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• Standardizing camera input in OpenCV? (Contrast/Saturation/Brightness etc..)

  - by karpathy

  I am building an application using OpenCV that uses the webcam and runs some vision algorithms. I would like to make this application available on the internet after I am done, but I am concerned about the vast differences in camera settings on every computer, and I am worried that the algorithm may break if the settings are too different from mine. Is there any way, after capturing the frame, to post process it and make sure that the contrast is X, brightness is Y, and saturation is Z? I think the Camera settings themselves can not be changed from code directly using the current OpenCV Python bindings. Would anyone be able to tell me about how I could calculate some of these parameters from the image and adjust them appropriately using OpenCV?

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• Erlang message loops

  - by Roger Alsing

  How does message loops in erlang work, are they sync when it comes to processing messages? As far as I understand, the loop will start by "receive"ing a message and then perform something and hit another iteration of the loop. So that has to be sync? right? If multiple clients send messages to the same message loop, then all those messages are queued and performed one after another, or? To process multiple messages in parallell, you would have to spawn multiple message loops in different processes, right? Or did I misunderstand all of it?

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• Why does concatenating a boolean value return an integer?

  - by joshhunt

  In python, you can concatenate boolean values, and it would return an integer. Example: >>> True True >>> True + True 2 >>> True + False 1 >>> True + True + True 3 >>> True + True + False 2 >>> False + False 0 Why? Why does this make sense? I understand that True is often represented as 1, whereas False is represented as 0, but that still does not explain how adding two values together of the same type returns a completely different type.

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• How can I merge two Linq IEnumerable<T> queries without running them?

  - by makerofthings7

  How do I merge a List<T> of TPL-based tasks for later execution? public async IEnumerable<Task<string>> CreateTasks(){ /* stuff*/ } My assumption is .Concat() but that doesn't seem to work: void MainTestApp() // Full sample available upon request. { List<string> nothingList = new List<string>(); nothingList.Add("whatever"); cts = new CancellationTokenSource(); delayedExecution = from str in nothingList select AccessTheWebAsync("", cts.Token); delayedExecution2 = from str in nothingList select AccessTheWebAsync("1", cts.Token); delayedExecution = delayedExecution.Concat(delayedExecution2); } /// SNIP async Task AccessTheWebAsync(string nothing, CancellationToken ct) { // return a Task } I want to make sure that this won't spawn any task or evaluate anything. In fact, I suppose I'm asking "what logically executes an IQueryable to something that returns data"? Background Since I'm doing recursion and I don't want to execute this until the correct time, what is the correct way to merge the results if called multiple times? If it matters I'm thinking of running this command to launch all the tasks var AllRunningDataTasks = results.ToList(); followed by this code: while (AllRunningDataTasks.Count > 0) { // Identify the first task that completes. Task<TableResult> firstFinishedTask = await Task.WhenAny(AllRunningDataTasks); // ***Remove the selected task from the list so that you don't // process it more than once. AllRunningDataTasks.Remove(firstFinishedTask); // TODO: Await the completed task. var taskOfTableResult = await firstFinishedTask; // Todo: (doen't work) TrustState thisState = (TrustState)firstFinishedTask.AsyncState; // TODO: Update the concurrent dictionary with data // thisState.QueryStartPoint + thisState.ThingToSearchFor Interlocked.Decrement(ref thisState.RunningDirectQueries); Interlocked.Increment(ref thisState.CompletedDirectQueries); if (thisState.RunningDirectQueries == 0) { thisState.TimeCompleted = DateTime.UtcNow; } }

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• Windows Azure: Parallelization of the code

  - by veda

  I have some matrix multiplication operation. I want to parallelize the execution of those operations through multiple processors.. This can be done on high performance computing cluster using MPI (Message Passing Interface). Like wise, can I do some parallelization in the cloud using multiple worker roles. Is there any means for doing that.

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• How to add http headers in suds 0.3.6?

  - by Esabe

  Hi everyone, I have an application in python 2.5 which sends data through suds 0.3.6. The problem is that the data contains non-ascii characters, so I need the following header to exist in the soap message: Content-Type="text/html; charset="utf-8" and the header that exists in the SOAP message is just: Content-Type="text/html" I know that it is fixed in suds 0.4, but it requires Python2.6 and I NEED Python2.5 because I use CentOS and it needs that version. So the question is: How could I change or add new HTTP headers to a SOAP message?

