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

Suggestions for creating a PDF table
by Kirk Strauser Aug. 8, 2008

Aug. 8, 2008

Short question: Is there a good library for generating HTML-style tables with the equivalent of colspans, automatically sized columns, etc. that can render directly to PDF? Longer question: I'm re-doing a big chunk of locally-written code. I have a report-generating function that takes a list of lists of lists as input and returns either a PDF, an HTML table, or an Excel spreadsheet as requested. For example, input might look like: makereport('html', headers=['Invoice number', 'Customer', 'Price'], data=[ [['123', 'John Doe', '$50.00'], ['Ordered on 2008-01-01 via the website']], [['124', 'Peter Bilt', '$25.99'], ['Mail via African swallow']] ]) This would result in HTML like: <table> <tr> <th>Invoice number</th> <th>Customer</th> <th>Price</th> </tr> <tr class="lightbackground"> <td>123</td> <td>John Doe</td> <td>$50.00</td> </tr> <tr class="lightbackground"> <td colspan="3">Ordered on 2008-01-01 via the website</td> </tr> <tr class="darkerbackground"> <td>124</td> <td>Peter Bilt</td> <td>$25.99</td> </tr> <tr class="darkerbackground"> <td colspan="3">Mail via African swallow</td> </tr> </table> Note particularly how the explanatory notes for each invoice are similar in appearance to the "primary" report lines they're associated with. Now, I have a similar transformation to PDF via pdflatex. This works fairly well but requires a bunch of temp files and subprocesses, and I've never been 100% happy with the LaTeX output (you have to calculate your own column widths, for instance). Since I plan to re-write this anyway, I'd like to find a more widely used library if one was available. ReportLab seemed *almost* perfect, except that it doesn't support colspans. As I hope I demonstrated in the example, most of our reports depend on that ability. So, again, any thoughts on a PDF generator that can generate tables with the same kind of flexibility as HTML? -- Kirk Strauser

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iterating "by twos"
by kj Aug. 7, 2008

Aug. 7, 2008

Is there a special pythonic idiom for iterating over a list (or tuple) two elements at a time? I mean, other than for i in range(0, len(a), 2): frobnicate(a[i], a[i+1]) ? I think I once saw something like for (x, y) in forgotten_expression_using(a): frobnicate(x, y) Or maybe I just dreamt it! :) Thanks! -- NOTE: In my address everything before the first period is backwards; and the last period, and everything after it, should be discarded.

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Questions about asyncore
by Frank Millman Aug. 6, 2008

Aug. 6, 2008

Hi all I have been using my own home-brewed client/server technique for a while, using socket and select. It seems to work ok. The server can handle multiple clients. It does this by creating a new thread for each connection. Each thread runs its own select loop. I am making some fairly big changes, so I thought I would look at asyncore. I modified my program to use asyncore without much trouble, and it feels nicer. It uses async I/O instead of threading, and it relieves me of having to run my own select loop. I have two questions. They both relate to whether I am using the module as intended. The documentation is rather sparse, and I know from experience that just getting something working is no guarantee that I am getting the full benefit. Firstly, having got asyncore working, I had a look at asynchat. As far as I can see I get very little benefit from using it. I have already set up a 'messaging' protocol between server and client, where all messages consist of 5 digits for the message length, followed by the message. The message consists of a pickled tuple, where the first element is a message identifier, and the rest is the message body. This is how it works in asyncore - def __init__(self,channel): [...] self.msgLength = 0 self.recvData = '' # temporary buffer def handle_read(self): self.recvData += self.recv(8192) if not self.msgLength: if len(self.recvData) < 5: # 1st 5 bytes = msg length return self.msgLength = int(self.recvData[:5]) self.recvData = self.recvData[5:] if len(self.recvData) < self.msgLength: return data = loads(self.recvData[:self.msgLength]) self.recvData = self.recvData[self.msgLength:] self.msgLength = 0 [handle data] This is how I got it working in asynchat - def __init__(self,channel): [...] self.recvData = '' # temporary buffer self.set_terminator(5) self.gotMsgLength = False def collect_incoming_data(self, data): self.recvData += data def found_terminator(self): if self.gotMsgLength: # what follows is the message data = loads(self.recvData) self.set_terminator(5) self.gotMsgLength = False [handle data] else: # what follows is the message length self.set_terminator(int(self.recvData)) self.gotMsgLength = True self.recvData = '' It may be slightly neater, but it does not seem worth adding an extra layer just for that. Does asynchat give me any other benefits I may have overlooked? My second question relates to writing a dummy client program to test the server. I just want to send it some messages and print the responses. Some messages incorporate data extracted from previous responses, so I have to wait for the reply before continuing. I am using asyncore for this as well. However, the only way I can think of to get it working is to run asyncore.dispatcher in a separate thread. To send messages, I append them to a list of messages to be sent. The dispatcher method writable() returns True if there is anything in the list, else False. To receive messages, I run a 'while 1' loop in the main thread, with a sleep of 0.1, until recvData has something in it. It works, but it seems odd to use a separate thread, as one of the points of asyncore is to avoid multi-threading. Is there a better way to write the client program? Thanks Frank Millman

