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  • Seeking enlightenment - global variables in AppEngine (aeoid.get_current_user())

    - by jerd
    Hello This may be a 'Python Web Programming 101' question, but I'm confused about some code in the aeoid project (http://github.com/Arachnid/aeoid). here's the code: _current_user = None def get_current_user(): """Returns the currently logged in user, or None if no user is logged in.""" global _current_user if not _current_user and 'aeoid.user' in os.environ: _current_user = User(None, _from_model_key=os.environ['aeoid.user']) return _current_user But my understanding was that global variables were, ehm, global! And so different requests from different users could (potentially) access and update the same value, hence the need for sessions, in order to store per-user, non-global variables. So, in the code above, what prevents one request from believing the current user is the user set by another request? Sorry if this is basic, it's just not how i thought things worked. Thanks

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  • Error Domain=SKErrorDomain Code=3 UserInfo=0x2a5a00 "Cannot connect to iTunes Store"

    - by SKk
    I am trying to implement InApp purchase in my application. I have implemented it as per Apple's programming guide and it(code) was working fine until I created new application, appid, provisioning profile and in-app products @ another developer account. Now, it gives me following error. Error Domain=SKErrorDomain Code=3 UserInfo=0x2a5a00 "Cannot connect to iTunes Store" Same code works fine if I use previous developer account's appid, pro-certificate and product ids. This is very strange issue, I double checked product id names and other things still facing same error. Any clue..?

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  • Roadblocks in creating a custom operating system

    - by Dinah
    It seems to me that the most common overly ambitious project that programmers (esp. Comp. Sci. grads) try to tackle is building your own operating system. (Trying to create your own programming language + compiler is probably even more common but not nearly as ambitious.) For those (like myself) foolish enough to try: aside from the sheer size, what are the biggest *gotcha*s or unexpected roadblocks you've encountered in trying to create your own OS from the ground up? Edit: A great OS question: http://stackoverflow.com/questions/43180/how-to-get-started-in-operating-system-development/

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  • append a numpy array to a numpy array

    - by Fraz
    I just started programming in python and am very new to numpy packages.. so still trying to get a hang of it. I have a an numpy_array so something like [ a b c] And then I want to append it into anotehr numpyarray (Just like we create a list of lists) How do we create an array of numpy arrays containing numpy arrays I tried to do the following without any luck >>> M = np.array([]) >>> M array([], dtype=float64) >>> M.append(a,axis=0) Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'numpy.ndarray' object has no attribute 'append' >>> a array([1, 2, 3])

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  • Clojure editor/IDE recommendations on OS X

    - by Julien Chastang
    I am starting to learn the Clojure programming language. Are there any recommendations for Clojure editors/IDEs on OS X? Update 2009-9-23: The clojure space has changed tremendously since I originally posted this question. Many of the links below, especially those that refer to clojure-mode with emacs, are out-of-date. The best clojure IDE I found was the enclojure Netbeans plugin which was recently released (2009-08-25). Update 2010-4-30: Here is another very good link on this subject by Lau B. Jensen. Also, for my own clojure development, I have actually moved to emacs / swank-clojure.

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  • The Zen of Python distils the guiding principles for Python into 20 aphorisms but lists only 19. What's the twentieth?

    - by Jeff Walden
    From PEP 20, The Zen of Python: Long time Pythoneer Tim Peters succinctly channels the BDFL's guiding principles for Python's design into 20 aphorisms, only 19 of which have been written down. What is this twentieth aphorism? Does it exist, or is the reference merely a rhetorical device to make the reader think? (One potential answer that occurs to me is that "You aren't going to need it" is the remaining aphorism. If that were the case, it would both exist and act to make the reader think, and it would be characteristically playful, thus fitting the list all the better. But web searches suggest this to be an extreme programming mantra, not intrinsically Pythonic wisdom, so I'm stumped.)

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  • Language Design: Combining Gotos and Functions

    - by sub
    I'm designing and currently rethinking a low-level interpreted programming language with similarities to assembler. I very soon came across the functions/loops/gotos decision problem and thought that while loops like while and for would be too high-level and unfitting, gotos would be too low level, unmaintainable and generally evil again. Functions like you know them from most languages that have return values and arguments aren't fitting in the language's concept either. So I tried to figure out something between a function and a goto which is capable of Recursion Efficient loops After some thinking I came up with the idea of subroutines: They have a beginning and an end like a function They have a name but no arguments like a goto You can go into one with jump and go out of it again before its end with return (doesn't give back any result, only stops the subroutine) Handled just like normal code - Global scope like goto So I wanted to know: Is the idea above good? What are the (dis)advantages? Would there be a better combination of function and goto or even a completely new idea?

