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• Why are C, C++, and LISP so prevalent in embedded devices and robots?

  - by David

  It seems that the software language skills most sought for embedded devices and robots are C, C++, and LISP. Why haven't more recent languages made inroads into these applications? For example, Erlang would seem particularly well-suited to robotic applications, since it makes concurrent programming easier and allows hot swapping of code. Python would seem to be useful, if for no other reason than its support of multiple programming paradigms. I'm even surprised that Java hasn't made a foray into general robotic programming. I'm sure one argument would be, "Some newer languages are interpreted, not compiled" - implying that compiled languages are quicker and use fewer computational resources. Is this still the case, in a time when we can put a Java Virtual Machine on a cell phone or a SunSpot? (and isn't LISP interpreted anyway?)

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• Why doesn't functools.partial return a real function (and how to create one that does)?

  - by epsilon

  So I was playing around with currying functions in Python and one of the things that I noticed was that functools.partial returns a partial object rather than an actual function. One of the things that annoyed me about this was that if I did something along the lines of: five = partial(len, 'hello') five('something') then we get TypeError: len() takes exactly 1 argument (2 given) but what I want to happen is TypeError: five() takes no arguments (1 given) Is there a clean way to make it work like this? I wrote a workaround, but it's too hacky for my taste (doesn't work yet for functions with varargs): def mypartial(f, *args): argcount = f.func_code.co_argcount - len(args) params = ''.join('a' + str(i) + ',' for i in xrange(argcount)) code = ''' def func(f, args): def %s(%s): return f(*(args+(%s))) return %s ''' % (f.func_name, params, params, f.func_name) exec code in locals() return func(f, args)

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• Can I use Blender to create 3D wall image viewer application under Linux?

  - by sgon00

  Hi, Is that possible to use Blender to create Cooliris-like 3D wall image viewer application under Linux? I don't see many people use Blender (BGE) to create desktop application, so I am wondering if this is possible. People normally use Blender for modeling/movie and game engine. I can not find a good way to create 3D application in Linux so far. I was thinking about pyQT+opengl. But I feel that is hard to do. No robust and easy-to-use qt+opengl toolkit available from my research. I know a little bit of Blender, that's why I am asking if Blender is an alternative solution. (python is preferred) The image viewer doesn't have to be windowed. It can be full screen, like a game?. I would like to add many cool effects into this application. Hopefully cooler than Cooliris which is written in flash. Thanks a lot.

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• Opinions about Dabo

  - by driverate

  Has anyone used Dabo lately? How does it rate vs Boa Constructor, etc? I'm writing a new Python database app and Dabo looks promising, but what's the real-world scoop on it? Is it used by many developers? It's not talked about very much here on SO, or anywhere, as far as I can tell. I'm just a little concerned that the support community might be too small, or the possibility that writers might decide to throw in the towel. What is your assessment of Dabo?

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• Numeric GUI bottleneck

  - by Physic

  Hi all, I've made a GUI to set up and start a numerical integrator using PyQT4, Wing, QT, and Python 2.6.6, on my Mac. The thing is, when I run the integrator form the GUI, it takes very many times longer than when I crudely run the integrator from the command line. As an example, a 1000 year integration took 98 seconds on the command line and ~570 seconds from the GUI. In the GUI, the integration runs from a thread and then returns. It uses a a queue to communicate back to the GUI. Does anyone have any ideas as to where the bottleneck is? I suspect that others may be experiencing something like this just on a smaller scale. t = threading.Thread( target=self.threadsafe_start_thread, args=( self.queue, self.selected ) ) t.start() Thanks!

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• super(type,subclass) in simple singleton implementation

  - by Tianchen Wu

  when I was implementing naive singleton in python, I came up with a problem with super key word. As usual the behavior of super is always tricky and buggy, hope someone can shed light on it. Thanks :) The problem is that: class Singleton(object): def __new__(cls,*args,**kw): if not hasattr(cls,'_instance'): #create a instance of type cls, origin=super(Singleton,Singleton).__new__(cls,*args,**kw) cls._instance=origin return cls._instance class B(Singleton): def __init__(self,b): self.b=b It actually works, but I am wondering Will it be better if I change line 5 to the below, like in most of the books? origin=super(Singleton,cls).__new__(cls,*args,**ks) what's the difference to make?

