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  • Extending Python and Objective-C

    - by chpwn
    I'm a fan of clean code. I like my languages to be able to express what I'm trying to do, but I like the syntax to mirror that too. For example, I work on a lot of programs in Objective-C for jailbroken iPhones, which patch other code using the method_setImplementation() function of the runtime. Or, in PyObjC, I have to use the syntax UIView.initWithFrame_(), which is also pretty awful and unreadable with the way the method names are structured. In both cases, the language does not support this in syntax. I've found three basic ways that this is done: Insane macros. Take a look at this "CaptainHook", it does what I'm looking for in a usable way, but it isn't quite clean and is a major hack. There's also "Logos", which implements a very nice syntax, but is written in Perl parsing my code with a ton of regular expressions. This scares me. I like the idea of adding a %hook ClassName, but not by using regular expressions to parse C or Objective-C. Finally, there is Cycript. This is an extension to JavaScript which interfaces with the Objective-C runtime and allows you to use Objective-C style code in your JavaScript, and inject that into other processes. This is likely the cleanest as it actually uses a parser for the JavaScript, but I'm not a huge fan of that language in general. Should, and how should, I create an extension to Python and Objective-C to allow me to do this? Is it worth writing a parser for my language to transform the syntax into something nicer, if it is only in a very specialized niche like this? Should I just live with the horrible syntax of the default Objective-C hooking or PyObjC?

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  • Mutability design patterns in Objective C and C++

    - by Mac
    Having recently done some development for iPhone, I've come to notice an interesting design pattern used a lot in the iPhone SDK, regarding object mutability. It seems the typical approach there is to define an immutable class NSFoo, and then derive from it a mutable descendant NSMutableFoo. Generally, the NSFoo class defines data members, getters and read-only operations, and the derived NSMutableFoo adds on setters and mutating operations. Being more familiar with C++, I couldn't help but notice that this seems to be a complete opposite to what I'd do when writing the same code in C++. While you certainly could take that approach, it seems to me that a more concise approach is to create a single Foo class, mark getters and read-only operations as const functions, and also implement the mutable operations and setters in the same class. You would then end up with a mutable class, but the types Foo const*, Foo const& etc all are effectively the immutable equivalent. I guess my question is, does my take on the situation make sense? I understand why Objective-C does things differently, but are there any advantages to the two-class approach in C++ that I've missed? Or am I missing the point entirely? Not an overly serious question - more for my own curiosity than anything else.

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  • Perl XML SAX parser emulating XML::Simple record for record

    - by DVK
    Short Q summary: I am looking a fast XML parser (most likely a wrapper around some standard SAX parser) which will produce per-record data structure 100% identical to those produced by XML::Simple. Details: We have a large code infrastructure which depends on processing records one-by-one and expects the record to be a data structure in a format produced by XML::Simple since it always used XML::Simple since early Jurassic era. An example simple XML is: <root> <rec><f1>v1</f1><f2>v2</f2></rec> <rec><f1>v1b</f1><f2>v2b</f2></rec> <rec><f1>v1c</f1><f2>v2c</f2></rec> </root> And example rough code is: sub process_record { my ($obj, $record_hash) = @_; # do_stuff } my $records = XML::Simple->XMLin(@args)->{root}; foreach my $record (@$records) { $obj->process_record($record) }; As everyone knows XML::Simple is, well, simple. And more importantly, it is very slow and a memory hog - due to being a DOM parser and needing to build/store 100% of data in memory. So, it's not the best tool for parsing an XML file consisting of large amount of small records record-by-record. However, re-writing the entire code (which consist of large amount of "process_record"-like methods) to work with standard SAX parser seems like an big task not worth the resources, even at the cost of living with XML::Simple. What I'm looking for is an existing module which will probably be based on a SAX parser (or anything fast with small memory footprint) which can be used to produce $record hashrefs one by one based on the XML pictured above that can be passed to $obj->process_record($record) and be 100% identical to what XML::Simple's hashrefs would have been. I don't care much what the interface of the new module is - e.g whether I need to call next_record() or give it a callback coderef accepting a record.

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  • Creating a shim Stream

    - by spender
    A decompression API that I am using has the following API: Decode(Stream inStream,Stream outStream) I'd like to create a wrapper around this API, such that I can create my own Stream class which offers up the decoded data. Stream decodedStream=new BlaDecodeStream(inStream); So that I can than use this stream as a parameter to the XmlReader constructor in the same way one might use the System.IO.Compression.GZipStream. As far as I can tell, the only other option is set outStream stream to a MemoryStream or to a FileStream and go in two hops. The files I am dealing with are enormous, so neither of these options are particularly attractive. Before I go reinventing the wheel, is there any prior art that I might be able to draw from, or something in the BCL I might have missed? The CircularStream implementation here would go some of the way to helping, but I'm really looking for something similar that would block (as opposed to over/underrun) when the Stream's internal buffer is 'empty' when reading from it and block when the internal buffer is full when writing to it. In this way it could serve as parameter outStream and simultaneously (i.e. from another thread) could be read from by the XmlReader.

