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  • How do I do automatic data serialization of data objects in Haskell

    - by Adam Gent
    One of the huge benefits in languages that have some sort of reflection/introspecition is that objects can be automatically constructed from a variety of sources. For example in Java I can use the same objects for persisting to a db (with Hibernate) serializing to XML (with JAXB) or serializing to JSON (json-lib). You can do the same in Ruby and Python also usually following some simple rules for properties or annotations for Java. Thus I don't need lots "Domain Transfer Objects". I can concentrate on the domain I am working in. It seems in very strict FP like Haskell and Ocaml this is not possible. Particularly Haskell. The only thing I have seen is doing some sort of preprocessing or meta-programming (ocaml). Is it just accepted that you have to do all the transformations from the bottom upwards? In other words you have to do lot of boring work to turn a data type in haskell into JSON/XML/DB Row object and back again into a data object.

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  • Innodb Queries Slow

    - by user105196
    I have redHat 5.3 (Tikanga) with Mysql 5.0.86 configued with RIAD 10 HW, I run an application inquiries from Mysql/InnoDB and MyIsam tables, the queries are super fast,but some quires on Innodb tables sometime slow down and took more than 1-3 seconds to run and these queries are simple and optimized, this problem occurred just on innodb tables in different time with random queries. Why is this happening only to Innodb tables? the below is the Innodb status and some Mysql variables: show innodb status\G ************* 1. row ************* Status: 120325 10:54:08 INNODB MONITOR OUTPUT Per second averages calculated from the last 19 seconds SEMAPHORES OS WAIT ARRAY INFO: reservation count 22943, signal count 22947 Mutex spin waits 0, rounds 561745, OS waits 7664 RW-shared spins 24427, OS waits 12201; RW-excl spins 1461, OS waits 1277 TRANSACTIONS Trx id counter 0 119069326 Purge done for trx's n:o < 0 119069326 undo n:o < 0 0 History list length 41 Total number of lock structs in row lock hash table 0 LIST OF TRANSACTIONS FOR EACH SESSION: ---TRANSACTION 0 0, not started, process no 29093, OS thread id 1166043456 MySQL thread id 703985, query id 5807220 localhost root show innodb status FILE I/O I/O thread 0 state: waiting for i/o request (insert buffer thread) I/O thread 1 state: waiting for i/o request (log thread) I/O thread 2 state: waiting for i/o request (read thread) I/O thread 3 state: waiting for i/o request (write thread) Pending normal aio reads: 0, aio writes: 0, ibuf aio reads: 0, log i/o's: 0, sync i/o's: 0 Pending flushes (fsync) log: 0; buffer pool: 0 132777 OS file reads, 689086 OS file writes, 252010 OS fsyncs 0.00 reads/s, 0 avg bytes/read, 0.00 writes/s, 0.00 fsyncs/s INSERT BUFFER AND ADAPTIVE HASH INDEX Ibuf: size 1, free list len 366, seg size 368, 62237 inserts, 62237 merged recs, 52881 merges Hash table size 8850487, used cells 3698960, node heap has 7061 buffer(s) 0.00 hash searches/s, 0.00 non-hash searches/s LOG Log sequence number 15 3415398745 Log flushed up to 15 3415398745 Last checkpoint at 15 3415398745 0 pending log writes, 0 pending chkp writes 218214 log i/o's done, 0.00 log i/o's/second BUFFER POOL AND MEMORY Total memory allocated 4798817080; in additional pool allocated 12342784 Buffer pool size 262144 Free buffers 101603 Database pages 153480 Modified db pages 0 Pending reads 0 Pending writes: LRU 0, flush list 0, single page 0 Pages read 151954, created 1526, written 494505 0.00 reads/s, 0.00 creates/s, 0.00 writes/s No buffer pool page gets since the last printout ROW OPERATIONS 0 queries inside InnoDB, 0 queries in queue 1 read views open inside InnoDB Main thread process no. 29093, id 1162049856, state: waiting for server activity Number of rows inserted 77675, updated 85439, deleted 0, read 14377072495 0.00 inserts/s, 0.00 updates/s, 0.00 deletes/s, 0.00 reads/s END OF INNODB MONITOR OUTPUT 1 row in set, 1 warning (0.02 sec) read_buffer_size = 128M sort_buffer_size = 256M tmp_table_size = 1024M innodb_additional_mem_pool_size = 20M innodb_log_file_size=10M innodb_lock_wait_timeout=100 innodb_buffer_pool_size=4G join_buffer_size = 128M key_buffer_size = 1G can any one help me ?

