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• What are the parameters that let businesses choose .NET or Java over other languages/frameworks? [on hold]

  - by Othman

  Some of the biggest enterprise applications such as HR software, Sales and ERP, are written in .NET or Java. Also, Governments online solutions such as paying parking fines, and universities courses registration systems are all in .NET or Java. On the other hand, Facebook, Google and Wikipedia, are not using .NET or Java so much (Google uses at least both Java and Python). Twitter also was using Ruby for a long time, as well as Python. These websites work on much more data and at larger scales in terms of users and performance than any enterprise applications, yet still these companies have chosen a different path. What are the parameters driving such decisions? Note This question is not about why do you prefer x over y! or why those people are using this. The question is primarily asking about the parameters that makes Java Or .NET becomes better suite in enterprise applications based on Performance, Reliability, Scalability etc.

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• What interface does python use to implement sockets?

  - by user2738698

  When I programmed in python, I believe I interfaced with the transport layer using sockets. If python was programmed by humans, they must have used an interface that was "lower" than sockets, to provide us with the interface to sockets. I assume firewalls, also programmed by humans, use interfaces of lower layers in the same manner, so is there a way to access such lower layers, in terms of programming?

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• How do I create a custom python interpreter? i.e. with certain modules already included?

  - by Johnny Brown

  If you've used Ruby on Rails, I'm thinking of the feature where the user types 'rails console' and instantly gets a Ruby console with rails and the current app already loaded. I want to make something like this for a python program I'm working on, does anyone know how I would get to type say, 'python myPythonConsole.py' and open up a regular python interpreter but with my program and all its dependencies loaded?

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• How do I copy a python function to a remote machine and then execute it?

  - by Hugh

  I'm trying to create a construct in Python 3 that will allow me to easily execute a function on a remote machine. Assuming I've already got a python tcp server that will run the functions it receives, running on the remote server, I'm currently looking at using a decorator like @execute_on(address, port) This would create the necessary context required to execute the function it is decorating and then send the function and context to the tcp server on the remote machine, which then executes it. Firstly, is this somewhat sane? And if not could you recommend a better approach? I've done some googling but haven't found anything that meets these needs. I've got a quick and dirty implementation for the tcp server and client so fairly sure that'll work. I can get a string representation the function (e.g. func) being passed to the decorator by import inspect string = inspect.getsource(func) which can then be sent to the server where it can be executed. The problem is, how do I get all of the context information that the function requires to execute? For example, if func is defined as follows, import MyModule def func(): result = MyModule.my_func() MyModule will need to be available to func either in the global context or funcs local context on the remote server. In this case that's relatively trivial but it can get so much more complicated depending on when and how import statements are used. Is there an easy and elegant way to do this in Python? The best I've come up with at the moment is using the ast library to pull out all import statements, using the inspect module to get string representations of those modules and then reconstructing the entire context on the remote server. Not particularly elegant and I can see lots of room for error. Thanks for your time

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• Are there some cases where Python threads can safely manipulate shared state?

  - by erikg

  Some discussion in another question has encouraged me to to better understand cases where locking is required in multithreaded Python programs. Per this article on threading in Python, I have several solid, testable examples of pitfalls that can occur when multiple threads access shared state. The example race condition provided on this page involves races between threads reading and manipulating a shared variable stored in a dictionary. I think the case for a race here is very obvious, and fortunately is eminently testable. However, I have been unable to evoke a race condition with atomic operations such as list appends or variable increments. This test exhaustively attempts to demonstrate such a race: from threading import Thread, Lock import operator def contains_all_ints(l, n): l.sort() for i in xrange(0, n): if l[i] != i: return False return True def test(ntests): results = [] threads = [] def lockless_append(i): results.append(i) for i in xrange(0, ntests): threads.append(Thread(target=lockless_append, args=(i,))) threads[i].start() for i in xrange(0, ntests): threads[i].join() if len(results) != ntests or not contains_all_ints(results, ntests): return False else: return True for i in range(0,100): if test(100000): print "OK", i else: print "appending to a list without locks *is* unsafe" exit() I have run the test above without failure (100x 100k multithreaded appends). Can anyone get it to fail? Is there another class of object which can be made to misbehave via atomic, incremental, modification by threads? Do these implicitly 'atomic' semantics apply to other operations in Python? Is this directly related to the GIL?