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• "Introduction to Computer Science and Programming" for a beginner.

  - by Richard

  Hi everyone! Im new here and also new to developing software and programming, and with new I mean 0 experience or schooling for it. As Im currently studying medicine via internet and I use a computer on an average of about 8-9 hours a day, this has lead me to get very interested in programming. I got a link from a fellow Redditor and I got some questions before I dive into this project. http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-00Fall-2008/CourseHome/index.htm Is this too much/hard for a beginner? Is Python™ programming language the way to go or would I be better off learning some other kind of language to begin with? What other ways of learning basic programming by myself is there? Are there any better ways for a complete beginner to start off? Thank you for your time!

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• OpenID login on local development server for google app engine

  - by Alex Jeffery

  Are you able to use open id to log into the local development server with google app engine sdk version 1.4.1 and python 2.5? When I execute this self.redirect(users.create_login_url(continue_url, None, openid_url)) I get redirected to http://localhost/_ah/login rather than the openid url. The openid url and continue url are valid. My app.yaml looks like this - url: /_ah/login_required script: do_openid_login.py - url: /users/(.*) script: routers/user_router.py login: required If I browse to http://localhost/users/ I am also redirected to http://localhost/_ah/login rather than http://localhost/_ah/login_required Is there a config issue or does openid not work locally?

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• Efficiently Reshaping/Reordering Numpy Array to Properly Ordered Tiles (Image)

  - by Phelix

  I would like to be able to somehow reorder a numpy array for efficient processing of tiles. what I got: >>> A = np.array([[1,2],[3,4]]).repeat(2,0).repeat(2,1) >>> A # image like array array([[[1, 1, 2, 2], [1, 1, 2, 2]], [[3, 3, 4, 4], [3, 3, 4, 4]]]) >>> A.reshape(2,2,4) array([[[1, 1, 2, 2], [1, 1, 2, 2]], [[3, 3, 4, 4], [3, 3, 4, 4]]]) what I want: X >>> X array([[[1, 1, 1, 1], [2, 2, 2, 2]], [[3, 3, 3, 3], [4, 4, 4, 4]]]) to be able to do something like: >>> X[X.sum(2)>12] -= 1 >>> X array([[[1, 1, 1, 1], [2, 2, 2, 2]], [[3, 3, 3, 3], [3, 3, 3, 3]]]) Is this possible without a slow python loop? Bonus: Conversion back from X to A Edit: How can I get X from A?

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• AppEngine and Django: including a template file

  - by PythonPower

  As the title suggests, I'm using Google App Engine and Django. I have quite a bit of identical code across my templates and would like to reduce this by including template files. So, in my main application directory I have the python handler file, the main template, and the template I want to include in my main template. I would have thought that including {% include "fileToInclude.html" %} would work on its own but that simply doesn't include anything. I assume I have to set something up, maybe using TEMPLATE_DIRS, but can't figure it out on my own. EDIT: I've tried: TEMPLATE_DIRS = (os.path.join(os.path.dirname(__file__), 'templates'), ) But to no avail. I'll try some other possibilities too.

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• parse this directory path without losing slash

  - by PPTim

  hi, I have a wxPython application. I am taking in a directory path from a textbox using GetValue(). I notice that while trying to parse in the directory path "C:\Documents and Settings\UserName\Desktop\InputFile.xls", python sees the string as 'C:\\Documents and Settings\UserName\\Desktop\\InputFile.xls' (missing a slash between "Settings" and "UserName). Why is it that only that slash is not correctly escaped? Once the string has been changed to 'C:\Documents and Settings\UserName\Desktop\InputFile.xls', is there a type conversion or function that can does this properly? Thanks.

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• How do I do import hooks in IronPython/Silverlight?

  - by ahlatimer

  I'm extending TryPython to (along with various other things) allow users to save a file and subsequently import that file. TryPython overloads the built in file operations, so I need to know what parts of import need to hooked into in order for import to use the overloaded file operations. Really, a basic overview of IronPython's import when used in Silverlight would be extremely helpful. I don't need a complete working solution (although I won't stop you from writing one! :). I'm a Python newbie, and I really have no idea where to even begin. Thanks!