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Difference between type and class
by Nikolaus Rath Aug. 5, 2008

Aug. 5, 2008

Hello, Can someone explain to me the difference between a type and a class? After reading http://www.cafepy.com/article/python_types_and_objects/ it seems to me that classes and types are actually the same thing: - both are instances of a metaclass, and the same metaclass ('type') can instantiate both classes and types. - both can be instantiated and yield an "ordinary" object - I can even inherit from a type and get a class So why does Python distinguish between e.g. the type 'int' and the class 'myclass'? Why can't I say that 'int' is a class and 'myclass' is a type? I hope I have managed to get across the point of my confusion... Thanks in advance, -Nikolaus -- »It is not worth an intelligent man's time to be in the majority. By definition, there are already enough people to do that.« -J.H. Hardy PGP fingerprint: 5B93 61F8 4EA2 E279 ABF6 02CF A9AD B7F8 AE4E 425C

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Python-URL! - weekly Python news and links (Jul 28)
by Gabriel Genellina Aug. 5, 2008

Aug. 5, 2008

QOTW: "Python's goals are to maximize opportunities for good programming, which is quite different." - Bruno Desthuilliers, contrasting Python with Java Load and initialize dynamic plugins from a directory: http://groups.google.com/group/comp.lang.python/browse_thread/thread/ba8d36… Importing different versions of a module: http://groups.google.com/group/comp.lang.python/browse_thread/thread/9039a7… Some details on the CPython VM implementation: http://groups.google.com/group/comp.lang.python/browse_thread/thread/d36bc1… "Real languages are written in C#, not decadent C" (or something like that ...): http://groups.google.com/group/comp.lang.python/browse_thread/thread/355439… The different 64bits architectures supported by different Python implementations: http://groups.google.com/group/comp.lang.python/browse_thread/thread/b8bcb7… Looking for a "scanf" replacement: http://groups.google.com/group/comp.lang.python/browse_thread/thread/26a24e… Python and tail-call optimization: http://groups.google.com/group/comp.lang.python/browse_thread/thread/25ff95… A long thread against the "Explicit is better than implicit" principle: http://groups.google.com/group/comp.lang.python/browse_thread/thread/a5fa8f… ======================================================================== Everything Python-related you want is probably one or two clicks away in these pages: Python.org's Python Language Website is the traditional center of Pythonia http://www.python.org Notice especially the master FAQ http://www.python.org/doc/FAQ.html PythonWare complements the digest you're reading with the marvelous daily python url http://www.pythonware.com/daily Mygale is a news-gathering webcrawler that specializes in (new) World-Wide Web articles related to Python. http://www.awaretek.com/nowak/mygale.html While cosmetically similar, Mygale and the Daily Python-URL are utterly different in their technologies and generally in their results. Just beginning with Python? This page is a great place to start: http://wiki.python.org/moin/BeginnersGuide/Programmers The Python Papers aims to publish "the efforts of Python enthusiats": http://pythonpapers.org/ The Python Magazine is a technical monthly devoted to Python: http://pythonmagazine.com Readers have recommended the "Planet" sites: http://planetpython.org http://planet.python.org comp.lang.python.announce announces new Python software. Be sure to scan this newsgroup