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• Reusing OAuth request token when user refresh page - Twitter4j on GAE

  - by Tahir Akram

  Hi I am using Twitter4J API on GAE/J. I want to use the request token when user came to my page. (called back URL). And press refresh button. I write following code for that. But When user press refresh button. I got Authentication credentials error. Please see the stacktrance. It works fine when user first time used that token. HomeServlet.java code: HttpSession session = request.getSession(); twitter.setOAuthConsumer(FFConstants.CONSUMER_KEY, FFConstants.CONSUMER_SECRET); String token = (String) session.getAttribute("token"); String authorizedToken = (String)session.getAttribute("authorizedToken"); User user = null; if (!token.equals(authorizedToken)){ AccessToken accessToken = twitter.getOAuthAccessToken( token, (String) session .getAttribute("tokenSecret")); twitter.setOAuthAccessToken(accessToken); user = twitter.verifyCredentials(); session.setAttribute("authorizedToken", token); session.setAttribute("user", user); }else{ user = (User)session.getAttribute("user"); } TwitterUser twitterUser = new TwitterUser(); twitterUser.setFollowersCount(user.getFollowersCount()); twitterUser.setFriendsCount(user.getFriendsCount()); twitterUser.setFullName(user.getName()); twitterUser.setScreenName(user.getScreenName()); twitterUser.setLocation(user.getLocation()); Please suggest how I can do that. I have seen on many website. They retain the user with the same token. Even if user press browser refresh buttion again and again. Please help. Exception stacktrace: Reason: twitter4j.TwitterException: 401:Authentication credentials were missing or incorrect. /friends/ids.xml This method requires authentication. at twitter4j.http.HttpClient.httpRequest(HttpClient.java:469) at twitter4j.http.HttpClient.get(HttpClient.java:412) at twitter4j.Twitter.get(Twitter.java:276) at twitter4j.Twitter.get(Twitter.java:228) at twitter4j.Twitter.getFriendsIDs(Twitter.java:1819) at com.tff.servlet.HomeServlet.doGet(HomeServlet.java:86) at javax.servlet.http.HttpServlet.service(HttpServlet.java:693) at javax.servlet.http.HttpServlet.service(HttpServlet.java:806) at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1093) at com.google.apphosting.utils.servlet.ParseBlobUploadFilter.doFilter(ParseBlobUploadFilter.java:97) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084) at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084) at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084) at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:360) at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216) at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181) at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:712) at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405) at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:238) at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:139) at org.mortbay.jetty.Server.handle(Server.java:313) at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:506) at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:830) at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76) at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:381) at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:135) at com.google.apphosting.runtime.JavaRuntime.handleRequest(JavaRuntime.java:235) at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:5235) at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:5233) at com.google.net.rpc.impl.BlockingApplicationHandler.handleRequest(BlockingApplicationHandler.java:24) at com.google.net.rpc.impl.RpcUtil.runRpcInApplication(RpcUtil.java:363) at com.google.net.rpc.impl.Server$2.run(Server.java:838) at com.google.tracing.LocalTraceSpanRunnable.run(LocalTraceSpanRunnable.java:56) at com.google.tracing.LocalTraceSpanBuilder.internalContinueSpan(LocalTraceSpanBuilder.java:536) at com.google.net.rpc.impl.Server.startRpc(Server.java:793) at com.google.net.rpc.impl.Server.processRequest(Server.java:368) at com.google.net.rpc.impl.ServerConnection.messageReceived(ServerConnection.java:448) at com.google.net.rpc.impl.RpcConnection.parseMessages(RpcConnection.java:319) at com.google.net.rpc.impl.RpcConnection.dataReceived(RpcConnection.java:290) at com.google.net.async.Connection.handleReadEvent(Connection.java:466) at com.google.net.async.EventDispatcher.processNetworkEvents(EventDispatcher.java:759) at com.google.net.async.EventDispatcher.internalLoop(EventDispatcher.java:205) at com.google.net.async.EventDispatcher.loop(EventDispatcher.java:101) at com.google.net.rpc.RpcService.runUntilServerShutdown(RpcService.java:251) at com.google.apphosting.runtime.JavaRuntime$RpcRunnable.run(JavaRuntime.java:394) at java.lang.Thread.run(Unknown Source)

