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• Generating code at compile-time using scripts

  - by Manux

  Hello, I would ideally like to be able to add (very repetitive) C/C++ code to my actual code, but at compile time, code which would come from say, the stdout of a python script, the same way one does with macros. For example, let's say I want to have functions that depend on the public attributes of a given class, being able to just write the following in my C++ code would be a blessing: generate_boring_functions(FooBarClass,"FooBarClass.cpp") Is that feasible using conventional means? Or must I hack with Makefiles and temporary source files? Thanks.

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• Where are the function literals c++?

  - by academicRobot

  First of all, maybe literals is not the right term for this concept, but its the closest I could think of (not literals in the sense of functions as first class citizens). The idea is that when you make a conventional function call, it compiles to something like this: callq <immediate address> But if you make a function call using a function pointer, it compiles to something like this: mov <memory location>,%rax callq *%rax Which is all well and good. However, what if I'm writing a template library that requires a callback of some sort with a specified argument list and the user of the library is expected to know what function they want to call at compile time? Then I would like to write my template to accept a function literal as a template parameter. So, similar to template <int int_literal> struct my_template {...};` I'd like to write template <func_literal_t func_literal> struct my_template {...}; and have calls to func_literal within my_template compile to callq <immediate address>. Is there a facility in C++ for this, or a work around to achieve the same effect? If not, why not (e.g. some cataclysmic side effects)? How about C++0x or another language? Solutions that are not portable are fine. Solutions that include the use of member function pointers would be ideal. I'm not particularly interested in being told "You are a <socially unacceptable term for a person of low IQ>, just use function pointers/functors." This is a curiosity based question, and it seems that it might be useful in some (albeit limited) applications. It seems like this should be possible since function names are just placeholders for a (relative) memory address, so why not allow more liberal use (e.g. aliasing) of this placeholder. p.s. I use function pointers and functions objects all the the time and they are great. But this post got me thinking about the don't pay for what you don't use principle in relation to function calls, and it seems like forcing the use of function pointers or similar facility when the function is known at compile time is a violation of this principle, though a small one.

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• What language is better suited for P2P video streaming?

  - by Roman

  I would like to write a Skype like software which allows P2P video/audio streaming. What language is better suited for that? There are several requirements: Software should be easy to install. It should be easy to program. I want to have access to video information. For example to make a face expression recognition on the fly. It should be free. I am thinking of Python and Java. Which one would be better? Or may be there is a third choice which is better? ADDED Flash is an attractive option since users can use their browser in which flash is installed by default and if not, it's easy to install flash. But I do not know if I can have access to video (if I want to do some processing). Moreover, Flash is not free.

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• Making Django ignore string literals

  - by James

  UPDATE: It turns out this is a deeper question than I thought at first glance - the issue is that python is replacing the string literals before they ever get to django. I will do more investigating and update this if I find a solution. I'm using django to work with LaTeX templates for report generation, and am running into a lot of problems with the way Django replaces parts of strings. Specficially, I've run into two problems where I try to insert a variable containing latex code. The first was that it would replace HTML characters, such as the less than symbol, with their HTML codes, which are of course gibberish to a LaTeX interpreter. I fixed this by setting the context to never autoescape, like so: c = Context(inputs) c.autoescape = False However, I still have my second issue, which is that Django replaces string literals with their corresponding characers, so a double backslash becomes \, and \b becomes a backspace. How can I force Django to leave these characters in place, so inputs['variable'] = '{\bf this is code} \\' won't get mangled when I use {{variable}} to reference it in the django template?

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• Django: url and content creation results in 500 and no apache error log entry

  - by user1684082

  If i try to open a created url i get an 500 error. My procedure was: First python manage.py startapp black I added in project/settings.py under INSTALLED_APPS 'black', I added in project/urls.py url(r'^test/', include('black.urls')), Content of black/urls.py is: from django.conf.urls import patterns, url from black import views urlpatterns = patterns('', url(r'^$', views.index, name='index') ) And content of black/views.py: from django.http import HttpResponse def index(request): return HttpResponse("SHOW ME: BLACK") After all i synced the database. I can't see any error in apache-error-log and also not in my posted django files. What could cause this?

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• Counting unique values in a column with a shell script

  - by Lilly Tooner

  Hello. I have a tab delimited file with 5 columns and need to retrieve a count of just the number of unique lines from column 2. I would normally do this with Perl/Python but I am forced to use the shell for this one. I have successfully in the past used *nix uniq function piped to wc but it looks like I am going to have to use awk in here. Any advice would be greatly appreciated. (I have asked a similar question previously about column checks using awk but this is a little different and I wanted to separate it so if someone in the future has this question this will be here) Many many thanks! Lilly

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• How do I escape a string for a shell command in nodejs (V8 Javascript engine)?