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  • Why can't I install psycopg2? (Python 2.6.4, PostgreSQL 8.4, OS X 10.6)

    - by cojadate
    After running python setup.py install I get the following: Warning: Unable to find 'pg_config' filebuilding 'psycopg2._psycopg' extension gcc-4.0 -arch ppc -arch i386 -fno-strict-aliasing -fno-common -dynamic -DNDEBUG -g -O3 - DPSYCOPG_DEFAULT_PYDATETIME=1 -DPSYCOPG_VERSION="2.2.1 (dt dec ext pq3)" -DPSYCOPG_EXTENSIONS=1 -DPSYCOPG_NEW_BOOLEAN=1 -DHAVE_PQFREEMEM=1 -DHAVE_PQPROTOCOL3=1 -I/Library/Frameworks/Python.framework/Versions/2.6/include/python2.6 -I. -c psycopg/psycopgmodule.c -o build/temp.macosx-10.3-fat-2.6/psycopg/psycopgmodule.o unable to execute gcc-4.0: No such file or directory error: command 'gcc-4.0' failed with exit status 1 There's probably something screamingly obvious there to anyone who knows the first thing about back-end web programming, but unfortunately it's all gobbledegook to me. The psycopg2 documentation was not helpful.

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  • iPad: CoreData FetchedRequest Ignores Changes in Predicate

    - by Michael
    Hi there, While programming an iPad-app, I'm just running into trouble using a fetchedResultsController with a "dynamic" predicate. it seems the changes to the predicate get ignored. No matter how the predicate changes, I always get the result of the first fetch ... same code runs without no problems on iphone-env (3.1.x) !! sample : - (void)performSearch:(NSString *)searchText { self.displaySearchResults = TRUE; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"searchWords contains[cd] %@", searchText]; [self.fetchedSearchResultsController.fetchRequest setPredicate:predicate]; NSError *error = nil; if (![self.fetchedSearchResultsController performFetch:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } if(deviceIsIPad) { [self showSearchResults]; } else { [cookBookOverview reloadData]; } } can anyone help plz ? btw.: excuse my painful english ;-)

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  • Help with Event-Based Components

    - by Joel in Gö
    I have started to look at Event-Based Components (EBCs), a programming method currently being explored by Ralf Wesphal in Germany, in particular. This is a really interesting and promising way to architect a software solution, and gets close to the age-old idea of being able to stick software components together like Lego :) A good starting point is the Channel 9 video here, and there is a fair bit of discussion in German at the Google Group on EBCs. I am however looking for more concrete examples - while the ideas look great, I am finding it hard to translate them into real code for anything more than a trivial project. Does anyone know of any good code examples (in C# preferably), or any more good sites where EBCs are discussed?

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  • How to use NSTableView's selectedRowIndexes?

    - by Jakub Lédl
    Hi guys, I'm just learning some basic programming in Objective C and Cocoa. I'm trying to get some data from NSTableView. Based on what I read in one tutorial, I wrote this: NSArray * items = [[itemsTableView selectedRowEnumerator] allObjects]; But then I learned that selectedRowEnumerator was deprecated already in 10.3 Panther and that I should use selectedRowIndexes. The problem is, I didn't find how to actually use the returned NSIndexSet to achieve the same result as with code written above. So, If anyone could give me a tip, I would be very grateful. Thanks.

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  • Media Archive System with branches?