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• How do I read binary C++ protobuf data using Python protobuf?

  - by nbolton

  The Python version of Google protobuf gives us only: SerializeAsString() Where as the C++ version gives us both: SerializeToArray(...) SerializeAsString() We're writing to our C++ file in binary format, and we'd like to keep it this way. That said, is there a way of reading the binary data into Python and parsing it as if it were a string? Is this the correct way of doing it? binary = get_binary_data() binary_size = get_binary_size() string = None for i in range(len(binary_size)): string += i message = new MyMessage() message.ParseFromString(string) Update: Here's a new example, and a problem: message_length = 512 file = open('foobars.bin', 'rb') eof = False while not eof: data = file.read(message_length) eof = not data if not eof: foo_bar = FooBar() foo_bar.ParseFromString(data) When we get to the foo_bar.ParseFromString(data) line, I get this error: Exception Type: DecodeError Exception Value: Too many bytes when decoding varint. Update 2: It turns out, that the padding on the binary data was throwing protobuf off; too many bytes were being sent in, as the message suggests (in this case it was referring to the padding). This padding comes from using the C++ protobuf function, SerializeToArray on a fixed-length buffer. To eliminate this, I have used this temproary code: message_length = 512 file = open('foobars.bin', 'rb') eof = False while not eof: data = file.read(message_length) eof = not data string = '' for i in range(0, len(data)): byte = data[i] if byte != '\xcc': # yuck! string += data[i] if not eof: foo_bar = FooBar() foo_bar.ParseFromString(string) There is a design flaw here I think. I will re-implement my C++ code so that it writes variable length arrays to the binary file. As advised by the protobuf documentation, I will prefix each message with it's binary size so that I know how much to read when I'm opening the file with Python.

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• Why can't I include these data files in a Python distribution using distutils?

  - by froadie

  I'm writing a setup.py file for a Python project so that I can distribute it. The aim is to eventually create a .egg file, but I'm trying to get it to work first with distutils and a regular .zip. This is an eclipse pydev project and my file structure is something like this: ProjectName src somePackage module1.py module2.py ... config propsFile1.ini propsFile2.ini propsFile3.ini setup.py Here's my setup.py code so far: from distutils.core import setup setup(name='ProjectName', version='1.0', packages=['somePackage'], data_files = [('config', ['..\config\propsFile1.ini', '..\config\propsFile2.ini', '..\config\propsFile3.ini'])] ) When I run this (with sdist as a command line parameter), a .zip file gets generated with all the python files - but the config files are not included. I thought that this code: data_files = [('config', ['..\config\propsFile1.ini', '..\config\propsFile2.ini', '..\config\propsFile3.ini'])] indicates that those 3 specified config files should be copied to a "config" directory in the zip distribution. Why is this code not accomplishing anything? What am I doing wrong? (I have also tried playing around with the paths of the config files... But nothing seems to help. Would Python throw an error or warning if the path was incorrect / file was not found?)

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• Problem running python/matplotlib in background after ending ssh session.