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  • x86 instruction encoding tables

    - by Cheery
    I'm in middle of rewriting my assembler. While at it I'm curious about implementing disassembly as well. I want to make it simple and compact, and there's concepts I can exploit while doing so. It is possible to determine rest of the x86 instruction encoding from opcode (maybe prefix bytes are required too, a bit). I know many people have written tables for doing it. I'm not interested about mnemonics but instruction encoding, because it is an actual hard problem there. For each opcode number I need to know: does this instruction contain modrm? how many immediate fields does this instruction have? what encoding does an immediate use? is the immediate in field an instruction pointer -relative address? what kind of registers does the modrm use for operand and register fields? sandpile.org has somewhat quite much what I'd need, but it's in format that isn't easy to parse. Before I start writing and validating those tables myself, I decided to write this question. Do you know about this kind of tables existing somewhere? In a form that doesn't require too much effort to parse.

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  • C# File IO with Streams - Best Memory Buffer Size

    - by AJ
    Hi, I am writing a small IO library to assist with a larger (hobby) project. A part of this library performs various functions on a file, which is read / written via the FileStream object. On each StreamReader.Read(...) pass, I fire off an event which will be used in the main app to display progress information. The processing that goes on in the loop is vaired, but is not too time consuming (it could just be a simple file copy, for example, or may involve encryption...). My main question is: What is the best memory buffer size to use? Thinking about physical disk layouts, I could pick 2k, which would cover a CD sector size and is a nice multiple of a 512 byte hard disk sector. Higher up the abstraction tree, you could go for a larger buffer which could read an entire FAT cluster at a time. I realise with today's PC's, I could go for a more memory hungry option (a couple of MiB, for example), but then I increase the time between UI updates and the user perceives a less responsive app. As an aside, I'm eventually hoping to provide a similar interface to files hosted on FTP / HTTP servers (over a local network / fastish DSL). What would be the best memory buffer size for those (again, a "best-case" tradeoff between perceived responsiveness vs. performance). Thanks in advance for any ideas, Adam

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  • Java parsing XML document gives "Content not allowed in prolog." error

    - by thechiman
    I am writing a program in Java that takes a custom XML file and parses it. I'm using the XML file for storage. I am getting the following error in Eclipse. [Fatal Error] :1:1: Content is not allowed in prolog. org.xml.sax.SAXParseException: Content is not allowed in prolog. at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:239) at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:283 ) at javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:208) at me.ericso.psusoc.RequirementSatisfier.parseXML(RequirementSatisfier.java:61) at me.ericso.psusoc.RequirementSatisfier.getCourses(RequirementSatisfier.java:35) at me.ericso.psusoc.programs.RequirementSatisfierProgram.main(RequirementSatisfierProgram.java:23 ) The beginning of the XML file is included: <?xml version="1.0" ?> <PSU> <Major id="IST"> <name>Information Science and Technology</name> <degree>B.S.</degree> <option> Information Systems: Design and Development Option</option> <requirements> <firstlevel type="General_Education" credits="45"> <component type="Writing_Speaking">GWS</component> <component type="Quantification">GQ</component> The program is able to read in the XML file but when I call DocumentBuilder.parse(XMLFile) to get a parsed org.w3c.dom.Document, I get the error above. It doesn't seem to me that I have invalid content in the prolog of my XML file. I can't figure out what is wrong. Please help. Thanks.

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  • weak or strong for IBOutlet and other

    - by Piero
    I have switched my project to ARC, and I don't understand if I have to use strong or weak for IBOutlets. Xcode do this: in interface builder, if a create a UILabel for example and I connect it with assistant editor to my ViewController, it create this: @property (nonatomic, strong) UILabel *aLabel; It uses the strong, instead I read a tutorial on RayWenderlich website that say this: But for these two particular properties I have other plans. Instead of strong, we will declare them as weak. @property (nonatomic, weak) IBOutlet UITableView *tableView; @property (nonatomic, weak) IBOutlet UISearchBar *searchBar; Weak is the recommended relationship for all outlet properties. These view objects are already part of the view controller’s view hierarchy and don’t need to be retained elsewhere. The big advantage of declaring your outlets weak is that it saves you time writing the viewDidUnload method. Currently our viewDidUnload looks like this: - (void)viewDidUnload { [super viewDidUnload]; self.tableView = nil; self.searchBar = nil; soundEffect = nil; } You can now simplify it to the following: - (void)viewDidUnload { [super viewDidUnload]; soundEffect = nil; } So use weak, instead of the strong, and remove the set to nil in the videDidUnload, instead Xcode use the strong, and use the self... = nil in the viewDidUnload. My question is: when do I have to use strong, and when weak? I want also use for deployment target iOS 4, so when do I have to use the unsafe_unretain? Anyone can help to explain me well with a small tutorial, when use strong, weak and unsafe_unretain with ARC?