  - by Maciek

  In nodejs, the only way to execute external commands is via sys.exec(cmd). I'd like to call an external command and give it data via stdin. In nodejs there does yet not appear to be a way to open a command and then push data to it (only to exec and receive its standard+error outputs), so it appears the only way I've got to do this right now is via a single string command such as: var dangerStr = "bad stuff here"; sys.exec("echo '" + dangerStr + "' | somecommand"); Most answers to questions like this have focused on either regex which doesn't work for me in nodejs (which uses Google's V8 Javascript engine) or native features from other languages like Python. I'd like to escape dangerStr so that it's safe to compose an exec string like the one above. If it helps, dangerStr will contain JSON data.

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• How can I create an ODBC connection to SAS?

  - by Chris B.

  I'm writing a program that needs to access SAS data. I've downloaded the ODBC drivers for SAS and installed them, but I need to be able to create ODBC connections on the fly, programmatically. The following code (in Python) seems like it should work: import ctypes ODBC_ADD_DSN = 1 def add_dsn(name, driver, **kw): nul, attrib = chr(0), [] kw['DSN'] = name for attr, val in kw.iteritems(): attrib.append('%s=%s' % (attr, val)) return ctypes.windll.ODBCCP32.SQLConfigDataSource(0, ODBC_ADD_DSN, driver, nul.join(attrib)) == 1 print add_dsn('SAS Test', 'SAS', description = 'Testing SAS') But it pops up the SAS ODBC configuration dialog, sets the datasource name, and waits for the user to enter the information and dismiss the dialog. How can I avoid that?

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• I would like to learn C++, what is the first step ?

  - by Cesar

  My actual experience comes from PHP and Delphi(Borland) and recently also from Obj-C (iPhone sdk). In the past I also used Java, Python, VB 6 and some other scripting language. I would like to learn C++ because i need a standard tool for write compiled applications with good performance but i have no idea about witch environment i have to choose (Ex: Borland, Microsoft, Eclipse+MinGW, ...). Based those parameters: Most useful more opensource project or work requests Most standard not a proprietary versions Biggest community documentation, manuals, tutorials, forums... Better IDE add-ons, highlight, debug, cross platform, autocomplete... Easy setup A simple setup, to focus on learning the basics Actually I'm on OSX but I can use a VM if needed. Advices about tutorial or books are welcome. I hope it's not too generic as question.

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• Test-driven Development: Writing tests for private / protected variables

  - by Chetan

  I'm learning TDD, and I have a question about private / protected variables. My question is: If a function I want to test is operating on a private variable, how should I test it? Here is the example I'm working with: I have a class called Table that contains an instance variable called internalRepresentation that is a 2D array. I want to create a function called multiplyValuesByN that multiplies all the values in the 2D array by the argument n. So I write the test for it (in Python): def test_multiplyValuesByN (self): t = Table(3, 3) # 3x3 table, filled with 0's t.set(0, 0, 4) # Set value at position (0,0) to 4 t.multiplyValuesByN(3) assertEqual(t.internalRepresentation, [[12, 0, 0], [0, 0, 0], [0, 0, 0]]) Now, if I make internalRepresentation private or protected, this test will not work. How am I supposed to write the test so it doesn't depend on internalRepresentation but still tests that it looks correct after calling multiplyValuesByN?

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• How can I use Object Oriented Javascript to interact with HTML Objects

  - by Steve

  I am very new to object orientated javascript, with experience writing gui's in python and java. I am trying to create html tables that I can place in locations throughout a webpage. Each html table would have two css layouts that control if it is selected or not. I can write all of the interaction if I only have one table. It gets confusing when I have multiple tables. I am wondering how to place these tables throughout a blank webpage and then access the tables individually. I think I am having trouble understanding how inheritance and hierarchy works in javascript/html. NOTE: I am not asking how to make a table. I am trying to dynamically create multiple tables and place them throughout a webpage. Then access their css independently and change it (move them to different locations or change the way the look, independently of the other tables).

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• Anonymous iterator blocks in Clojure?

  - by Checkers

  I am using clojure.contrib.sql to fetch some records from an SQLite database. (defn read-all-foo [] (with-connection *db* (with-query-results res ["select * from foo"] (into [] res)))) Now, I don't really want to realize the whole sequence before returning from the function (i.e. I want to keep it lazy), but if I return res directly or wrap it some kind of lazy wrapper (for example I want to make a certain map transformation on result sequence), SQL-related bindings will be reset and connection will be closed after I return, so realizing the sequence will throw an exception. How can I enclose the whole function in a closure and return a kind of anonymous iterator block (like yield in C# or Python)? Or is there another way to return a lazy sequence from this function?