  - by Jamie

  Hi there, I have to VPN and then ssh from home to my work server and want to run a python script in the background, then log out of the ssh session. My script makes several histogram plots using matplotlib, and as long as I keep the connection open everything is fine, but if I log out I keep getting an error message in the log file I created for the script. File "/Home/eud/jmcohen/.local/lib/python2.5/site-packages/matplotlib/pyplot.py", line 2058, in loglog ax = gca() File "/Home/eud/jmcohen/.local/lib/python2.5/site-packages/matplotlib/pyplot.py", line 582, in gca ax = gcf().gca(**kwargs) File "/Home/eud/jmcohen/.local/lib/python2.5/site-packages/matplotlib/pyplot.py", line 276, in gcf return figure() File "/Home/eud/jmcohen/.local/lib/python2.5/site-packages/matplotlib/pyplot.py", line 254, in figure **kwargs) File "/Home/eud/jmcohen/.local/lib/python2.5/site-packages/matplotlib/backends/backend_tkagg.py", line 90, in new_figure_manager window = Tk.Tk() File "/Home/eud/jmcohen/.local/lib/python2.5/lib-tk/Tkinter.py", line 1647, in __init__ self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use) _tkinter.TclError: couldn't connect to display "localhost:10.0" I'm assuming that it doesn't know where to create the figures I want since I close my X11 ssh session. If I'm logged in while the script is running I don't see any figures popping up (although that's because I don't have the show() command in my script), and I thought that python uses tkinter to display figures. The way that I'm creating the figures is, loglog() hist(list,x) ylabel('y') xlabel('x') savefig('%s_hist.ps' %source.name) close() The script requires some initial input, so the way I'm running it in the background is python scriptToRun.py << start>& logfile.log& Is there a way around this, or do I just have to stay ssh'd into my machine? Thanks.

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• How to I pass parameters to Ruby/Python scripts from inside PHP?

  - by Roger

  Hi, everybody. I need to turn HTML into equivalent Markdown-structured text. From what I could discover, I have only two good choices: Python: Aaron Swartz's html2text.py Ruby: Singpolyma's html2markdown.rb As I am programming in PHP, I need to pass the HTML code, call the Ruby/Python Script and receive the output back. I started creating a simple test just to know if my server was configured to run both languages. PHP code: echo exec('./hi.rb'); Ruby code: #!/usr/bin/ruby puts "Hello World!" It worked fine and I am ready to go to the next step. Unfortunately, all I know is that the function is Ruby works like this: HTML2Markdown.new('<h1>HTMLcode</h1>').to_s I don't know how to make PHP pass the string (with the HTML code) to Ruby nor how to make the ruby script receive the variable and pass it back to PHP (after have parsed it into Markdown). Believe it or not: I know less of Python. A folk made a similar question here ("how to call ruby script from php?") but with no practical information to my case. Any help would be a joy - thanks. Rogério Madureira. atipico.com.br

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• What are simple instructions for creating a Python package structure and egg?

  - by froadie

  I just completed my first (minor) Python project, and my boss wants me to package it nicely so that it can be distributed and called from other programs easily. He suggested I look into eggs. I've been googling and reading, but I'm just getting confused. Most of the sites I'm looking at explain how to use Python eggs that were already created, or how to create an egg from a setup.py file (which I don't yet have). All I have now is an Eclipse pydev project with about 4 modules and a settings/configuration file. In easy steps, how do I go about structuring it into folders/packages and compiling it into an egg? And once it's an egg, what do I have to know about deploying/building/using it? I'm really starting from scratch here, so don't assume I know anything; simple step-by-step instructions would be really helpful... These are some of the sites that I've been looking at so far: http://peak.telecommunity.com/DevCenter/PythonEggs http://www.packtpub.com/article/writing-a-package-in-python http://www.ibm.com/developerworks/library/l-cppeak3.html#N10232 I've also browsed a few SO questions but haven't really found what I need. Thanks!

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• How to use python to create a GUI application which have cool animation/effects under Linux (like 3D

  - by sgon00

  Hi, I am not sure if my question title makes sense to you or not. I am seeing many cool applications which have cool animations/effects. I would like to learn how to use python to create this kind of GUI applications under Linux. "cool animation/effects" like 3D wall in Cooliris which is written in flash and compiz effects with opengl. I also heard of some python GUI library like wxPython and pyQT. Since I am completely new to python GUI programming, can anyone suggest me where to start and what I should learn to achieve and create such application? maybe learn pyQT with openGL feature? pyopengl binding? I have no clue on where to start. thank you very much for your time and suggestion. By the way, in case if someone need to know which kind of application I am going to create, well, just any kind of applications. maybe photo explorer with 3D wall, maybe IM client, maybe facebook client etc...