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  • Subversion vision and roadmap

    - by gbjbaanb
    Recently C Michael Pilato of the core subversion team posted a mail to the subversion dev mailing list suggesting a vision and roadmap for the future of Subversion. Naturally, he wanted as much feedback and response as possible which is why I'm posting this here - to elicit some suggestions and contributions from you, the administrators of Subversion. Any comments are welcome, and I shall feedback a synopsis with a link to this question to the dev mailing list. Similarly, I've created a post on StackOverflow to get feedback from the programmer/user side of things too. So, without further ado: Vision The first thing on his "vision statement" is: Subversion has no future as a DVCS tool. Let's just get that out there. At least two very successful such tools exist already, and to squeeze another horse into that race would be a poor investment of energy and talent. There's no need to suggest distributed features for subversion. If you want a DVCS, there should be no ill-feeling if you migrate to Git, Mercurial or Bazaar. As he says, its pointless trying to make SVN like them when they already exist, especially when there are different usage patterns that SVN should be targetting. The vision for Subversion is: Subversion exists to be universally recognized and adopted as an open-source, centralized version control system characterized by its reliability as a safe haven for valuable data; the simplicity of its model and usage; and its ability to support the needs of a wide variety of users and projects, from individuals to large-scale enterprise operations. Roadmap Several ideas were suggested as being "very nice to have" and are offered as the starting point of a future roadmap. These are: Obliterate Shelve/Checkpoint Repository-dictated Configuration Rename Tracking Improved Merging Improved Tree Conflict Handling Enterprise Authentication Mechanisms Forward History Searching Log Message Templates Repository-dictated Configuration If anyone has suggestions to add, or comments on these, the subversion community would welcome all of them. Community And lastly, there was a call for more people to become involved with Subversion development. As with most OSS projects it can be daunting to join, but there is now a push for more to be done to help. If you feel like you can contribute, please do so.

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  • Resizing screenshots/screen captures for inclusion in Beamer

    - by Stephen
    Sorry, this may or may not be a programming question directly, but I am trying to resize screenshots with Imagemagick and Gimp to include in a Beamer presentation, but it comes out even blurrier than the resizing done by LaTeX. For instance, in Beamer I might have a command to rescale the image \includegraphics[width=.5\textwidth]{fig.png}. Using something like \begin{frame} \message{width = \the\textwidth} \message{height = \the\textheight} \end{frame} I have gotten the \textwidth and \textheight parameters in points (345.69548, 261.92444). So I have a script (in Python) that sends a system call to Imagemagick: 'convert %s -resize %.6f@ resized_%s' % (f,a,f) where a is calculated as \textwidth*\textheight*0.5**2. When I then go back into my Beamer presentation and include the resized figure, \includegraphics{resized_fig.png}, the size looks approximately correct but it's super-blurry. I also tried resizing in Gimp (using the GUI) but no luck either... help? Thanks...

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  • Perl for a Python programmer

    - by fortran
    I know Python (and a bunch of other languages) and I think it might be nice to learn Perl, even if it seems that most of the people is doing it the other way around... My main concern is not about the language itself (I think that part is always easy), but about learning the Perlish (as contrasted with Pythonic) way of doing things; because I don't think it'll be worth the effort if I end up programming Python in Perl. So my questions are basically two: Are there many problems/application areas where it's actually more convenient to solve them in Perl rather than in Python? If the first question is positive, where can I found a good place to get started and learn best practices that is not oriented to beginners?

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  • Relating NP-Complete problems to real world problems

    - by terru
    I have a decent grasp of NP Complete problems; that's not the issue. What I don't have is a good sense of where they turn up in "real" programming. Some (like knapsack and traveling salesman) are obvious, but others don't seem obviously connected to "real" problems. I've had the experience several times of struggling with a difficult problem only to realize it is a well known NP Complete problem that has been researched extensively. If I had recognized the connection more quickly I could have saved quite a bit of time researching existing solutions to my specific problem. Are there any resources (online or print) that specifically connect NP Complete to real world instances?

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  • Career advice for a frustrated newbie programmer.

    - by Satoru.Logic
    Hi, all. This is my first year as a programmer. The programming language that I'm most familiar with is Python. I am maintaining a web2py based legacy system, alone, which means I have to grow up as an all-rounder. The original programmers on this project are nowhere to find, and there are hardly any usable documents about requirements or anything. I find it very frustrating every time I hear the users criticize the system, and I can't help explaining that "that was not my fault, those mess was there even before I entered this company." I wonder what should I do with this situation. Please give me some advice, thanks in advance.