weekly. http://groups.google.com/groups?oi=djq&as_ugroup=comp.lang.python.announce Python411 indexes "podcasts ... to help people learn Python ..." Updates appear more-than-weekly: http://www.awaretek.com/python/index.html The Python Package Index catalogues packages. http://www.python.org/pypi/ The somewhat older Vaults of Parnassus ambitiously collects references to all sorts of Python resources. http://www.vex.net/~x/parnassus/ Much of Python's real work takes place on Special-Interest Group mailing lists http://www.python.org/sigs/ Python Success Stories--from air-traffic control to on-line match-making--can inspire you or decision-makers to whom you're subject with a vision of what the language makes practical. http://www.pythonology.com/success The Python Software Foundation (PSF) has replaced the Python Consortium as an independent nexus of activity. It has official responsibility for Python's development and maintenance. http://www.python.org/psf/ Among the ways you can support PSF is with a donation. http://www.python.org/psf/donate.html Kurt B. Kaiser publishes a weekly report on faults and patches. http://www.google.com/groups?as_usubject=weekly%20python%20patch Although unmaintained since 2002, the Cetus collection of Python hyperlinks retains a few gems. http://www.cetus-links.org/oo_python.html Python FAQTS http://python.faqts.com/ The Cookbook is a collaborative effort to capture useful and interesting recipes. http://aspn.activestate.com/ASPN/Cookbook/Python Many Python conferences around the world are in preparation. Watch this space for links to them. Among several Python-oriented RSS/RDF feeds available are http://www.python.org/channews.rdf http://bootleg-rss.g-blog.net/pythonware_com_daily.pcgi http://python.de/backend.php For more, see http://www.syndic8.com/feedlist.php?ShowMatch=python&ShowStatus=all The old Python "To-Do List" now lives principally in a SourceForge reincarnation. http://sourceforge.net/tracker/?atid=355470&group_id=5470&func=browse http://www.python.org/dev/peps/pep-0042/ The online Python Journal is posted at pythonjournal.cognizor.com. editor(a)pythonjournal.com and editor(a)pythonjournal.cognizor.com welcome submission of material that helps people's understanding of Python use, and offer Web presentation of your work. del.icio.us presents an intriguing approach to reference commentary. It already aggregates quite a bit of Python intelligence. http://del.icio.us/tag/python *Py: the Journal of the Python Language* http://www.pyzine.com Archive probing tricks of the trade: http://groups.google.com/groups?oi=djq&as_ugroup=comp.lang.python&num=100 http://groups.google.com/groups?meta=site%3Dgroups%26group%3Dcomp.lang.pyth… Previous - (U)se the (R)esource, (L)uke! - messages are listed here: http://www.ddj.com/topic/python/ (requires subscription) http://groups-beta.google.com/groups?q=python-url+group:comp.lang.python*&s… http://purl.org/thecliff/python/url.html (dormant) or http://groups.google.com/groups?oi=djq&as_q=+Python-URL!&as_ugroup=comp.lan… There is *not* an RSS for "Python-URL!"--at least not yet. Arguments for and against are occasionally entertained. Suggestions/corrections for next week's posting are always welcome. E-mail to <Python-URL(a)phaseit.net> should get through. To receive a new issue of this posting in e-mail each Monday morning (approximately), ask <claird(a)phaseit.net> to subscribe. Mention "Python-URL!". Write to the same address to unsubscribe. -- The Python-URL! Team-- Phaseit, Inc. (http://phaseit.net) is pleased to participate in and sponsor the "Python-URL!" project. Watch this space for upcoming news about posting archives.