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• Python CGI Premature end of script error depending on script parameters.

  - by nickengland

  I have a python script which should parse a file and produce some output to disk, as well as returning a webpage linking to the outputted files. When run with a file posted from the HTML form I get no HTML output back, just a 500 error page and the error_log contains the line: [Mon Apr 19 15:03:23 2010] [error] [client xxx.xxx.121.79] Premature end of script headers: uploadcml.py, referer: http://xxx.ch.cam.ac.uk:9000/ However, the files which the script should be saving are indeed saved to disk. If I run it without any arguments, the script returns the correct HTML indicating no file was parsed. All the information I have found on the web about Premature end of script headers implies it is due to either a missing header, or lack of permissions on the python script but neither can apply to me. The first lines of the script are: #!/home/nwe23/bin/bin/python import cgitb; cgitb.enable() import cgi import pybel,openbabel import random print "Content-Type: text/html" print so when run, I can see no way for it to fail to output the header, and it DOES output the header when run without a file to parse, but when given a file produces the error(but still parsed the file and saves the output to disk!). Does anyone know how this is happening and what can be done to fix it? I have tried adding wrongly-indented gibberish (such as foobar) at various points in the file, and this results in adding an indent error to the error_log wherever it is, even if its the very last line in the script. The Premature script headers error remains though. Does this mean the script is executing all the way through?

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• How to find Tomcat's PID and kill it in python?

  - by 4herpsand7derpsago

  Normally, one shuts down Apache Tomcat by running its shutdown.sh script (or batch file). In some cases, such as when Tomcat's web container is hosting a web app that does some crazy things with multi-threading, running shutdown.sh gracefully shuts down some parts of Tomcat (as I can see more available memory returning to the system), but the Tomcat process keeps running. I'm trying to write a simple Python script that: Calls shutdown.sh Runs ps -aef | grep tomcat to find any process with Tomcat referenced If applicable, kills the process with kill -9 <PID> Here's what I've got so far (as a prototype - I'm brand new to Python BTW): #!/usr/bin/python # Imports import sys import subprocess # Load from imported module. if __init__ == "__main__": main() # Main entry point. def main(): # Shutdown Tomcat shutdownCmd = "sh ${TOMCAT_HOME}/bin/shutdown.sh" subprocess.call([shutdownCmd], shell=true) # Check for PID grepCmd = "ps -aef | grep tomcat" grepResults = subprocess.call([grepCmd], shell=true) if(grepResult.length > 1): # Get PID and kill it. pid = ??? killPidCmd = "kill -9 $pid" subprocess.call([killPidCmd], shell=true) # Exit. sys.exit() I'm struggling with the middle part - with obtaining the grep results, checking to see if their size is greater than 1 (since grep always returns a reference to itself, at least 1 result will always be returned, methinks), and then parsing that returned PID and passing it into the killPidCmd. Thanks in advance!

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• Problems with Threading in Python 2.5, KeyError: 51, Help debugging?

  - by vignesh-k

  I have a python script which runs a particular script large number of times (for monte carlo purpose) and the way I have scripted it is that, I queue up the script the desired number of times it should be run then I spawn threads and each thread runs the script once and again when its done. Once the script in a particular thread is finished, the output is written to a file by accessing a lock (so my guess was that only one thread accesses the lock at a given time). Once the lock is released by one thread, the next thread accesses it and adds its output to the previously written file and rewrites it. I am not facing a problem when the number of iterations is small like 10 or 20 but when its large like 50 or 150, python returns a KeyError: 51 telling me element doesn't exist and the error it points out to is within the lock which puzzles me since only one thread should access the lock at once and I do not expect an error. This is the class I use: class errorclass(threading.Thread): def __init__(self, queue): self.__queue=queue threading.Thread.__init__(self) def run(self): while 1: item = self.__queue.get() if item is None: break result = myfunction() lock = threading.RLock() lock.acquire() ADD entries from current thread to entries in file and REWRITE FILE lock.release() queue = Queue.Queue() for i in range(threads): errorclass(queue).start() for i in range(desired iterations): queue.put(i) for i in range(threads): queue.put(None) Python returns with KeyError: 51 for large number of desired iterations during the adding/write file operation after lock access, I am wondering if this is the correct way to use the lock since every thread has a lock operation rather than every thread accessing a shared lock? What would be the way to rectify this?

