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• Change text_factory in Django/sqlite

  - by Krumelur

  I have a django project that uses a sqlite database that can be written to by an external tool. The text is supposed to be UTF-8, but in some cases there will be errors in the encoding. The text is from an external source, so I cannot control the encoding. Yes, I know that I could write a "wrapping layer" between the external source and the database, but I prefer not having to do this, especially since the database already contains a lot of "bad" data. The solution in sqlite is to change the text_factory to something like: lambda x: unicode(x, "utf-8", "ignore") However, I don't know how to tell the Django model driver this.

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• Is there a way to access the locale used by gettext under windows ?

  - by phtrivier

  I have a program where i18n is handled by gettext. The program works fine, however for some reason I need to know the name of the locale used by gettext at runtime (something like 'fr_FR') under win32. I looked into gettext sources, and there is a quite frightening function that computes it on all platforms (gl_locale_name, in a C file called "localename.h/c"). However, this file does not seem to be installed alongside gettext or libintl, so I can't seem to call the function. Is there another function provided by gettext to get this value ? Or in another package (boost, glib, anything ?) (On a related note, there is a thing called std::locale in the C++ standard library, and according to the doc calling std::locale("") should create a locale with the settings of the system, unless I am mistaken ... but then the name is 'C' under windows. Is it a viable way of getting the locale name ? What I am doing wrong ?)

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• Find all paths from root to leaves of tree in Scheme

  - by grifaton

  Given a tree, I want to find the paths from the root to each leaf. So, for this tree: D / B / \ A E \ C-F-G has the following paths from root (A) to leaves (D, E, G): (A B D), (A B E), (A C F G) If I represent the tree above as (A (B D E) (C (F G))) then the function g does the trick: (define (g tree) (cond ((empty? tree) '()) ((pair? tree) (map (lambda (path) (if (pair? path) (cons (car tree) path) (cons (car tree) (list path)))) (map2 g (cdr tree)))) (else (list tree)))) (define (map2 fn lst) (if (empty? lst) '() (append (fn (car lst)) (map2 fn (cdr lst))))) But this looks all wrong. I've not had to do this kind of thinking for a while, but I feel there should be a neater way of doing it. Any ideas for a better solution (in any language) would be appreciated.

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• Rails / JBuilder - Entity array with has_many attributes

  - by seufagner

  I have two models, Person and Image and I want return an json array of Persons with your Images. But I dont want return all Image attributes, but produces a different result. Code below: class Person < ActiveRecord::Base has_many :images, as: :imageable validates :name, presence: true accepts_nested_attributes_for :images, :reject_if => lambda { |img| img['asset'].blank? } end class Image < ActiveRecord::Base belongs_to :imageable, polymorphic: true mount_uploader :asset, ImageUploader validates :asset, presence: true end zzz.jbuilder.json template json.persons(@rodas, :id, :name, :images) json produced: { "rodas": [{ "id": 4, "name": "John", "images": [ { "asset": { "url": "/uploads/image/xxxx.png" } }, { "asset": { "url": "/uploads/image/yyyyy.jpeg" } } ]}, { "id": 19, "name": "Mary", "images": [ { "asset": { "url": "/uploads/image/kkkkkkk.png" } } ] }] } I want something like: { "rodas": [ { "id": 4, "name": "John", "images": [ "/uploads/image/xxxx.png" , "/uploads/image/yyyy.jpeg" ] }, { "id": 10, "name": "Mary", "images": [ "/uploads/image/dddd.png" , "/uploads/image/xxxx.jpeg" ] } ]}

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• How to always return a set number of records when using find_related_tags with acts-as-taggable-on

  - by hadees

  I'm using the acts-as-taggable-on gem and I need to use find_related_tags on my survey model to get back 3 surveys every time. In the event there aren't always 3 related I need to pick how ever many are related plus some random ones to get to 3. Additionally I have a method I wrote called completed_survey_ids which return an array of survey_ids that shouldn't be used because the user has already completed them. Also there is a rare case that there won't be enough surveys because the user has completed them all so in that event it is okay to return less surveys then requested. I did write a named_scope to handle getting rid of the completed_survey_ids that I think works named_scope :not, lambda { |survey_ids| {:conditions => "id NOT IN (#{survey_ids.join(',')})" } }

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• What, if any, is wrong with this definition of letrec in Scheme?