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  • String Formatting Tricks/Docs

    - by Meltemi
    Was reading the response by Shaggy Frog to this post and was intrigued by the following line of code: NSLog(@"%@", [NSString stringWithFormat:@"%@:%*s%5.2f", key, padding, " ", [object floatValue]]); I know string formatting is an age old art but I'm kinda doing the end around into Cocoa/Obj-C programming and skipped a few grades along the way. Where is a good (best) place to learn all the string formatting tricks allowed in NSString's stringWithFormat? I'm familiar with Apple's String Format Specifiers page but from what I can tell it doesn't shed light on whatever is happening with %*s or the %5.2f (not to mention the 3 apparent placeholders followed by 4 arguments) above?!?

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  • Looking for calculator source code, BSD-licensed

    - by Horace Ho
    I have an urgent project which need many functions of a calculator (plus a few in-house business rule formulas). As I won't have time to re-invent the wheel so I am looking for source code directly. Requirements: BSD licensed (GPL won't help) in c/c++ programming language 32-bit CPU minimum dependency on platform API/data structure best with both RPN and prefix notation supported emulator/simulator code also acceptable (if not impossible to add custom formula) with following functions (from wikipedia) Scientific notation for calculating large numbers floating point arithmetic logarithmic functions, using both base 10 and base e trigonometry functions (some including hyperbolic trigonometry) exponents and roots beyond the square root quick access to constants such as pi and e plus hexadecimal, binary, and octal calculations, including basic Boolean math fractions optional statistics and probability calculations complex numbers programmability equation solving

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  • Email sent by ActionMailer is taking six hours to deliver mail.

    - by grg-n-sox
    So I have been asked to help maintain a website that uses Ruby on Rails. Now, let me just say I've been programming Ruby for awhile but I am still new to Rails. The first problem brought to my attention is how the activation email takes about six hours to arrive. It would be one thing if the email was not being sent due to errors but it is being send correctly, just slow. Also the server this is running on is also its own SMTP. I checked how the email was being formatted before calling the setup_email method and everything looks okay. I even dug into the ActionMailer lib and read through the files there and didn't see anything out of the ordinary. So what is most likely causing the email to take six hours to deliver?

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  • .NET or Windows Synchronization Primitives Performance Specifications

    - by ovanes
    Hello *, I am currently writing a scientific article, where I need to be very exact with citation. Can someone point me to either MSDN, MSDN article, some published article source or a book, where I can find performance comparison of Windows or .NET Synchronization primitives. I know that these are in the descending performance order: Interlocked API, Critical Section, .NET lock-statement, Monitor, Mutex, EventWaitHandle, Semaphore. Many Thanks, Ovanes P.S. I found a great book: Concurrent Programming on Windows by Joe Duffy. This book is written by one of the head concurrency developers for .NET Framework and is simply brilliant with lots of explanations, how things work or were implemented.

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  • Reading multiple Emacs info files simultaneously

    - by pajato0
    For reading programming (and other) documentation, the Emacs INFO mode is outstanding. So outstanding that I would like to be able to read say, the Emacs Lisp info file and the org-mode info files simultaneously without traversing back up to the beginning of the info tree. Either I've missed something obvious or I will need to hack some Emacs Lisp to achieve the goal. And yet again, someone may have already cracked this nut. So I guess my question is: what is the state of the practice for reading mulitple INFO files in Emacs simultaneously?

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  • What web-development platform should I use considering Time-To-Market?

    - by Jonas
    I have been looking at a few differend platforms for my coming web-development project. I would like to hear what web-development platform is recommended when considering Time-To-Maket. Suppose that I already know the programming language well, but not the web-framework. The OS will be Linux. My requirements and priorities: Time-To-Market RESTful Maintainable code Scales-up (not dog-slow) The one I have looked at but never used are: Java and Play! Framework or GWT Python and Django PHP and Zend Framework Ruby and Ruby on Rails Erlang and Nitrogen and Webmachine Scala and Lift C++ and Wt C# and ASP.NET Mono It's a bonus if the framework has support for making sites for mobile phones.

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  • Aaron Hillegass Chapter 18 Challenge Question

    - by jasonbogd
    I am working through Aaron Hillegass' Cocoa Programming for Mac OS X and am doing the challenge for Chapter 18. Basically, the challenge is to write an app that can draw ovals using your mouse, and then additionally, add saving/loading and undo support. I'm trying to think of a good class design for this app that follows MVC. Here's what I had in mind: Have a NSView-subclass that represents an oval (say JBOval) that I can use to easily draw an oval. Have a main view (JBDrawingView) that holds JBOvals and draws them. The thing is that I wasn't sure how to add archiving. Should I archive each JBOval? I think this would work, but archiving an NSView doesn't seem very efficient. Any ideas on a better class design? Thanks.

