Mailman 3 এপ্রিল 2000 - Python-list

TopSort in Python?
by Tim Peters 21 জানুয়ারি, 2008

21 জানুয়ারি, 2008

From: "Tim Peters" <tim_one(a)email.msn.com> [Dinu C. Gherman] > Does anybody have a simple-minded-but-working full-Python > implementation of topsort, the topological sorting algorithm? > Or maybe *any* topsort? I remember only one such algorithm... > python.org/search doesn't reveal any... Searching for "topological" instead turns up two hits there, a few more on DejaNews. Apparently "the std" algorithm I posted years ago predates DejaNews, though. So here's a fancier version ... check-out-aaron's-kjbuckets-too-ly y'rs - tim # topsort takes a list of pairs, where each pair (x, y) is taken to # mean that x <= y wrt some abstract partial ordering. The return # value is a list, representing a total ordering that respects all # the input constraints. # E.g., # topsort( [(1,2), (3,3)] ) # may return any of (but nothing other than) # [3, 1, 2] # [1, 3, 2] # [1, 2, 3] # because those are the permutations of the input elements that # respect the "1 precedes 2" and "3 precedes 3" input constraints. # Note that a constraint of the form (x, x) is really just a trick # to make sure x appears *somewhere* in the output list. # # If there's a cycle in the constraints, say # topsort( [(1,2), (2,1)] ) # then CycleError is raised, and the exception object supports # many methods to help analyze and break the cycles. This requires # a good deal more code than topsort itself! from exceptions import Exception class CycleError(Exception): def __init__(self, sofar, numpreds, succs): Exception.__init__(self, "cycle in constraints", sofar, numpreds, succs) self.preds = None # return as much of the total ordering as topsort was able to # find before it hit a cycle def get_partial(self): return self[1] # return remaining elt -> count of predecessors map def get_pred_counts(self): return self[2] # return remaining elt -> list of successors map def get_succs(self): return self[3] # return remaining elements (== those that don't appear in # get_partial()) def get_elements(self): return self.get_pred_counts().keys() # Return a list of pairs representing the full state of what's # remaining (if you pass this list back to topsort, it will raise # CycleError again, and if you invoke get_pairlist on *that* # exception object, the result will be isomorphic to *this* # invocation of get_pairlist). # The idea is that you can use pick_a_cycle to find a cycle, # through some means or another pick an (x,y) pair in the cycle # you no longer want to respect, then remove that pair from the # output of get_pairlist and try topsort again. def get_pairlist(self): succs = self.get_succs() answer = [] for x in self.get_elements(): if succs.has_key(x): for y in succs[x]: answer.append( (x, y) ) else: # make sure x appears in topsort's output! answer.append( (x, x) ) return answer # return remaining elt -> list of predecessors map def get_preds(self): if self.preds is not None: return self.preds self.preds = preds = {} remaining_elts = self.get_elements() for x in remaining_elts: preds[x] = [] succs = self.get_succs() for x in remaining_elts: if succs.has_key(x): for y in succs[x]: preds[y].append(x) if __debug__: for x in remaining_elts: assert len(preds[x]) > 0 return preds # return a cycle [x, ..., x] at random def pick_a_cycle(self): remaining_elts = self.get_elements() # We know that everything in remaining_elts has a predecessor, # but don't know that everything in it has a successor. So # crawling forward over succs may hit a dead end. Instead we # crawl backward over the preds until we hit a duplicate, then # reverse the path. preds = self.get_preds() from random import choice x = choice(remaining_elts) answer = [] index = {} in_answer = index.has_key while not in_answer(x): index[x] = len(answer) # index of x in answer answer.append(x) x = choice(preds[x]) answer.append(x) answer = answer[index[x]:] answer.reverse() return answer def topsort(pairlist): numpreds = {} # elt -> # of predecessors successors = {} # elt -> list of successors for first, second in pairlist: # make sure every elt is a key in numpreds if not numpreds.has_key(first): numpreds[first] = 0 if not numpreds.has_key(second): numpreds[second] = 0 # if they're the same, there's no real dependence if first == second: continue # since first < second, second gains a pred ... numpreds[second] = numpreds[second] + 1 # ... and first gains a succ if successors.has_key(first): successors[first].append(second) else: successors[first] = [second] # suck up everything without a predecessor answer = filter(lambda x, numpreds=numpreds: numpreds[x] == 0, numpreds.keys()) # for everything in answer, knock down the pred count on # its successors; note that answer grows *in* the loop for x in answer: assert numpreds[x] == 0 del numpreds[x] if successors.has_key(x): for y in successors[x]: numpreds[y] = numpreds[y] - 1 if numpreds[y] == 0: answer.append(y) # following "del" isn't needed; just makes # CycleError details easier to grasp del successors[x] if numpreds: # everything in numpreds has at least one predecessor -> # there's a cycle if __debug__: for x in numpreds.keys(): assert numpreds[x] > 0 raise CycleError(answer, numpreds, successors) return answer

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Blank ASP pages
by python 10 ডিসেম্বর, 2004