  - by Lajla

  R5RS gives proposed macro definitions for library forms of syntax: http://schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-10.html#%_sec_7.3 Which also defines letrec, in a very complicated way, certainly not how I would define it, I would simply use: (define-syntax letrec2 (syntax-rules () ((letrec2 ((name val) ...) body bodies ...) ((lambda () (define name val) ... body bodies ...))))) As far as I understand the semantics of letrec, which I use very often as a named let. It works in this way, however as I've had my fair share of debates with philosophers who think they can just disprove special relativity or established phonological theories, I know that when you think you have a simple solution to a complex problem, it's probably WRONG. There has got to be some point where this macro does not satify the semantics of letrec else they'd probably have used it. In this definition, the definitions are local to the body of the letrec, they can refer to each other for mutual recursion, I'm not quite sure what (if any) is wrong.

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• awk / sed script to remove text

  - by radman

  Hi, I am currently needed of way to programmatically remove some text from Makefiles that I am dealing with. Now the problem is that (for whatever reason) the makefiles are being generated with link commands of -l<full_path_to_library>/<library_name> when they should be generated with -l<library_name>. So what I need is a script to find all occurrences of -l/ and then remove up to and including the next /. Example of what I'm dealing with -l/home/user/path/to/boost/lib/boost_filesystem I need it to be -lboost_filesystem As could be imagined this is a stop gap measure until I fix the real problem (on the generation side) but in the meantime it would be a great help to me if this could work and I am not too good with my awk and sed. Thanks for any help.

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• Store return value of function in reference C++

  - by Ruud v A

  Is it valid to store the return value of an object in a reference? class A { ... }; A myFunction() { A myObject; return A; } //myObject goes out of scope here void mySecondFunction() { A& mySecondObject = myFunction(); } Is it possible to do this in order to avoid copying myObject to mySecondObject? myObject is not needed anymore and should be exactly the same as mySecondObject so it would in theory be faster just to pass ownership of the object from one object to another. (This is also possible using boost shared pointer but that has the overhead of the shared pointer.) Thanks in advance.

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• Website content hosted with Google. Good or bad?

  - by user305052

  I recently decided to host my styles.css and various scripts on Google Docs and link them into my website. I also have all my images hosted through Picasa so that they too will load much faster and consistently across users. My site has most of its traffic from Japan, Africa, and South America, so I assume there will be a performance boost for my users since my server is hosted in Hong Kong. I (in Canada) have measured my load times to be half of what they used to be. Basically it's a free CDN for my personal stuff. I'm not too sure about all of this yet, so here's my question: what are the caveats of this setup?

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• How to binding to bit datatype in SQL to Booleans/CheckBoxes in ASP.NET MVC 2 with DataAnnotations

  - by nvtthang

  I've got problem with binding data type boolean to checkbox in MVC 2 data annotations Here's my code sample: label> Is Hot </label> <%=Html.CheckBoxFor(model => model.isHot, new {@class="input" })%> It always raise this error message below at (model=model.isHot). Cannot convert lambda expression to delegate type 'System.Func<Framework.Models.customer,bool>' because some of the return types in the block are not implicitly convertible to the delegate return type Cannot implicitly convert type 'bool?' to 'bool'. An explicit conversion exists (are you missing a cast?) Please suggest me how can I solve this problem? Thanks in advance.

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• Error using MVCContrib TestHelper

  - by Brian McCord

  While trying to implement the second answer to a previous question, I am receiving an error. I have implemented the methods just as the post shows, and the first three work properly. The fourth one (HomeController_Delete_Action_Handler_Should_Redirect_If_Model_Successfully_Delete) gives this error: Could not find a parameter named 'controller' in the result's Values collection. If I change the code to: actual .AssertActionRedirect() .ToAction("Index"); it works properly, but I don't like the "magic string" in there and prefer to use the lambda method that the other poster used. My controller method looks like this: [HttpPost] public ActionResult Delete(State model) { try { if( model == null ) { return View( model ); } _stateService.Delete( model ); return RedirectToAction("Index"); } catch { return View( model ); } } What am I doing wrong?

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• Can I configure AutoMapper to read from custom column names when mapping from IDataReader?

  - by rohancragg

  Psuedo code for mapping configuration (as below) is not possible since the lambda only lets us access Type IDataReader, wheras when actually mapping, AutoMapper will reach into each "cell" of each IDataRecord while IDataReader.Read() == true: var mappingConfig = Mapper.CreateMap<IDataReader, IEnumerable<MyDTO>>(); mappingConfig.ForMember( destination => destination.???, options => options.MapFrom(source => source.???)); Can anyone think of a way to do this using AutoMapper configuration at runtime or just some other dynamic approach that meets the requirement below. The requirement is to support any incoming IDataReader which may have column names that don't match the property names of MyDTO and there is no naming convention I can rely on. Instead we'll ask the user at runtime to cross-reference the expected column names with the actual column names found in the IDataReader via IDataReader.GetSchemaTable().

