyboard of Patrick Stinson: >> >> If you are dealing with "lots" of data like in video or sound editing, >> you would just keep the data in shared memory and send the reference >> over IPC to the worker process. Otherwise, if you marshal and send you >> are looking at a temporary doubling of the memory footprint of your >> app because the data will be copied, and marshaling overhead. > > Right. Sounds, and is, easy, if the data is all directly allocated by the > application. But when pieces are allocated by 3rd party libraries, that use > the C-runtime allocator directly, then it becomes more difficult to keep > everything in shared memory. > > One _could_ replace the C-runtime allocator, I suppose, but that could have > some adverse effects on other code, that doesn't need its data to be in > shared memory. So it is somewhat between a rock and a hard place. > > By avoiding shared memory, such problems are sidestepped... until you run > smack into the GIL. If you do not have shared memory: You don't need threads, ergo: You don't get penalized by the GIL. Threads are only useful when you need to have that requirement of large in-memory data structures shared and modified by a pool of workers. -jesse

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Re: Finding the instance reference of an object
by greg Oct. 31, 2008

Oct. 31, 2008

Gabriel Genellina wrote: > En Tue, 28 Oct 2008 00:58:10 -0200, greg <greg(a)cosc.canterbury.ac.nz> > escribió: > >> (1) Call by value: The actual parameter is an expression. It is >> evaluated and the result is assigned to the formal parameter. >> Subsequent assignments to the formal parameter do not affect >> the actual parameter. >> >> (2) Call by reference: The actual parameter is an lvalue. The >> formal parameter becomes an alias for the actual parameter, >> so that assigning to the formal parameter has the same >> effect as assigning to the actual parameter. > > Those definitions are only applicable to unstructured, primitive types, > where the only relevant operations are "get value" and "assign value". > Structured types provide other operations too - like selection > (attribute get/set in Python). But that isn't what "assigning to the formal parameter" means -- it only means assigning directly to the parameter *name*. > It is unspecified on both definitions > above what happens in those cases. That's true, but it's outside the scope of the parameter passing mechanism to define what happens in those cases. That's down to the data model being used by the language and the semantics of assignment in general. -- Greg

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Re: Printing with interspersed element
by Matimus Oct. 31, 2008

Oct. 31, 2008

On Oct 30, 2:10 pm, "Paulo J. Matos" <pocma...(a)gmail.com> wrote: > On Thu, Oct 30, 2008 at 8:42 PM, Arnaud Delobelle > > > > <arno...(a)googlemail.com> wrote: > > On Oct 30, 8:07 pm, "Paulo J. Matos" <p...(a)ecs.soton.ac.uk> wrote: > >> Hi all, > > >> I guess this is a recurring issue for someone who doesn't really know > >> the python lib inside out. There must be a simple way to do this. > >> I have a list of objects [x1, x2, x3, ..., xn] and I have defined a > >> print method for them print_obj(). Now I want to print them > >> intersepersed by an element. > >> If I print [x1, x2, x3] interspersed by the element 10: > >> x1.print_obj() 10 x2.print_obj() 10 x3.print_obj() > > >> Now, the question is, what's the best way to do this? > > > Defining a print_obj() method is probably a bad idea. What if you > > want to print to a file for example? Instead you can define a > > __str__() method for your objects and then use the join() method of > > strings like this: > > > print ' 10 '.join(str(x) for x in lst) > > Thanks for the tip but that has an issue when dealing with potentially > millions of objects. You are creating a string in memory to then dump > to a file [or screen] while you could dump to the file [or screen] as > you go through the original string. Right? Then I hope you are using stackless, because you are going to stack overflow _way_ before you recurse 1 million times. def print_list(seq, sep=','): seq = iter(seq) print seq.next(), for item in seq: print sep, print item, print Matt

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