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• In what order should the Python concepts be explained to absolute beginners?

  - by Tomaž Pisanski

  I am teaching Python to undergraduate math majors. I am interested in the optimal order in which students should be introduced to various Python concepts. In my view, at each stage the students should be able to solve a non-trivial programming problem using only the tools available at that time. Each new tool should enable a simpler solution to a familiar problem. A selection of numerous concepts available in Python is essential in order to keep students focused. They should also motivated and should appreciate each newly mastered tool without too much memorization. Here are some specific questions: For instance, my predecessor introduced lists before strings. I think the opposite is a better solution. Should function definitions be introduced at the very beginning or after mastering basic structured programming ideas, such as decisions (if) and loops (while)? Should sets be introduced before dictionaries? Is it better to introduce reading and writing files early in the course or should one use input and print for most of the course? Any suggestions with explanations are most welcome.

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• Python file iterator over a binary file with newer idiom.

  - by drewk

  In Python, for a binary file, I can write this: buf_size=1024*64 # this is an important size... with open(file, "rb") as f: while True: data=f.read(buf_size) if not data: break # deal with the data.... With a text file that I want to read line-by-line, I can write this: with open(file, "r") as file: for line in file: # deal with each line.... Which is shorthand for: with open(file, "r") as file: for line in iter(file.readline, ""): # deal with each line.... This idiom is documented in PEP 234 but I have failed to locate a similar idiom for binary files. I have tried this: >>> with open('dups.txt','rb') as f: ... for chunk in iter(f.read,''): ... i+=1 >>> i 1 # 30 MB file, i==1 means read in one go... I tried putting iter(f.read(buf_size),'') but that is a syntax error because of the parens after the callable in iter(). I know I could write a function, but is there way with the default idiom of for chunk in file: where I can use a buffer size versus a line oriented? Thanks for putting up with the Python newbie trying to write his first non-trivial and idiomatic Python script.

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• Problem detaching entire object graph in GAE-J with JDO

  - by tempy

  I am trying to load the full object graph for User, which contains a collection of decks, which then contains a collection of cards, as such: User: @PersistenceCapable(detachable = "true") @Inheritance(strategy = InheritanceStrategy.SUBCLASS_TABLE) @FetchGroup(name = "decks", members = { @Persistent(name = "_Decks") }) public abstract class User { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) protected Key _ID; @Persistent protected String _UniqueIdentifier; @Persistent(mappedBy = "_Owner") @Element(dependent = "true") protected Set<Deck> _Decks; protected User() { } } Each Deck has a collection of Cards, as such: @PersistenceCapable(detachable = "true") @FetchGroup(name = "cards", members = { @Persistent(name = "_Cards") }) public class Deck { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key _ID; @Persistent String _Name; @Persistent(mappedBy = "_Parent") @Element(dependent = "true") private Set<Card> _Cards = new HashSet<Card>(); @Persistent private Set<String> _Tags = new HashSet<String>(); @Persistent private User _Owner; } And finally, each card: @PersistenceCapable public class Card { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key _ID; @Persistent private Text _Question; @Persistent private Text _Answer; @Persistent private Deck _Parent; } I am trying to retrieve and then detach the entire object graph. I can see in the debugger that it loads fine, but then when I get to detaching, I can't make anything beyond the User object load. (No Decks, no Cards). At first I tried without a transaction to simply "touch" all the fields on the attached object before detaching, but that didn't help. Then I tried adding everything to the default fetch group, but that just generated warnings about GAE not supporting joins. I tried setting the fetch plan's max fetch depth to -1, but that didn't do it. Finally, I tried using FetchGroups as you can see above, and then retrieving with the following code: PersistenceManager pm = _pmf.getPersistenceManager(); pm.setDetachAllOnCommit(true); pm.getFetchPlan().setGroup("decks"); pm.getFetchPlan().setGroup("cards"); Transaction tx = pm.currentTransaction(); Query query = null; try { tx.begin(); query = pm.newQuery(GoogleAccountsUser.class); //Subclass of User query.setFilter("_UniqueIdentifier == TheUser"); query.declareParameters("String TheUser"); List<User> results = (List<User>)query.execute(ID); //ID = Supplied parameter //TODO: Test for more than one result and throw if(results.size() == 0) { tx.commit(); return null; } else { User usr = (User)results.get(0); //usr = pm.detachCopy(usr); tx.commit(); return usr; } } finally { query.closeAll(); if (tx.isActive()) { tx.rollback(); } pm.close(); } This also doesn't work, and I'm running out of ideas...