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• What type of websites does memcached speed up

  - by Saif Bechan

  I have read this article about 400% boost of your website. This is done by a combination of nginx and memcached. The how-to part of this website is quite good, but i mis the part where it says to what types of websites this applies. I know nginx is a http engine, I need no explanation for that. I thought memcached had something to do with caching database result. However i don't understand what this has to do with the http request, can someone please explain that to me. Another question I have is for what types of websites is this used. I have a website where the important part of the website consist of data that changes often. Often being minutes. Will this method still apply to me, or should I just stick with the basic boring setup of apache and nothing else.

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• C++ Thread Safe Integer

  - by Paul Ridgway

  Hello everyone, I have currently created a C++ class for a thread safe integer which simply stores an integer privately and has public get a set functions which use a boost::mutex to ensure that only one change at a time can be applied to the integer. Is this the most efficient way to do it, I have been informed that mutexes are quite resource intensive? The class is used a lot, very rapidly so it could well be a bottleneck... Googleing C++ Thread Safe Integer returns unclear views and oppinions on the thread safety of integer operations on different architectures. Some say that a 32bit int on a 32bit arch is safe, but 64 on 32 isn't due to 'alignment' Others say it is compiler/OS specific (which I don't doubt). I am using Ubuntu 9.10 on 32 bit machines, some have dual cores and so threads may be executed simultaneously on different cores in some cases and I am using GCC 4.4's g++ compiler. Thanks in advance...

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• Should I use C++0x Features Now?

  - by svu2g

  With the official release of VS 2010, is it safe for me to start using the partially-implemented C++0x feature set in my new code? The features that are of interest to me right now are both implemented by VC++ 2010 and recent versions of GCC. These are the only two that I have to support. In terms of the "safety" mentioned in the first sentence: can I start using these features (e.g., lambda functions) and still be guaranteed that my code will compile in 10 years on a compiler that properly conforms to C++0x when it is officially released? I guess I'm asking if there is any chance that VC++ 2010 or GCC will end up like VC++ 6; it was released before the language was officially standardized and consequently allowed grossly ill-formed code to compile. After all, Microsoft does say that "10 is the new 6". ;)

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• Database structure for storing Bank-like accounts and transactions

  - by user1241320

  We're in the process of adding a bank-like sub-system to our own shop. We already have customers, so each will be given a sort of account and transactions of some kind will be possible (adding to the account or subtracting from it). So we at least need the account entity, the transaction one and operations will then have to recalculate overall balances. How would you structure your database to handle this? Is there any standard bank system have to use that I could mock? By the way, we're on mysql but will also look at some nosql solution for performance boost.

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• Paperclip - Validate File Type but not Presence

  - by Lowgain

  I am using paperclip to handle my file uploads, and in one situation I don't want the file to be mandatory. I do however want to make sure it is a specific file type when it is present. I have this: class TestModel < ActiveRecord::Base #stuff has_attached_file :sound #etc... validates_attachment_content_type :sound, :content_type => ['audio/mp3', 'application/x-mp3'] end And when I have no sound file present, it tells me it is not one of the valid content types. I've tried adding '' to the :content_type array, which also doesn't work! I also attempted creating a lambda procedure for the :if property, but I can't get it to run without some kind of error. Anything missing here?

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• Optimizing Dijkstra for dense graph?

  - by Jason

  Is there another way to calculate the shortest path for a near complete graph other than Dijkstra? I have about 8,000 nodes and about 18 million edges. I've gone through the thread "a to b on map" and decided to use Dijkstra. I wrote my script in Perl using the Boost::Graph library. But the result isn't what I expected. It took about 10+ minutes to calculate one shortest path using the call $graph-dijkstra_shortest_path($start_node,$end_node); I understand there are a lot of edges and it may be the reason behind the slow running time. Am I dead in the water? Is there any other way to speed this up?