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• how to add markup to text using JavaScript regex

  - by Richard

  I need to add markup to some text using JavaScript regular expressions. In Python I could do this with: >>> import re >>> re.sub('(banana|apple)', r'<b>{\1}</b>', 'I have 1 banana and 2 apples!') 'I have 1 <b>{banana}</b> and 2 <b>{apple}</b>s!' What is the equivalent in JavaScript? string.replace(regex, newstring) seems to only take a raw string for replacing.

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• Create event for another owner using Facebook Graph API

  - by David

  Hi, I'm at the moment working on a web page where the users who visit it should have the possibility to create an event in my web page's name. There is a Page on Facebook for the web page which should be the owner of the user created event. Is this possible? All users are authenticated using Facebook Connect, but since the event won't be created in their name I don't know if that's so much of help. The Python SDK will be used since the event shall be implemented server side. / D

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• Halting Django's dev server via page request?

  - by Ben Blank

  I'm looking at writing a portable, light-weight Python app. As the "GUI toolkit" I'm most familiar with — by a wide margin! — is HTML/CSS/JS, I thought to use Django as a framework for the project, using its built-in "development server" (manage.py runserver). I've been banging on a proof-of-concept for a couple hours and the only real problem I've encountered so far is shutting down the server once the user has finished using the app. Ideally, I'd like there to be a link on the app's pages which shuts down the server and closes the page, but nothing I see in the Django docs suggests this is possible. Can this be done? For that matter, is this a reasonable approach for writing a small, portable GUI tool?

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• How do I make an already written concurrent program run on a GPU array?

  - by memius

  I have a neural network written in Erlang, and I just bought a GeForce GTX 260 card with a 240 core GPU on it. Is it trivial to use CUDA as glue to run this on the graphics card?

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• Subdomain forwarding using .htaccess

  - by RJ

  I want to redirect a praticular subdomain to the main domain http(s)://dl.example.com/par1/par2 to http(s)://www.example.com/par1/par2 How to achieve the above using .htaccess Why i want to do this: Whenever any user download a file from my server, if the file is huge , then user cannot do any other operation until the file is downloaded completely...so the solution that i have thought is to forward the download request through subdomain so that the browser may continue with rest of the operation. Thanks

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• What are some good ways to do intermachine locking?

  - by mike

  Our server cluster consists of 20 machines, each with 10 pids of 5 threads. We'd like some way to prevent any two threads, in any pid, on any machine, from modifying the same object at the same time. Our code's written in Python and runs on Linux, if that helps narrow things down. Also, it's a pretty rare case that two such threads want to do this, so we'd prefer something that optimizes the "only one thread needs this object" case to be really fast, even if it means that the "one thread has locked this object and another one needs it" case isn't great. What are some of the best practices?

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• Extract string that is delimited with constant and ends with two numbers (numbers have to be included)

  - by Edmon

  I have a text that contains string of a following structure: text I do not care about, persons name followed by two IDs. I know that: a person's name is always preceded by XYZ code and that is always followed by two, space separated numbers. Name is not always just a last name and first name. It can be multiple last or first names (think Latin american names). So, I am looking to extract string that follows the constant XYZ code and that is always terminated by two separate numbers. You can say that my delimiter is XYZ and two numbers, but numbers need to be part of the extracted value as well. From blah, blah XYZ names, names 122322 344322 blah blah I want to extract: names, names 122322 344322 Would someone please advise on the regular expression for this that would work with Python's re package.

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• MPI Large Data all to all transfer

  - by csslayer

  My application of MPI has some process that generate some large data. Say we have N+1 process (one for master control, others are workers), each of worker processes generate large data, which is now simply write to normal file, named file1, file2, ..., fileN. The size of each file may be quite different. Now I need to send all fileM to rank M process to do the next job, So it's just like all to all data transfer. My problem is how should I use MPI API to send these files efficiently? I used to use windows share folder to transfer these before, but I think it's not a good idea. I have think about MPI_file and MPI_All_to_all, but these functions seems not to be so suitable for my case. Simple MPI_Send and MPI_Recv seems hard to be used because every process need to transfer large data, and I don't want to use distributed file system for now.