    - by Ian McEwen
    In short, how can I get VCS features (revisioning, branching, and deduplication) for a media collection that's far too large for most/all VCS systems? Background I have a 300GB music folder; unfortunately, I only have the hard drive space for this on my desktop system. However, a good portion of my collection is FLAC; therefore, I could theoretically have a space-optimized version in which I transcode all the FLAC to mp3 or some other lossy format, and use only that version on the laptop. However, a portion of my collection isn't FLAC. And that which isn't FLAC shouldn't be transcoded to an equivalent format; it won't have any space savings, which is the point. Moreover, it shouldn't be duplicated: the mp3/ogg portions of the collection should probably be exactly the same files. Thoughts One solution is to have format-specific organization of my music folders, and use some script to transcode the FLAC directory to mp3 or such into another directory. Another is some sort of hack using entirely separate copies and symbolic links for deduplication, or something similar. But these also have a disadvantage of lacking versioning; I'd like to be able to reorganize my music collection, retag things, etc. and save history. This isn't key, but would be awfully nice. I can't see it as entirely unreasonable to set up VCS hooks or something equivalent to keep directory structure synced between two copies, update tags, and transcode FLAC automatically into the space-optimized copy. Basically, the system I really want is a version control system. Two branches: one archival/desktop branch including the FLAC, one space-optimized/laptop branch without it; most VCSes would deal well with whole chunks being the same files well by compressing in a reasonable way (i.e. don't keep two copies of the same data). I could also do a lot of what I talk about above with hooks. But I don't know of any VCS that would deal with a 300GB repository with almost 20k files. Many of them would just not even initialize the whole affair; others would just do it inexpressibly slowly or otherwise badly. checkpoint looks like it's designed for something close (it's at least for media), but wouldn't do deduplication well (and I'm not convinced I'd be able to script it to do things like automatic transcoding and directory-structure syncing). So. Is there anything out there that can do all this, or should I consider it a programming project?

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  • Function Object in Java .

    - by Tony
    I wanna implement a javascript like method in java , is this possible ? Say , I have a Person class : public class Person { private String name ; private int age ; // constructor ,accessors are omitted } And a list with Person objects: Person p1 = new Person("Jenny",20); Person p2 = new Person("Kate",22); List<Person> pList = Arrays.asList(new Person[] {p1,p2}); I wanna implement a method like this: modList(pList,new Operation (Person p) { incrementAge(Person p) { p.setAge(p.getAge() + 1)}; }); modList receives two params , one is a list , the other is the "Function object", it loops the list ,and apply this function to every element in the list. In functional programming language,this is easy , I don't know how java do this? Maybe could be done through dynamic proxy, does that have a performance trade off?

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  • iphone using 2 tableview

    - by Anonymous
    Hi, I 'm a iphone programming newbie. I m trying to implement an app with multi-level tableviews. The idea is if someone selects something on the first screen say then a new view opens(tableview) car make> list of models Honda > Acura, S2000,accord ... My challenge is to show the list of models in a new tableview & secondly change the size of hte list depending on the car selected. I have programmed so that when i select 'Honda' a new tableview opens. How do i populate data for the second table?? Any suggestions on how to proceed? thanks

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  • Using Python tuples as vectors

    - by Etaoin
    I need to represent immutable vectors in Python ("vectors" as in linear algebra, not as in programming). The tuple seems like an obvious choice. The trouble is when I need to implement things like addition and scalar multiplication. If a and b are vectors, and c is a number, the best I can think of is this: tuple(map(lambda x,y: x + y, a, b)) # add vectors 'a' and 'b' tuple(map(lambda x: x * c, a)) # multiply vector 'a' by scalar 'c' which seems inelegant; there should be a clearer, simpler way to get this done -- not to mention avoiding the call to tuple, since map returns a list. Is there a better option?

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  • how to create a particle system on iphone and retain the created particles?

    - by lukya
    Hi all, I need to create a particle system and retain the created particles. I need to shake / move the created particles with the iphone accelerometer. Also, the number of particles needs to be very high (I need to show sand!). I do not have any OpenGLES programming experience. After initial search, I found Cocos2D can be used for particle generation. But there is no way of retaining the particles in the CCParticle system. As a work around, I tried creating many sprites at the end of particle generation and shown them as particles. But moving few number of sprites with accelerometer drops the frame rate considerably. Please suggest how this can be achieved and whether I should look for some other framework or if some kind of similar demo code is available. Thanks, Swapnil

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  • What should be done first: Code reviews or Unit tests?

    - by goldenmean
    Hello, If a developer implements code for some module and wants to get it reviewed. What should be the order : *First unit test the module after designing test cases for the module, debugging and fixing the bugs and then give the modified code for peer code review (Pros- Code to be reviewed is 'clean' to a good extent. Reduces some avoidable review comments and rework. Cons- Developer might spend large time debugging/fixing a bug which could have pointed/anticipated in peer code reviews) Or *First do the code review with peers and then go for unit testing. What are your thoughts/experience on this? I believe this approach for unit testing, code reviewing should be programming language agnostic, but it would be interesting to know otherwise(if applicable) with specific examples. -AD

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  • Why the "mutable default argument fix" syntax is so ugly, asks python newbie