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• How return a std::string from C's "getcwd" function

  - by rubenvb

  Sorry to keep hammering on this, but I'm trying to learn :). Is this any good? And yes, I care about memory leaks. I can't find a decent way of preallocating the char*, because there simply seems to be no cross-platform way. const string getcwd() { char* a_cwd = getcwd(NULL,0); string s_cwd(a_cwd); free(a_cwd); return s_cwd; } UPDATE2: without Boost or Qt, the most common stuff can get long-winded (see accepted answer)

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• Conditional type definitions

  - by pythonic metaphor

  I'm sure that boost has some functions for doing this, but I don't know the relevant libraries well enough. I have a template class, which is pretty basic, except for one twist where I need to define a conditional type. Here is the psuedo code for what I want struct PlaceHolder {}; template <typename T> class C{ typedef (T == PlaceHolder ? void : T) usefulType; }; How do I write that type conditional?

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• Potential problems porting to different architectures

  - by Brendan Long

  I'm writing a Linux program that currently compiles and works fine on x86 and x86_64, and now I'm wondering if there's anything special I'll need to do to make it work on other architectures. What I've heard is that for cross platform code I should: Don't assume anything about the size of a pointer, int or size_t Don't make assumptions about byte order (I don't do any bit shifting -- I assume gcc will optimize my power of two multiplication/division for me) Don't use assembly blocks (obvious) Make sure your libraries work (I'm using SQLite, libcurl and Boost, which all seem pretty cross-platform) Is there anything else I need to worry about? I'm not currently targeting any other architectures, but I expect to support ARM at some point, and I figure I might as well make it work on any architecture if I can. Also, regarding my second point about byte order, do I need to do anything special with text input? I read files with getline(), so it seems like that should be done automatically as well.

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• Access to nested methods when DSL

  - by Vyacheslav Loginov

  class Warcraft def initialize &block instance_eval &block end def method_missing name, *args, &block instance_variable_set("@#{name}".to_sym, args[0]) self.class.send(:define_method, name, proc { instance_variable_get("@#{name}")}) end def game &block @game = Game.new &block end class Game def initialize &block instance_eval &block end def method_missing name, *args, &block instance_variable_set("@#{name}".to_sym, args[0]) self.class.send(:define_method, name, proc { instance_variable_get("@#{name}")}) end end end warcraft = Warcraft.new do name "Warcraft III" battle_net :iccup game do side :sentinels hero "Furion" rune_appear_every 2 end end puts warcraft.inspect # => #<Warcraft:0x00000000be3e80 @name="Warcraft III", @battle_net=:iccup, @game=#<Warcraft::Game:0x000000009c6c38 @side=:sentinels, @hero="Furion", @rune_appear_every=2>> How to access nested methods? puts warcraft.battle_net # => iccup puts warcraft.side #=> #<Proc:[email protected]:9 (lambda)> puts warcraft.game #=> dsl.rb:18:in `instance_eval': block not supplied (ArgumentError) puts warcraft.game.side #=> dsl.rb:18:in `instance_eval': block not supplied (ArgumentError)

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• How to save and load an array of complex numbers using numpy.savetxt?

  - by ptomato

  I want to use numpy.savetxt() to save an array of complex numbers to a text file. Problems: If you save the complex array with the default format string, the imaginary part is discarded. If you use fmt='%s', then numpy.loadtxt() can't load it unless you specify dtype=complex, converters={0: lambda s: complex(s)}. Even then, if there are NaN's in the array, loading still fails. It looks like someone has inquired about this multiple times on the Numpy mailing list and even filed a bug, but has not gotten a response. Before I put something together myself, is there a canonical way to do this?

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• How to sort a list by the 2nd tuple element in python and C#

  - by user350468

  I had a list of tuples where every tuple consists of two integers and I wanted to sort by the 2nd integer. After looking in the python help I got this: sorted(myList, key=lambda x: x[1]) which is great. My question is, is there an equally succinct way of doing this in C# (the language I have to work in)? I know the obvious answer involving creating classes and specifying an anonymous delegate for the whole compare step but perhaps there is a linq oriented way as well. Thanks in advance for any suggestions.

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• How might one implement FileTimeToSystemTime?

  - by Billy ONeal

  Hello :) I'm writing a simple wrapper around the Win32 FILETIME structure. boost::datetime has most of what I want, except I need whatever date type I end up using to interpolate with Windows APIs without issues. To that end, I've decided to write my own things for doing this -- most of the operations aren't all that complicated. I'm implementing the TimeSpan - like type at this point, but I'm unsure how I'd implement FileTimeToSystemTime. I could just use the system's built-in FileTimeToSystemTime function, except FileTimeToSystemTime cannot handle negative dates -- I need to be able to represent something like "-12 seconds". How should something like this be implemented? Billy3

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