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• how to exit recursive math formula and still get an answer

  - by calccrypto

  i wrote this python code, which from wolfram alpha says that its supposed to return the factorial of any positive value (i probably messed up somewhere), integer or not: from math import * def double_factorial(n): if int(n) == n: n = int(n) if [0,1].__contains__(n): return 1 a = (n&1) + 2 b = 1 while a<=n: b*=a a+= 2 return float(b) else: return factorials(n/2) * 2**(n/2) *(pi/2)**(.25 *(-1+cos(n * pi))) def factorials(n): return pi**(.5 * sin(n*pi)**2) * 2**(-n + .25 * (-1 + cos(2*n*pi))) * double_factorial(2*n) the problem is , say i input pi to 6 decimal places. 2*n will not become a float with 0 as its decimals any time soon, so the equation turns out to be pi**(.5 * sin(n*pi)**2) * 2**(-n + .25 * (-1 + cos(2*n*pi))) * double_factorial(loop(loop(loop(...))))) how would i stop the recursion and still get the answer? ive had suggestions to add an index to the definitions or something, but the problem is, if the code stops when it reaches an index, there is still no answer to put back into the previous "nests" or whatever you call them

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• How to control utf-8 string paddings

  - by Kev

  I got three UTF-8 stings: hello, world hello, ?? hello, ?rld I only want the first 10 chars so that the bracket in one column: [hello, wor] [hello, ? ] [hello, ?r] In console: width('??')==width('worl') width('? ')==width('wor') #a white space behind '?' python's format() doesn't help when UTF-8 chars mixed in >>> for s in ['[{0:<{1}.{1}}]'.format(s, 10) for s in ['hello, world', 'hello, ??', 'hello, ?rld']]: ... print(s) ... [hello, wor] [hello, ?? ] [hello, ?rl] So, I wonder if there is a standard way to do the UTF-8 padding staff?

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• Same question to multiple remote users with different login

  - by user562802

  Hello all, This is my first post to Stack Overflow so apologies if I chosen wrong words for the title. I am very new to Google App Engine and python. I am building a web application using Pyhton and Django which is question and multiple answers type. Once the users are login to website,they will be provided with random questions from datastore. What my requirement is if certain users want to form group so that they all can get the same set of random questions to answer,is this possible ? Without forming the group each user are getting different random questions on their end. Thanks, Sunil

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• Protobuf compiler for several languages

  - by Stipa

  Hi, In my project I have components written on Python, ObjectiveC and J2ME. I want to use protobuf as data interchange format. However, there are one issue I need to resolve. Google implementation doesn't support ObjC and J2ME. There are 3rd party implementations that supports those languages. But I really don't want to be depended of several protoc implementations. What is the best way for me to have protobufs for several languages? Do I need to use different compilers or there is other option? Thanks, -Lev

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• Storing task state between multiple django processes

  - by user366148

  I am building a logging-bridge between rabbitmq messages and Django application to store background task state in the database for further investigation/review, also to make it possible to re-publish tasks via the Django admin interface. I guess it's nothing fancy, just a standard Producer-Consumer pattern. Web application publishes to message queue and inserts initial task state into the database Consumer, which is a separate python process, handles the message and updates the task state depending on task output The problem is, some tasks are missing in the db and therefore never executed. I suspect it's because Consumer receives the message earlier than db commit is performed. So basically, returning from Model.save() doesn't mean the transaction has ended and the whole communication breaks. Is there any way I could fix this? Maybe some kind of post_transaction signal I could use? Thank you in advance.

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• mutliprocessing.Pool.add_sync() eating up memory

  - by Austin

  I want to use multithreading to make my script faster... I'm still new to this. The Python doc assumes you already understand threading and what-not. So... I have code that looks like this from itertools import izip from multiprocessing import Pool p = Pool() for i, j in izip(hugeseta, hugesetb): p.apply_async(number_crunching, (i, j)) Which gives me great speed! However, hugeseta and hugesetb are really huge. Pool keeps all of the _i_s and _j_s in memory after they've finished their job (basically, print output to stdout). Is there any to del i, and j after they complete?