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• Downsampling the number of entries in a list (without interpolation)

  - by Dave

  I have a Python list with a number of entries, which I need to downsample using either: A maximum number of rows. For example, limiting a list of 1234 entries to 1000. A proportion of the original rows. For example, making the list 1/3 its original length. (I need to be able to do both ways, but only one is used at a time). I believe that for the maximum number of rows I can just calculate the proportion needed and pass that to the proportional downsizer: def downsample_to_max(self, rows, max_rows): return downsample_to_proportion(rows, max_rows / float(len(rows))) ...so I really only need one downsampling function. Any hints, please? EDIT The list contains objects, not numeric values so I do not need to interpolate. Dropping objects is fine.

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• help me understand cuda

  - by scatman

  i am having some troubles understanding threads in NVIDIA gpu architecture with cuda. please could anybody clarify these info: an 8800 gpu has 16 SMs with 8 SPs each. so we have 128 SPs. i was viewing stanford's video presentation and it was saying that every SP is capable of running 96 threads cuncurrently. does this mean that it (SP) can run 96/32=3 warps concurrently? moreover, since every SP can run 96 threads and we have 8 SPs in every SM. does this mean that every SM can run 96*8=768 threads concurrently?? but if every SM can run a single Block at a time, and the maximum number of threads in a block is 512, so what is the purpose of running 768 threads concurrently and have a max of 512 threads? a more general question is:how are blocks,threads,and warps distributed to SMs and SPs? i read that every SM gets a single block to execute at a time and threads in a block is divided into warps (32 threads), and SPs execute warps.

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• Text-based one-on-one chat with Flash interface: what to power the backend?

  - by Zachary Burt

  Hey guys. I'm building a website where I hook people up so that they can anonymously vent to strangers. You either choose to be a listener, or a talker, and then you get catapulted into a one-on-one chat room. The reason for the app's construction is because you often can't vent to friends, because your deepest vulnerabilities can often be leveraged against you later on. (Like it or not, this is a part of human nature. Sad.) I'm looking for some insight into how I should architect everything. I found this neat tutorial, http://giantflyingsaucer.com/blog/?p=875, which suggests using python & stackless + flash. Someone else suggested I should try using p2p sockets, but I don't even know where to begin to look for info on that. Any other suggestions? I'd like to keep it simple. :^)

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• Recalling import in module

  - by Isaiah

  I'm still learning python and after playing around with pygame I noticed I'm re-importing things in modules I'm importing that I've already imported. import pygame For instance I have some classes in a separate file, but I must also import pygame into that file too for them to work. Does it actually import the code twice? Will it slow down my program? Or does it just pull the same import from before, but if it does that, why would I need to import it? Is there anything like (load) in lisp that just pulls in the code like it is part of the main file? Thank You

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• Parallelizing a serial algorithm

  - by user643813

  Hej folks, I am working on porting a Text mining/Natural language application from single-core to a Map-Reduce style system. One of the steps involves a while loop similar to this: Queue<Element>; while (!queue.empty()) { Element e = queue.next(); Set<Element> result = calculateResultSet(e); if (!result.empty()) { queue.addAll(result); } } Each iteration depends on the result of the one before (kind of). There is no way of determining the number of iterations this loop will have to perform. Is there a way of parallelizing a serial algorithm such as this one? I am trying to think of a feedback mechanism, that is able to provide its own input, but how would one go about parallelizing it? Thanks for any help/remarks

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• Making a video with opencv and ffmpeg. How to find the right color format?

  - by luc

  I have a webcam video recorder program built with python, opencv and ffmpeg It works ok except that the color of the video is more blue than the reality. The problem seems to come from color format of images. It seems that OpenCv is giving BGR images and ffmpeg+libx264 is expecting YUV420p. I've read that YUV420p correspond to YCbCr. opencv has no conversion from BGR to YCbCr. It only has a conversion to YCrCb. I have made some searchs and tried different alternatives to try converting opencv image to something that could be ok for ffmpeg+libx264. None is working. At this point, I am a bit lost and I would appreciate any pointer that could help me to fix this color issue.