10 ডিসেম্বর, 2004

My server is spitting out blank .asp pages which use python. If Python is not declared, the asp pages work fine. I just yesterday stepped up to Python 1.52 and the new win32all After the install, the blanks started appearing. All the paths look fine in registry. Any clues? ( Intel dual PIII 550 Xeon, 1G RAM, NT 4.0 SP 6a, IIS 4) ************************************************** Jason S. Nadler Lead Programmer Channel21 Productions, Inc. ... What are you doing right now? **************************************************

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Dealing with faults matters (was: Is Python dying?)
by claird＠Starbase.NeoSoft.COM 28 আগস্ট, 2003

28 আগস্ট, 2003

In article <3706f449.12085377(a)news.cybercity.dk>, Morten Christensen <mmc(a)vip.cybercity.dk> wrote: >On 31 Mar 1999 06:01:03 -0600, claird(a)Starbase.NeoSoft.COM (Cameron >Laird) wrote: >>*I* certainly discuss it. Anyone who understands >>that exception-handling is important I invite to >>realize that exception-handling on the sociologi- >>cal-organizational dimension has an even bigger >>multiplier. >> >>This is a plank of my "Visual C considered profes- >>sional malpractice" campaign. > >??? > >...I understand exception handling and regard it as very important, >although the (Visual) C++ implementation is really awful (as everyone >who have experienced "unexplainable" Visual C++ exceptions of unknown >origin and type knows ).... I also know a lot about how exception >handling is actually implemented in modern OO languages such as C++ >(this was the subject I wrote my master thesis on).... > >HOWEVER, I have NO clue about what you mean by exception-handling as a >multiplier on the sociological-organization dimension :-) I would like >to find out. Can you explain? . . . Happily. Excuse my giddiness, please; I see that that last message *did* wander too far into the land of obscurity. Here's what I was saying: exception-handling is important. Programs that intelligently use exception-handling mechanisms are better programs. Exception-handling is even more important to people. People and organizations that deal with exceptions intelligently, and don't pre- tend that everything should be without fault, are better people and organizations. In fact, a correct computer program often has over half its lines devoted to accomo- dating error. A wise person will have good ways to respond to criticism/problems/diffi- culties/...; dealing with success is relatively easier. -- Cameron Laird http://starbase.neosoft.com/~claird/home.html claird(a)NeoSoft.com +1 281 996 8546 FAX

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Bug in v1.5.2 Websucker GUI?
by dhfx＠realtime.net 13 জুন, 2003

13 জুন, 2003

I'm running v1.5.2 on a Win95 box. I tried wsgui.py and got the following error message: ... File "C:\ ... \WSGUI.PY", line 165, in go self.sucker.rootdir = os.path.dirname( [ websucker.Sucker.savefilename(self.url)) ] TypeError: unbound method must be called with class instance 1st arg (the part in [ ] didn't appear in the message - I added it from the code) The object-instance self.sucker is an instantiation of class SuckerThread, which is derived from class Sucker of the websucker code module. The SuckerThread class includes a method savefilename() which overwrites the method in websucker.Sucker of the same name. Whoever coded wsgui evidently wanted to use the method of the parent class, rather than the method of the derived class. What seems to be giving trouble is that the arg of dirname() is a class method, rather than a method of an instance of the class. Here's what I did: I defined a new method savefilename1() in SuckerThread which just calls the savefilename() of the parent class: def savefilename1(self, url): return websucker.Sucker.savefilename(self, url) Then I changed the code at "line 165" to the following: self.sucker.rootdir = os.path.dirname( self.sucker.savefilename1(url)) and now it works. Note that the arg "self" of savefilename1() in the line above is not needed, it's implicit. In fact, when I had it in, I got an error message that I had too many args! David Friedman

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Re: automatic "lotjes trekken"
by François Pinard 26 আগস্ট, 2002

26 আগস্ট, 2002

"Tim Peters" <tim_one(a)email.msn.com> writes: > [...] with a belly full of far too much turkey. Strange. I was imagining you rather slim. Are you? :-) > where p[:] ranges over all permutations of range(N) [...] By the way, I do not remember any standard library helper to enumerate all permutations (or combinations, or arrangements) of a given list (or tuple). Ideally one at a time, of course. Would this be useful? -- François Pinard http://www.iro.umontreal.ca/~pinard

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Circular references and python
by Jason Stokes 27 জানুয়ারি, 2002

27 জানুয়ারি, 2002

Well, my adventures with the Python language are moving along. One thing that worries me is the lack of garbage collection in Python; the application I'm thinking of using Python for demands many data structures that use circular references, but Python only implements a reference counting scheme in the way of memory management. How do I use such data structures in Python?