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• Which language + framework should I use for building standalone clients for my PHP webapp?

  - by Jagira

  Hello, I have a PHP web application which basically maintains a set of user profiles and their records. My users are using the app via browser. I am planning to build a standalone desktop client/app for WINDOWS OS, in which a user can login, retrieve and modify the records. Which language + framework will be simple, fast and lightweight to use? I can think of the following options: Microsoft Visual Basic - simplest? Microsoft Visual C++ Python PHP + bambalam compiler Are there any other options? And which of these is better?

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• How to hash and check for equality of objects with circular references

  - by mfya

  I have a cyclic graph-like structure that is represented by Node objects. A Node is either a scalar value (leaf) or a list of n=1 Nodes (inner node). Because of the possible circular references, I cannot simply use a recursive HashCode() function, that combines the HashCode() of all child nodes: It would end up in an infinite recursion. While the HashCode() part seems at least to be doable by flagging and ignoring already visited nodes, I'm having some troubles to think of a working and efficient algorithm for Equals(). To my surprise I did not find any useful information about this, but I'm sure many smart people have thought about good ways to solve these problems...right? Example (python): A = [ 1, 2, None ]; A[2] = A B = [ 1, 2, None ]; B[2] = B A is equal to B, because it represents exactly the same graph. BTW. This question is not targeted to any specific language, but implementing hashCode() and equals() for the described Node object in Java would be a good practical example.

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• Django: Data corrupted after loading? (possible programmer error)

  - by Rosarch

  I may be loading data the wrong way. excerpt of data.json: { "pk": "1", "model": "myapp.Course", "fields": { "name": "Introduction to Web Design", "requiredFor": [9], "offeringSchool": 1, "pre_reqs": [], "offeredIn": [1, 5, 9] } }, I run python manage.py loaddata -v2 data: Installed 36 object(s) from 1 fixture(s) Then, I go to check the above object using the Django shell: >>> info = Course.objects.filter(id=1) >>> info.get().pre_reqs.all() [<Course: Intermediate Web Programming>] # WRONG! There should be no pre-reqs >>> from django.core import serializers >>> serializers.serialize("json", info) '[{"pk": 1, "model": "Apollo.course", "fields": {"pre_reqs": [11], "offeredIn": [1, 5, 9], "offeringSchool": 1, "name": "Introduction to Web Design", "requiredFor": [9]}}]' The serialized output of the model is not the same as the input that was given to loaddata. The output has a non-empty pre_req list, whereas the input's pre_reqs field is empty. What am I doing wrong?

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• input URL, output contents of "view page source", i.e. after javascript / etc, library or command-li

  - by Ryan Berckmans

  I need a scalable, automated, method of dumping the contents of "view page source" (DOM) to a file. Programs such as wget or curl will non-interactively retrieve a set of URLs, but do not execute javascript or any of that 'fancy stuff'. My ideal solution looks like any of the following (fantasy solutions): cat urls.txt | google-chrome --quiet --no-gui \ --output-sources-directory=~/urls-source (fantasy command line, no idea if flags like these exist) or cat urls.txt | python -c "import some-library; \ ... use some-library to process urls.txt ; output sources to ~/urls-source" As a secondary concern, I also need: dump all included javascript source to file (a la firebug) dump pdf/image of page to file (print to file)

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• efficient video format/codec for sparse & binary blob tracking

  - by user391339

  I am working on a blob tracking project and have many high-definition videos that I would like to reduce in size for storage and downstream tracking/shape-analysis. I want to use a lossless method that takes advantage of the black and white nature of the video as well as the fact that not much is moving between individual frames. The videos are quite sparse, with 5 to 10 b&w blobs per frame occupying <30% of the space in total, with each blob moving <5-10% of the field of view between frames and not changing shape too much between 2-3 frames. I will work in Python, Matlab, or LabView for this project, and could use a batch utility if available. It may be worthwhile to export the files as compressed image stacks if a proper video format can't be found. What are the pros and cons of this? A video codec uses correlations between neighboring frames, so it should be more efficient, but not if the wrong one is chosen or if it is improperly configured.

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• Why are most really fast servers written in C instead of C++?