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Doubts about how implementing asynchronous timeouts through a heap
by Giampaolo Rodola' Aug. 5, 2008

Aug. 5, 2008

Hi, I'm trying to implement an asynchronous scheduler for asyncore to call functions at a later time without blocking the main loop. The logic behind it consists in: - adding the scheduled functions into a heapified list - calling a "scheduler" function at every loop which checks the scheduled functions due to expire soonest Note that, by using a heap, the first element of the list is always supposed to be the one with the lower timeout. Here's the code I wrote: <--- snippet ---> import heapq import time import sys delayed_map = [] class delayed_call: """Calls a function at a later time. The instance returned is an object that can be used to cancel the scheduled call, by calling its cancel() method. It also may be rescheduled by calling delay() or reset()} methods. """ def __init__(self, delay, target, *args, **kwargs): """ - delay: the number of seconds to wait - target: the callable object to call later - args: the arguments to call it with - kwargs: the keyword arguments to call it with """ assert callable(target), "%s is not callable" %target assert sys.maxint >= delay >= 0, "%s is not greater than or equal " \ "to 0 seconds" % (delay) self.__delay = delay self.__target = target self.__args = args self.__kwargs = kwargs # seconds from the epoch at which to call the function self.timeout = time.time() + self.__delay self.cancelled = False heapq.heappush(delayed_map, self) def __le__(self, other): return self.timeout <= other.timeout def active(self): """Return True if this scheduler has not been cancelled.""" return not self.cancelled def call(self): """Call this scheduled function.""" self.__target(*self.__args, **self.__kwargs) def reset(self): """Reschedule this call resetting the current countdown.""" assert not self.cancelled, "Already cancelled" self.timeout = time.time() + self.__delay if delayed_map[0] is self: heapq.heapify(delayed_map) def delay(self, seconds): """Reschedule this call for a later time.""" assert not self.cancelled, "Already cancelled." assert sys.maxint >= seconds >= 0, "%s is not greater than or equal " \ "to 0 seconds" %(seconds) self.__delay = seconds self.reset() def cancel(self): """Unschedule this call.""" assert not self.cancelled, "Already cancelled" del self.__target, self.__args, self.__kwargs if self in delayed_map: if delayed_map[0] is self: delayed_map.remove(self) heapq.heapify(delayed_map) else: delayed_map.remove(self) self.cancelled = True def fun(arg): print arg a = delayed_call(0.6, fun, '0.6') b = delayed_call(0.5, fun, '0.5') c = delayed_call(0.4, fun, '0.4') d = delayed_call(0.3, fun, '0.3') e = delayed_call(0.2, fun, '0.2') f = delayed_call(0.1, fun, '0.1') while delayed_map: now = time.time() while delayed_map and now >= delayed_map[0].timeout: delayed = heapq.heappop(delayed_map) try: delayed.call() finally: if not delayed.cancelled: delayed.cancel() time.sleep(0.01) </--- snippet ---> Here comes the questions. Since that the timeouts of the scheduled functions contained in the list can change when I reset() or cancel() them I don't know exactly *when* the list needs to be heapified(). By doing some tests I came to the conclusion that I need the heapify() the list only when the function I reset() or cancel() is the *first of the list* but I'm not absolutely sure about it. When do you think it would be necessary calling heapify()? I wrote a short test suite which tests the code above and I didn't notice strange behaviors but since that I don't know much about the logic behind heaps I'd need some help. Thanks a lot in advance. --- Giampaolo http://code.google.com/p/pyftpdlib/

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Re: Python FTP - NameError: name 'mydpa' is not defined
by MRAB Aug. 5, 2008