    - by Cawas
    Now following my series of "python newbie questions" and based on another question. Go to http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html#other-languages-have-variables and scroll down to "Default Parameter Values". There you can find the following: def bad_append(new_item, a_list=[]): a_list.append(new_item) return a_list def good_append(new_item, a_list=None): if a_list is None: a_list = [] a_list.append(new_item) return a_list So, question here is: why is the "good" syntax over a known issue ugly like that in a programming language that promotes "elegant syntax" and "easy-to-use"? Why not just something in the definition itself, that the "argument" name is attached to a "localized" mutable object like: def better_append(new_item, a_list=[].local): a_list.append(new_item) return a_list I'm sure there would be a better way to do this syntax, but I'm also almost positive there's a good reason to why it hasn't been done. So, anyone happens to know why?

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  • Importing ctype; embedding python in C++ application

    - by Drew
    I'm trying to embed python within a C++ based programming language (CCL: The compuatational control language, not that any of you have heard of it). Thus, I don't really have a "main" function to make calls from. I have made a test .cc program with a main, and when I compile it and run it, I am able to import my own python modules and system modules for use. When I embed my code in my CCL-based program and compile it (with g++), it seems I have most functionality, but I get the import error: ImportError: /usr/lib/python2.6/lib-dynload/_ctypes.so: undefined symbol: PyType_GenericNew Can someone explain this to me and how to go about solving it? It seems like I've linked the objects correctly. Thanks.

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  • How do I draw an ellipse with arbitrary orientation pixel by pixel?

    - by amc
    Hi, I have to draw an ellipse of arbitrary size and orientation pixel by pixel. It seems pretty easy to draw an ellipse whose major and minor axes align with the x and y axes, but rotating the ellipse by an arbitrary angle seems trickier. Initially I though it might work to draw the unrotated ellipse and apply a rotation matrix to each point, but it seems as though that could cause errors do to rounding, and I need rather high precision. Is my suspicion about this method correct? How could I accomplish this task more precisely? I'm programming in C++ (although that shouldn't really matter since this is a more algorithm-oriented question).

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  • Editting ForeignKey from "child" table

    - by profuel
    I'm programming on py with django. I have models: class Product(mymodels.Base): title = models.CharField() price = models.ForeignKey(Price) promoPrice = models.ForeignKey(Price, related_name="promo_price") class Price(mymodels.Base): value = models.DecimalField(max_digits=10, decimal_places=3) taxValue = models.DecimalField("Tax Value", max_digits=10, decimal_places=3) valueWithTax = models.DecimalField("Value with Tax", max_digits=10, decimal_places=3) I want to see INPUTs for both prices when editing product, but cannot find any possibility to do that. inlines = [...] works only from Price to Product, which is stupid in this case. Thanx for adnvance.

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  • 3 hash functions to best hash sliding window strings for a bloom filter with minimum collisions

    - by Duaa
    Hi all: I need 3 hash functions to hash strings of a sliding window moving over a text, to be used later to search within a bloom vector. I'm using C# in my programming I read something about rolling hash functions and cyclic polynomials, they are used for sliding window applications. But really, I did not find any codes, they are just descriptions So please, if anyone have any idea about 3 best C# hash functions to use with sliding window strings of fixed size (5-char), that consume less time and have minimum number of collisions, either they are rolling hash functions or others, please help me with some C# codes or links to hash functions names Duaa

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  • Give me a practical use-case of Multi-set

    - by Calm Storm
    I would like to know a few practical use-cases (if they are not related/tied to any programming language it will be better).I can associate Sets, Lists and Maps to practical use cases. For example if you wanted a glossary of a book where terms that you want are listed alphabetically and a location/page number is the value, you would use the collection TreeMap(OrderedMap which is a Map) Somehow, I can't associate MultiSets with any "practical" usecase. Does someone know of any uses? http://en.wikipedia.org/wiki/Multiset does not tell me enough :) PS: If you guys think this should be community-wiki'ed it is okay. The only reason I did not do it was "There is a clear objective way to answer this question".

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  • COM port - how to identify a device (.net/c#)

    - by argh
    Hi, I'm programming for Windows CE and I need to connect to a scanner. There is no problem - I know that it is on port COM0, but if I plug in another device earlier it gets another COM port... to get all com ports the easy way is: SerialPort.GetPortNames() But I don't know how to identify a device? Is there any standard way? I can't 'ping' it since there is one device that only sends data... it spams data all the time... and I don't know how to 'ping' a device...