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New Python Books
by python＠commandprompt.com 3 নভেম্বর, 2001

3 নভেম্বর, 2001

Hello, I recently posted this message to comp.os.python: Hello, I represent LinuxPorts.Com (http://www.linuxports.com/) and I have been approached by a printer to possibly publish OpenSource books. To start these books would just be paper versions of the actual documentation. In this case, the Python Documentation and we were wondering if this would be of interest to the Python Community. I spoke with the printer and we both have agreed that if we do this that we will be providing a portion of the Gross Profits back to the individual projects. In this case the Python project. Anyway, if this of interest to you please go to http://www.linuxports.com/ and make your vote. It will help us determine the demand for such a book. ----- We received about 8 responses with feedback that we much appreciated and would now like to solicit some more. If the people that read this email could just think about a few of the following questions and provide some feedback we would be very thankful. We are considering publishing the current set of Python documentation as a single volume versus several volumes such as toExcel does. Would this be of interest to the Python community? One person made mention of the "Vaults of Parnassus" if we were to include a snapshot of this would this be of interest? We are also considering "paying" someone to write a book about Python. Unfortunately, unlike traditional publishers the author would not get paid until the book was done, and then it would be on the basis of per book sold. We are aware that this is not the normal way of doing things, but we are not Prentice Hall and this would be the only way "currently" that we could pull this off. Is there anyone on this list that feels confident enough in their Python skills and writing ability to be able to perform such a task? Last but definitely not least, no matter what we do, if we publish a Python book, 20% to 40% of the Gross Profits would go back to the PSA. Thanks for your time: Joshua Drake Webmaster - LinuxPorts.Com WebMaster - LinuxDoc.org

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does pythonwin support adsi`
by test 17 জানুয়ারি, 2001

17 জানুয়ারি, 2001

and were to I get examples? thanks tr

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Re: Using python with Corba
by Jon K Hellan 9 জুন, 2000

9 জুন, 2000

"Fanny Yeung" <fannyy(a)idmail.com> writes: > Hi everybody, > > I am new python and I am particular interest in use python with corba. After > some research, I find out omniOrb provide interface 'omniOrbpy'. Any one > know where I can find it ? http://www.uk.research.att.com/omniORB/omniORB.html > Also, besides omniOrb2, is there any other Corba that Python can use ? Fnorb is almost pure Python. ILU does a lot of languages. ORBit is extremely fast. > Anyone know TAO can be used in Python ? Don't think so. But a Python ORB can interoperate with TAO. Regards Jon Kåre

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A Mountain of Perl Books + Python Advocacy
by lewst 3 জুন, 2000

3 জুন, 2000

Before I launch into another question and gripe, I'd like to thank everyone who offered comments and suggestions on the advanced Python books that are out there. Now something I can't quite figure out is: why are there so many more books on Perl out there than on Python? Searching through Fatbrain.COM (which is where I order my books from), I found 68 books, 4 training manuals, and 2 eMatter documents on Perl. Compare this to Python's 13 books and 2 eMatter documents. What is it about Perl that makes it so much more popular and have such a huge grassroots swell? I personally find Perl an abomination and Python a breath of fresh air. Perl has that first mover advantage I suppose, but should that really make such a hugh difference? I'll admit that Perl is what led me to Python in the first place. After hearing about how great Perl was several years ago from the local sysadmin, I learned it and started using it for my scripting needs. If there is one thing that sums up my Perl experience, it is that it always took me too long write the programs that I needed to write. The syntax was always no unnatural for me that I could never get my head out of the reference manual, and errors were always so tough to track down. In the end was frustration albeit a working result. This frustration led me to look into Python and I'll never touch Perl again. Python was so natural for me I often found myself correctly "guessing" at the syntax as I learned it. I rewrote all my Perl scripts in one weekend and most of them worked on the first try. At this point I wondered if my brain was just different than all those Perl junkies out there. But now I really don't think so; I think it's a question of awareness. Perl is very publicized and well-known while the better language is sitting here a dark corner unnoticed. Sure there will always be some religious fanatics that won't even give Python a try, but I think Python's popularity could be vastly improved with some serious advocacy work. CNRI and/or PSA should seriously look into funding a Python "marketing" campaign of sorts. I think the result would be allot of converts and more understanding and respect for Python. With this in mind, let me include one of my favorite pro-Python quotes of all time. This is from a message to the fetchmail-announce mailing list by Eric S. Raymond <http://tuxedo.org/~esr>, the famous open-source advocate and author of many popular software programs. He is discussing "fetchmailconf" which is the Tkinter GUI for his fetchmail POP/IMAP mail client. I think it demonstrates the point I make above perfectly. "A note about fetchmailconf. It took me approximately six days to write this elaborate multi-paneled GUI -- that's counting the four days it took me to learn the implementation language in the process. This could easily have been a two-month project in C (with six weeks of that spent debugging and bugs still left). Or a week-long project in Perl, with working but ugly and unmaintainable results." "The verdict: Python is *waaaay* cool! I'm sold. It's clean, it's elegant, it's easy, and it's astonishingly powerful. I'm not going to program anything longer than one screenful of script in Perl anymore. I love Larry Wall dearly, but Guido van Rossum is the better designer -- I haven't had this much fun with a language since the glory days of LISP. Eric sez check it out." Regards. __________________________________________________ Do You Yahoo!? Talk to your friends online with Yahoo! Messenger. http://im.yahoo.com

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