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  • A strong case for WF

    - by Pita.O
    Hi guys, I have struggled for so long to find a compelling use case for workflow (ie: WF) as against regular imperative programming. Each time I fall back to the conclusion that I should just leave WF out or defer getting into it until later. But I keep having this nagging feeling that there's something am missing. Does anyone know any book that truly makes a strong case for the Workflow way? The book has to (i) teach WF well, and (ii) show using appropriate use cases that WF made an implementation easy to do than if we just did our regular straight coding. I will appreciate it.

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  • How to create playable FLV video from part of FLV file using FFMPEG?

    - by Ole Jak
    So we had real FLV video file. we had devided it into 3 parts (more or less equal, not looking into structure orcontext). We have taken second part and forgot about first 2. Video contained audio and video track. mp3 and on vp6. Is it any how possible to play thsat second part after sending to ffmpeg some command? So how to (using any FFMPEG API (in general in any programming language) or using command line) turn bytearray into playable video? (knowing what format video was created in and some other data like used codecs )

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  • iPhone Foundation - performance implications of mutable and xxxWithCapacity:0

    - by Adam Eberbach
    All of the collection classes have two versions - mutable and immutable, such as NSArray and NSMutableArray. Is the distinction merely to promote careful programming by providing a const collection or is there some performance hit when using a mutable object as opposed to immutable? Similarly each of the collection classes has a method xxxxWithCapacity, like [NSMutableArray arrayWithCapacity:0]. I often use zero as the argument because it seems a better choice than guessing wrongly how many objects might be added. Is there some performance advantage to creating a collection with capacity for enough objects in advance? If not why isn't the function something like + (id)emptyArray?

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  • Why can't I download a whole image file with urllib2.urlopen()

    - by John Gann
    When I run the following code, it only seems to be downloading the first little bit of the file and then exiting. Occassionally, I will get a 10054 error, but usually it just exits without getting the whole file. My internet connection is crappy wireless, and I often get broken downloads on larger files in firefox, but my browser has no problem getting a 200k image file. I'm new to python, and programming in general, so I'm wondering what nuance I'm missing. import urllib2 xkcdpic=urllib2.urlopen("http://imgs.xkcd.com/comics/literally.png") xkcdpicfile=open("C:\\Documents and Settings\\John Gann\\Desktop\\xkcd.png","w") while 1: chunk=xkcdpic.read(4028) if chunk: print chunk xkcdpicfile.write(chunk) else: break

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  • Distributing APNS providers

    - by Sam
    I'm writing a business-focused iPhone app which includes a self-hosted server component. I'd like to include push notification functionality in the server; reading through the programming guide it looks as if this would involve either: Distributing the provider certificate with the server component - this doesn't sound like a terribly good idea (even if Apple permits it?) Hosting a shared notification provider and forwarding notifications to APNS from the servers. For an ongoing, high-availability service, this is likely to require including a subscription pricing component, which I would prefer to avoid. Require customers to apply for their own provider certificate. However, it's not clear whether multiple organisations are allowed to apply for provider certificates with a single bundle ID, and it would significantly increase the barrier to adoption. APNS looks to me as if it's specifically geared for centrally hosted services. Is anyone distributing self-hosted notification providers? Are there any other options?

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  • In search of a network file system with extended caching to speed up file access

    - by Brecht Machiels
    I'm running a small home server that stores my documents. The disks in this server are in a RAID 1 configuration (using Linux md) and it's also periodically being backup up to an external hard drive to make sure I don't lose them. However, I'm always accessing the files from other computers on the home network using an SMB share, and this results in a considerable speed penalty (especially when connected over WLAN). This is quite annoying when editing large files, such as digital camera RAWs, for example. I've been looking for a solution to this problem. It would have to offer some kind of local caching to speed up the file access. The client would preferably not keep a copy of all data on the server, as it consists of a very large collection of photographs, most of which I will not access frequently. Instead, it should only cache the accessed files and sync the changes back in the background. Ideally, it would also do some smart read-ahead (cache the files that are in the same directory as the currently opened file, for examples), but I suppose that's asking a bit much. Synchronization should be automatic (on file change). Conflicting file changes (at the same time on different clients) are unlikely to happen in my use case, but I would prefer if they are handled properly (notification to the user). I've come across the following options, so far: something similar to Dropbox. iFolder seems to be the only thing that comes close, but its reputation (stability) and requirements put me off. A distributed file system such as OpenAFS. I'm not sure this will speed up file access. It is probably overkill for what I need. Maybe NFS or even Samba offer these possibilities. I read a bit about Windows' Offline Files, but its operation seems limited (at least on Windows XP). As this is just for personal use, I'm not willing to spend a lot of money. A free solution would be preferred. Also, the server needs to run on Linux, and I need a client for at least Windows.

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