Aug. 5, 2008

On Jul 28, 2:27 pm, "Harry" <laiyi...(a)yahoo.ca> wrote: > Hi there. I am trying to download a file(sn.last) from a public FTP > server with the following code: > > from ftplib import FTP > ftp=FTP('tgftp.nws.noaa.gov') > ftp.login() > ftp.cwd('SL.us008001/DF.of/DC.radar/DS.81dpr/SI.kbuf') > ftp.retrbinar('RETR sn.last', open(mydpa,'wb').write) open(mydpa,'wb') would open the file to which you're saving the data, but you haven't defined to mydpa, so Python will complain. > ftp.quit() > > but got an error message, which I think is normal: > > Traceback (most recent call last): > File "<pyshell#13>", line 1, in <module> > ftp.retrbinary('RETR sn.last', open(mydpa,'wb').write) > NameError: name 'mydpa' is not defined Yep! > > I don't know much about python, but just try to use the code to > download data. I don't know where the file will be saved to. Is the > mydata a file name or a folder name? where will it be saved to even > if it's working? Please help be fixed the problem step by step? I am > using 2.5.2 by the way. > You need to tell it where to save the data by defining mydpa. > I really appreciate your help. Thanks.

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Hobbyist - Python vs. other languages
by fprintf Aug. 5, 2008

Aug. 5, 2008

I have been playing with computers since I first learned to program moving shapes on an Atari 800XL in BASIC. After many years of dabbling in programming languages as a hobbyist (I am not a computer scientist or other IT professional), I have never found a way to stick with a language far enough to do anything useful. I learn all about loops and data structures and functions/methods etc. but never get to create a program that will do anything of value that I can't more easily do via freeware. Well, except the slot car timing system I wrote in C++ for Linux many moons ago. Honestly Python seems like a breath of fresh air and possibly a way to get back to my BASIC roots, you know, programming just for the fun of it. Since I don't have a specific problem to solve, besides Pythonchallenge (which I found very cryptic), and Project Euler (which I found beyond my mathematics skills), is there a place to go for increasingly difficult problems to solve? I have followed a number of the recommended online tutorials that contain a logical progression of problems and yet they all end at the point where a person has enough knowledge of the syntax, but not really enough to do anything.

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Newbie Python questions
by LessPaul Aug. 4, 2008

Aug. 4, 2008

I recently discovered Python and see it as a great language to use for personal projects (and more). I made my living for over a decade as a coder in C, C++, ADA, Fortran, and Assembly before moving to systems engineering. I'm now retired, and would love to code again. I see Python as the perfect language to get a good program working in a short time. My question is in regard to GUI platforms. My primary target would be Windows, but I would also like be able to support Linux and Mac versions if possible. I'm also interested in using a system that also has support for pure C++ applications. As such, and after reading many web pages regarding Python GUIs, I believe I have the candidates narrowed down to pyQT and wxPython. The first question -- how steep is the curve to become proficient with the above GUI packages? If the answer is "not very" then there is no need for the following questions as I can try both on for size to see which I like best. However if it is a sizable investment in time, I'd like to maximize my efforts and choose the one I'll end up using in the end. The biggest hurdle I can see is the cost of the QT licence for commercial software, though apparently it can be acquired for a reasonable price via the BlackAdder package. Does purchasing the BlackAdder also include the needed software support for C++ development? Does the BlackAdder purchase also allow for licence of standard C++ apps? Since there appears to be no commercial licencing fee for wxWidgets/ wxPython, the last question is what do I gain from going QT over wx? I've seen great applications written with both (on my computer I have the wxPython Digsby and the pyQT apps "Mnemosyne" and "Anki". All seem to be solid.

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Bidirectional Generators
by william tanksley Aug. 4, 2008

Aug. 4, 2008

Okay, I'm almost finished with my first bidirectional generator. By "almost finished" I mean both that it's almost working, and that I'm almost about to replace it with a class that works a bit more like what I currently understand. Surely some other people have worked with this feature... Are there any pages that discuss how it's been useful? No, I don't want to see an implementation of coroutines. I get that one already. :-) -Wm

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