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  • Ethics of assisting other programmers, where do we draw the line?

    - by Chris
    In general, not just in relation to stackoverflow, sometimes I'm asked a programming question for which the answer will probably be used for good purposes, but there is a chance that it could not be. Two recent examples which reminded me of some real world questions I've been asked are: Send email to many users, and keep a formless application from closing for a keyboard hook Though I don't believe the intent of the authors of those questions is in any way nefarious, occasionally someone does ask such a question for purposes of aiding a spamming effort, or creating a keylogger. Even though the questioner and answerers had good intent, a 3rd party could pervert those answers to create a piece of malware or a spam utility. Should we always trust the questioner to use the answer for good? Should we feel obligated to ask the purpose of a question, and how the answer will be used? And how can we prevent answers from being overheard (when asked verbally) or being referenced (when posted publicly online) and then used for unsavory purposes?

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  • What to know - for building a form with PHP and MySQL

    - by Tal Galili
    Hello all, I have three weeks to perform the following basic task. I wish to create an online form in PHP that will get 5 numbers and with them: save the numbers to a MySQL DB do a simple computation on the numbers and return them as an output to the visitor I already have a domain, hosting and a MySQL database+user. I don't know PHP, or SQL or databases. I do have prior knowledge in C and R (which means I have some of the basics of programming, and I am not intimidated of a new languages). My question are: Am I missing something? is there some other skill I should have for this task that I don't know of? What is a good way to learn the skills needed for the task I described? Hope the question isn't too basic/general. Thanks!

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  • Good way to cache data during Android application lifecycle?

    - by sniurkst
    Hello, keeping my question short, I have creating application with 3 activities, where A - list of categories, B - list of items, C - single item. Data displayed in B and C is parsed from online XML. But, if I go trough A - B1 - C, then back to A and then back to B1 I would like to have it's data cached somewhere so I wouldn't have to request XML again. I'm new to Android and Java programming, I've googled a lot and still can't find (or simply do not have an idea where to look) a way to do what I want. Would storing all received data in main activity A (HashMaps? ContentProviders?) and then passing to B and C (if they get same request that was before) be a good idea?

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  • Encryption using rijndael

    - by user363295
    Hi all. I'm quite new in programming .I wrote the below code in order to prompt the user for a password to encrypting a file, But it just work when the length of password is 8, What can I do on order to accepting any number of characters for the password? string pass = textBox2.Text.ToString(); string password = @"" + pass + ""; UnicodeEncoding UE = new UnicodeEncoding(); byte[] key = UE.GetBytes(password); FileStream fsCrypt = new FileStream(@"c:\\users\\new", FileMode.Create); name = fsCrypt.Name; RijndaelManaged RMCrypto = new RijndaelManaged(); CryptoStream cs = new CryptoStream(fsCrypt, RMCrypto.CreateEncryptor(key, key), CryptoStreamMode.Write); FileStream fsIn = new FileStream(filename, FileMode.Open); int data; while ((data = fsIn.ReadByte()) != -1) cs.WriteByte((byte)data);

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  • C# define string format of double/floats to be US english by default

    - by neil
    Hi, I have got several thousands of lines of a web application source code, initially written on a US development system, to maintain. It makes heavy use of SQL statement strings, which are combined on the fly, e.g. string SQL = "select * from table where double_value = " + Math.Round(double_value, 2); Don't comment on bad programming style, that doesn't help me in this case :) The cruix: My system uses a German locale, which in turn leads to wrong SQL statements, like this: "select * from table where double_value = 15,5" (Note the comma as decimal separator instead of a point). Question: What is the most "elegant" way to change the locale of the web app in this case) to US or UK in order to prevent being forced to change and inspect every single line of code? .net 3.5 is not an option (would give me the chance to overwrite ToString() in an extension class) Kind regards

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  • Must See Conference Videos for Python/Django Developers

    - by Koobz
    There's lots of good conference videos online regarding Python and Django development. Instead of watching ST:TNG at the computer, I figure it'd more productive to hone my knowledge . Fire away with some of your most inspiring and educational Python, Django, or simply programming related talks. Provide an explanation of why you found the talk useful. Examples: James Bennet on Re-usable Apps - Got me to take a serious look at django apps. Put together a fairly robust site in two days afterwards with django-cms, django-photologue, django-contact-form. Good advice on when your app is crossing boundaries and why it's good to err on the site of 'make it a separate app.'

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