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• Linear Interpolation. How to implement this algorithm in C ? (Python version is given)

  - by psihodelia

  There exists one very good linear interpolation method. It performs linear interpolation requiring at most one multiply per output sample. I found its description in a third edition of Understanding DSP by Lyons. This method involves a special hold buffer. Given a number of samples to be inserted between any two input samples, it produces output points using linear interpolation. Here, I have rewritten this algorithm using Python: temp1, temp2 = 0, 0 iL = 1.0 / L for i in x: hold = [i-temp1] * L temp1 = i for j in hold: temp2 += j y.append(temp2 *iL) where x contains input samples, L is a number of points to be inserted, y will contain output samples. My question is how to implement such algorithm in ANSI C in a most effective way, e.g. is it possible to avoid the second loop? NOTE: presented Python code is just to understand how this algorithm works. UPDATE: here is an example how it works in Python: x=[] y=[] hold=[] num_points=20 points_inbetween = 2 temp1,temp2=0,0 for i in range(num_points): x.append( sin(i*2.0*pi * 0.1) ) L = points_inbetween iL = 1.0/L for i in x: hold = [i-temp1] * L temp1 = i for j in hold: temp2 += j y.append(temp2 * iL) Let's say x=[.... 10, 20, 30 ....]. Then, if L=1, it will produce [... 10, 15, 20, 25, 30 ...]

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• Is False == 0 and True == 1 in Python an implementation detail or guaranteed by the language?

  - by EOL

  Is it guaranteed that False == 0 and True == 1, in Python? For instance, is it in any way guaranteed that the following code will always produce the same results, whatever the version of Python (existing and in the foreseeable future)? 0 == False # True 1 == True # True ['zero', 'one'][False] # is 'zero' Any reference to the official documentation would be much appreciated! Other comments would be appreciated too… :) Edit: As noted in many answers, bool inherits from int. The question can therefore be recast as: "Is this an implementation detail that might change in the future, or does the documentation officially say that programmers can rely on booleans inheriting from integers?". This question is relevant for writing robust code that won't fail because of implementation details! Edit 2: The original question is still open, I believe (even though I accepted what I thought was the closest answer): even though Python 3 officially recognizes booleans as integers, I have not yet seen any official integer values for False and True… It therefore looks to me like it is best to stay clear from the assumption that False==0 and True==1.

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• Noob-Ready Cython Tutorials

  - by spearfire

  I know a bunch of scripting languages, (python, ruby, lua, php) but I don't know any compiled languages like C/C++ , I wanted to try and speed up some python code using cython, which is essentially a python - C compiler, aimed at creating C extensions for python. Basically you code in a stricter version of python which compiles into C - native code. here's the problem, I don't know C, yet the cython documentation is aimed at people who obviously already know C (nothing is explained, only presented), and is of no help to me, I need to know if there are any good cython tutorials aimed at python programmers, or if I'm gonna have to learn C before I learn Cython. bear in mind I'm a competent python programmer, i would much rather learn cython from the perspective of the language I'm already good at, rather than learn a whole new language in order to learn cython. 1) PLEASE don't recommend psyco edit: ANY information that will help understand the oficial cython docs is useful information