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• Counting vowels in a string using recursion

  - by Daniel Love Jr

  In my python class we are learning about recursion. I understand that it's when a function calls itself, however for this particular assignment I can't figure out how exactly to get my function to call it self to get the desired results. I need to simply count the vowels in the string given to the function. def recVowelCount(s): 'return the number of vowels in s using a recursive computation' vowelcount = 0 vowels = "aEiou".lower() if s[0] in vowels: vowelcount += 1 else: ??? I'm really not sure where to go with this, it's quite frustrating. I came up with this in the end, thanks to some insight from here. def recVowelCount(s): 'return the number of vowels in s using a recursive computation' vowels = "aeiouAEIOU" if s == "": return 0 elif s[0] in vowels: return 1 + recVowelCount(s[1:]) else: return 0 + recVowelCount(s[1:])

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• add uchar values in ushort array with sse2 or sse3

  - by pompolus

  i have an unsigned short dst[16][16] matrix and a larger unsigned char src[m][n] matrix. Now i have to access in the src matrix and add a 16x16 submatrix to dst, using sse2 or ss3. In a my older implementation, I was sure that my summed values ??were never greater than 256, so i could do this: for (int row = 0; row < 16; ++row) { __m128i subMat = _mm_lddqu_si128(reinterpret_cast<const __m128i*>(src)); dst[row] = _mm_add_epi8(dst[row], subMat); src += W; // Step to next row i need to add } where W is an offset to reach the desired rows. This code works, but now my values in src are larger and summed could be greater than 256, so i need to store them as ushort. i've tried this: for (int row = 0; row < 16; ++row) { __m128i subMat = _mm_lddqu_si128(reinterpret_cast<const __m128i*>(src)); dst[row] = _mm_add_epi16(dst[row], subMat); src += W; // Step to next row i need to add } but it doesn't work. I'm not so good with sse, so any help will be appreciated.

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• Error 500 on template.render() with jinja2

  - by Asperitas

  I am working on playing with some Python to create a webapp. At first I put the HTML in a string, using %s to fill certain elements. That all worked perfectly. Now I want to put the HTML in a template, so I followed this tutorial. My code looks like this (I deleted irrelevant code for this error): import codecs import cgi import os import jinja2 jinja_environment = jinja2.Environment(loader=jinja2.FileSystemLoader(os.path.join(os.path.dirname(__file__)))) class Rot13Handler(webapp2.RequestHandler): def get(self): template = jinja_environment.get_template('rot13.html') self.response.out.write(template.render({'text': ''})) When I replace just template.render({'text': ''}) a random string, the program works fine. I did add the latest jinja2 library to my app.yaml, and naturally my rot13.html does exist with the {{ text }} added. So could anyone please help me in the right direction? I don't know why it's going wrong.

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• Conventional Approaches for Passing Data to Back-End?

  - by Calvin

  Hi guys, I'm fairly new to web development, so please pardon the painfully newbie question that's about to follow. My computer science class group and I are developing a web application for class, which is built in Python (under Django) and uses jQuery on the front end. It's primarily an AJAX-ified application, and passing data from the backend to the front end is done through AJAX calls to specific URLs which return JSON. This is probably a stupid question, but what's the conventional approach for passing data in the opposite direction? We don't want to reload the page or anything, so is it an AJAX pass going the other way or something? Thanks in advance for your help!

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• How to set the value of a wx.combobox by posting an event

  - by Adam Fraser

  The code below demonstrates the problem I am running into. I am creating a wx.ComboBox and trying to mimic it's functionality for testing purposes by posting a wxEVT_COMMAND_COMBOBOX_SELECTED event... this event strangely works fine for wx.Choice, but it doesn't do anything to the ComboBox. There doesn't appear to be a different event that I can post to the combobox, but maybe I'm missing something. I'm running this code on Python 2.5 on a Mac OSX 10.5.8 import wx app = wx.PySimpleApp() def on_btn(evt): event = wx.CommandEvent(wx.wxEVT_COMMAND_COMBOBOX_SELECTED,combobox.Id) event.SetEventObject(combobox) event.SetInt(1) event.SetString('bar') combobox.Command(event) app.ProcessPendingEvents() frame = wx.Frame(None) panel = wx.Panel(frame, -1) # This doesn't work combobox = wx.ComboBox(panel, -1, choices=['foo','bar']) # This works #combobox = wx.Choice(panel, -1, choices=['foo','bar']) combobox.SetSelection(0) btn = wx.Button(panel, -1, 'asdf') btn.Bind(wx.EVT_BUTTON, on_btn) sz = wx.BoxSizer() sz.Add(combobox) sz.Add(btn) panel.SetSizer(sz) frame.Show() app.MainLoop()

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