  - by orokusaki

  I'm trying to decide which to learn and I've read all the "Which is better" questions/arguments, so I thought I'd get your take on something more specific. Is there a platform dependency issue that C++ developers run into with such applications? Or, is it because there are more C developers out there than C++? I also noticed that many more third party C modules exist for Python even thought C++ modules are supported. From what I've read on different threads the consensus is that C++ is easier and faster to write, and runs just as fast. Am I missing something really big. Examples: NGINX APE (comet server) Apache

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• Undefined / Uninitialized default values in a class

  - by Jir

  Let's suppose you have this class: class A { public: A () {} A (double val) : m_val(val) {} ~A () {} private: double m_val; }; Once I create an instance of A, how can I check if m_val has been initialized/defined? Put it in other words, is there a way to know if m_val has been initialized/defined or not? Something along the lines of the defined operator in Python, I suppose. (But correct me if I'm wrong.) I thought of modifying the class and the c-tors the following way: class A { public: A () : defined(false) {} A (double val) : m_val(val), defined(true) {} ~A () {} private: double m_val; bool defined; }; How do you rate this solution? Any suggestion? TIA, Chris

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• Is there a way to set up a Linux pipe to non-buffering or line-buffering?

  - by ern0

  My program is controlling an external application on Linux, passing in input commands via a pipe to the external applications stdin, and reading output result via a pipe from the external applications stdout. The problem is that writes to pipes are buffered by block, and not by line, and therefore delays occur before my app receives data output by the external application. The external application cannot be altered to add explicit fflush() calls. When I set the external application to /bin/cat -n (it echoes back the input, with line numbers added), it works correctly, it seems, cat flushes after each line. The only way to force the external application to flush, is sending exit command to it; as it receives the command, it flushes, and all the answers appears on the stdout, just before exiting. I'm pretty sure, that Unix pipes are appropiate solution for that kind of interprocess communication (pseudo server-client), but maybe I'm wrong. (I've just copied some text from a similar question: Force another program's standard output to be unbuffered using Python)

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• Keeping track of dirty blocks on a block device

  - by mikeY

  I'm looking for a way to keep track of what blocks on a block device are modified after a point in time. How I eventually want to use this for is to keep two 2TB disks in sync, one which only comes online (connected through USB) once a month. Without knowing what blocks have been modified, I have to go through the whole 2TB every time. I'm using a recent GNU/Linux OS and have C and Python experience. I'm hoping to avoid writing kernel level code as I don't have any experience in that area whatsoever. My current theory is that there should be some hooks somewhere where my code can get called when a disk flush is performed. Any ideas?

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• BeautifulSoup Parser Confusion - HTML

  - by lyngbym

  I'm trying to scrape some content off another site and I'm not sure why BeautifulSoup is producing this output. It is only finding a blank space inside the match, but the real HTML contains a large amount of markup. I apologize if this is something stupid on my part. I'm new to python. Here's my code: import sys import os import mechanize import re from BeautifulSoup import BeautifulSoup def scrape_trails(BASE_URL, data): #Get the trail names soup = BeautifulSoup(data) sitesDiv = soup.findAll("div", attrs={"id" : "sitesDiv"}) print sitesDiv def main(): BASE_URL = "http://www.dnr.state.mn.us/skiing/skipass/list.html" br = mechanize.Browser() data = br.open(BASE_URL).get_data() links = scrape_trails(BASE_URL, data) if __name__ == '__main__': main() If you follow that URL you can see the sitesDiv contains a lot of markup. I'm not sure if I'm doing something wrong or if this is just malformed markup that the script can't handle. Thanks!

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• Are there any embedded languages that can be embedded into C# and actionscript?

  - by AnthonyF

  I'm looking for a embedded language that can be used to script common code between a server app written in C# and a client app written in Flash/Actionscript. It is important that the embedded language interpreter run natively in the environment it is embedded into. For example, it cannot load any external C libraries (i.e. python, neko). Does such a thing exist for these two languages? Perhaps there is some minimal interpreter that could be easily ported to both? Thanks!

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• Why do so many mathematicians format code so poorly? [closed]

  - by marcog

  I have done a fair amount of programming together with mathematicians. Now I am even teaching some high school kids coming from a mathematics background how to program. Most of these people format their code so hideously it's hard to believe. I've even worked with and taught mathematicians who will fight the auto-indenter! Why is this so common amongst mathematicians? BTW, this is one reason I have started teaching Python. Yet still they find ways other than indentation to produce whacked coding styles!

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• Character encoding issues in MySQL

  - by Eric

  In my database we have fields where the data is not readable. I now know why it happened but I don't know how to fix it. I found a way to get the info back from the database: SELECT id, name FROM projects WHERE LENGTH(name) != CHAR_LENGTH(name); One of the rows returned shows: id | name ------------------------- 1008 | Cajón el Diablo This should be: id | name ------------------------- 1008 | Cajón el Diablo Can somebody help me figure out how to fix this problem? How can I convert this using SQL? Is SQL not good? If not, how about Python?

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