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• How to improve the speed of a loop containing a sqlalchemy query statement as conditional

  - by LtPinback

  This loop checks if a record is in the sqlite database and builds a list of dictionaries for those records that are missing and then executes a multiple insert statement with the list. This works but it is very slow (at least i think it is slow) as it takes 5 minutes to loop over 3500 queries. I am a complete newbie in python, sqlite and sqlalchemy so I wonder if there is a faster way of doing this. list_dict = [] session = Session() for data in data_list: if session.query(Class_object).filter(Class_object.column_name_01 == data[2]).filter(Class_object.column_name_00 == an_id).count() == 0: list_dict.append({'column_name_00':a_id, 'column_name_01':data[2]}) conn = engine.connect() conn.execute(prices.insert(),list_dict) conn.close() session.close() edit: I moved session = Session() outside the loop. Did not make a difference.

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• Best way to parse XMPP-like XML streams?

  - by codethief

  I am working on a server application which receives data over a TCP socket in an XMPP-like XML format, i.e. every child of the <root> element essentially represents one separate request (stanza). The connection is closed as soon as </root> is received. I do know that I must use a stream parser like SAX, somehow. Though, for convenience, I'd prefer to have a tree-like interface to access each stanza's child elements. (The data sent with every request is not large so I think it makes sense to read each stanza as a whole.) What's the best way to realize that in Python (preferably v3)? This is the code I'd like to build it in. Feel free to point me in a totally different direction to solve this issue. import socketserver import settings class MyServer(socketserver.ThreadingMixIn, socketserver.TCPServer): pass class MyRequestHandler(socketserver.StreamRequestHandler): def handle(self): pass if __name__ == '__main__': server = MyServer((settings.host, settings.port), MyRequestHandler) server.serve_forever()

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• which language to choose for a LIVE web application?

  - by fayer

  i want to create not only a web application, but a web application where everything is LIVE. eg. if someone posts a message and then another one replies, then the creator will get on his webpage a notification. and also i want to implement a chat in the web application. i want these features to be implemented using true server-push (no javascript polling)! because i only want to create web applications i don't think i will use java. i wonder if i should use python, ruby or php for this? thanks

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• Throw blank even-numbered/left pages

  - by TimGJ

  I am trying to typeset a large document using ReportLab and Python 2.7. It has a number of sections (about 6 in a 1,000 page document) and I would like each to start on odd-numbered/right-hand page. I have no idea though whether the preceding page will be odd or even and so need the ability to optionally throw an additional blank page before a particular paragraph style (like you sometimes get in manuals where some pages are "intentionally left blank"). Can anyone suggest how this could be done, as the only conditional page break I can find works on the basis of the amount of text on the page not a page number. I also need to make sure that the blank page is included in the PDF so that double-sided printing works.

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• Hadoop Map Reduce job never finishes

  - by rohanbk

  I am running a Hadoop Map Reduce job using a Python Mapper and Reducer script, and Hadoop Streaming. Both my Map and Reduce jobs run till they are both 100%, but the job doesn't end. I know that when things go sour, Hadoop will terminate the job, but in this case, both stages reach a 100% and just never end. Has anyone else encountered anything similar? Also, how do I debug my program to figure out where things are going wrong? If I use a smaller input file, and I just run something like: $> cat input_file | mapper.py | sort | reduce.py >> output_file everything works perfectly fine. However, when I use Hadoop, things don't work out.

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• Getting service unavailable message when sending messages to google xmpp using wokkel

  - by Code freak

  Hi, I made a wokkel (twisted python) bot to send and receive messages from the google xmpp service. Everything (auth, presence) etc works fine. One of the rquirements of our prject is that we need to send broadcast messages to everyone in the list. Normal messages and replies work fin, but when i snd a broadcast message, i get this service unavailable error 503 message. There are about 1000 user in my contact list. Is this some bug in the code or is it google policy to prevent rapid messaging. Also, how do other google bots cater to a large contact base ? does google provide a commercial solution for such applications ? Thanks

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• If a command line program is unsure of stdout's encoding, what encoding should it output?

  - by mackstann

  I have a command line program written in Python, and when I pipe it through another program on the command line, sys.stdout.encoding is None. This makes sense, I suppose -- the output could be another program, or a file you're redirecting it into, or whatever, and it doesn't know what encoding is desired. But neither do I! This program will be used by many different people (humor me) in different ways. Should I play it safe and output only ascii (replacing non-ascii chars with question marks)? Or should I output UTF-8, since it's so widespread these days?

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