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• Facebook publish HTTP Error 400 : bad request

  - by Abhishek

  Hey I am trying to publish a score to Facebook through python's urllib2 library. import urllib2,urllib url = "https://graph.facebook.com/USER_ID/scores" data = {} data['score']=SCORE data['access_token']='APP_ACCESS_TOKEN' data_encode = urllib.urlencode(data) request = urllib2.Request(url, data_encode) response = urllib2.urlopen(request) responseAsString = response.read() I am getting this error: response = urllib2.urlopen(request) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib2.py", line 124, in urlopen return _opener.open(url, data, timeout) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib2.py", line 389, in open response = meth(req, response) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib2.py", line 502, in http_response 'http', request, response, code, msg, hdrs) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib2.py", line 427, in error return self._call_chain(*args) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib2.py", line 361, in _call_chain result = func(*args) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib2.py", line 510, in http_error_default raise HTTPError(req.get_full_url(), code, msg, hdrs, fp) urllib2.HTTPError: HTTP Error 400: Bad Request Not sure if this is relating to Facebook's Open Graph or improper urllib2 API use.

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• Cython Speed Boost vs. Usability

  - by zubin71

  I just came across Cython, while I was looking out for ways to optimize Python code. I read various posts on stackoverflow, the python wiki and read the article "General Rules for Optimization". Cython is something which grasps my interest the most; instead of writing C-code for yourself, you can choose to have other datatypes in your python code itself. Here is a silly test i tried, #!/usr/bin/python # test.pyx def test(value): for i in xrange(value): i**2 if(i==1000000): print i test(10000001) $ time python test.pyx real 0m16.774s user 0m16.745s sys 0m0.024s $ time cython test.pyx real 0m0.513s user 0m0.196s sys 0m0.052s Now, honestly, i`m dumbfounded. The code which I have used here is pure python code, and all I have changed is the interpreter. In this case, if cython is this good, then why do people still use the traditional Python interpretor? Are there any reliability issues for Cython?

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• WxPython Incompatible With Snow Leopard?

  - by Alex

  Hello all, Recently I upgraded to Snow Leopard, and now I can't run programs built with wxPython. The errors I get are (from Eclipse + PyDev): import wx File "/var/tmp/wxWidgets/wxWidgets-13~231/2.6/DSTROOT/System/Library/Frameworks /Python.framework/Versions/2.6/Extras/lib/ python/wx-2.8-mac-unicode/wx/__init__.py", line 45, in <module> File "/var/tmp/wxWidgets/wxWidgets-13~231/2.6/DSTROOT /System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib /python/wx-2.8-mac-unicode/wx/_core.py", line 4, in <module> ImportError:/System/Library/Frameworks /Python.framework/Versions/2.6/Extras/lib/python /wx-2.8-mac-unicode/wx/_core_.so: no appropriate 64-bit architecture (see "man python" for running in 32-bit mode) I don't really understand them and would appreciate if you could help me to do so, also, if you do know what's going on, how can I go about fixing them? Maybe this has something to do with the fact that Snow Leopard is 64-bit? Thanks!!

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• Interpreted vs. Compiled vs. Late-Binding

  - by zubin71

  Python is compiled into an intermediate bytecode(pyc) and then executed. So, there is a compilation followed by interpretation. However, long-time Python users say that Python is a "late-binding" language and that it should`nt be referred to as an interpreted language. How would Python be different from another interpreted language? Could you tell me what "late-binding" means, in the Python context? Java is another language which first has source code compiled into bytecode and then interpreted into bytecode. Is Java an interpreted/compiled language? How is it different from Python in terms of compilation/execution? Java is said to not have, "late-binding". Does this have anything to do with Java programs being slighly faster than Python? Itd be great if you could also give me links to places where people have already discussed this; id love to read more on this. Thank you.

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