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  • Looping through python-dictionary-turned-into-json in javascript.

    - by Phil
    In writing a django app, I am returning the following json on a jQuery ajax call: { "is_owner": "T", "author": "me", "overall": "the surfing lifestyle", "score": "1", "meanings": { "0": "something", "1": "something else", "3": "yet something else", "23": "something random" }, "user vote": "1" } In the javascript/jQuery callback function, I can access the is_owner, author, etc. easily enough. is_owner = json.is_owner; author = json.author; But for meanings, the numbers are different depending on what it pulls from the server. On the server side for the meanings part, right now what I'm doing is constructing a dictionary like so: meanings_dict = {} meanings = requested_tayke.meanings.all() for meaning in meanings: meanings_dict[meaning.location] = meaning.text and then returning a json I create like this: test_json = simplejson.dumps({'is_owner':is_owner, 'overall':overall, 'score':str(score),'user vote':str(user_vote), 'author': author, 'meanings' : meanings_dict }) print test_json return HttpResponse(test_json) My question is this: how do I access the 'meanings' data from my json in javascript? I need to loop through all of it. Maybe I need to be loading it into json differently. I have full control so of both the server and client side so I'm willing to change either to make it work. Also worth noting: I'm not using Django's serialize functionality. I couldn't make it work with my situation.

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  • Creating A Single Generic Handler For Agatha?

    - by David
    I'm using the Agatha request/response library (and StructureMap, as utilized by Agatha 1.0.5.0) for a service layer that I'm prototyping, and one thing I've noticed is the large number of handlers that need to be created. It generally makes sense that any request/response type pair would need their own handler. However, as this scales to a large enterprise environment that's going to be A LOT of handlers. What I've started doing is dividing up the enterprise domain into logical processor classes (dozens of processors instead of many hundreds or possibly eventually thousands handlers). The convention is that each request/response type (all of which inherit from a domain base request/response pair, which inherit from Agatha's) gets exactly one function in a processor somewhere. The generic handler (which inherits from Agatha's RequestHandler) then uses reflection in the Handle method to find the method for the given TREQUEST/TRESPONSE and invoke it. If it can't find one or if it finds more than one, it returns a TRESPONSE containing an error message (messages are standardized in the domain's base response class). The goal here is to allow developers across the enterprise to just concern themselves with writing their request/response types and processor functions in the domain and not have to spend additional overhead creating handler classes which would all do exactly the same thing (pass control to a processor function). However, it seems that I still need to have defined a handler class (albeit empty, since the base handler takes care of everything) for each request/response type pair. Otherwise, the following exception is thrown when dispatching a request to the service: StructureMap Exception Code: 202 No Default Instance defined for PluginFamily Agatha.ServiceLayer.IRequestHandler`1[[TSFG.Domain.DTO.Actions.HelloWorldRequest, TSFG.Domain.DTO, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]], Agatha.ServiceLayer, Version=1.0.5.0, Culture=neutral, PublicKeyToken=6f21cf452a4ffa13 Is there a way that I'm not seeing to tell StructureMap and/or Agatha to always use the base handler class for all request/response type pairs? Or maybe to use Reflection.Emit to generate empty handlers in memory at application start just to satisfy the requirement? I'm not 100% familiar with these libraries and am learning as I go along, but so far my attempts at both those possible approaches have been unsuccessful. Can anybody offer some advice on solving this, or perhaps offer another approach entirely?

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  • Python + QT + Gstreamer

    - by Ptterb
    Hi everyone, I'm working with PyQt and trying to get video from a webcam to play within a QT widget. I've found tutorials for C and Qt, and for python and gtk, but NOTHING for this combo of pyQt and gstreamer. Anybody get this working? This plays the video fine, but in a separate window: self.gcam = gst.parse_launch('v4l2src device=/dev/video0 ! autovideosink') self.gcam.set_state(gst.STATE_PLAYING) what I need is to get the overlay working so it's displayed within a widget on my GUI. Thanks, Gurus of the internet! ok, so I've gotten a lot farther, but still in need of some help. I'm actually writing this for Maemo, but the following code works fine on my linux laptop: class Vid: def __init__(self, windowId): self.player = gst.Pipeline("player") self.source = gst.element_factory_make("v4l2src", "vsource") self.sink = gst.element_factory_make("autovideosink", "outsink") self.source.set_property("device", "/dev/video0") self.scaler = gst.element_factory_make("videoscale", "vscale") self.window_id = None self.windowId = windowId self.player.add(self.source, self.scaler, self.sink) gst.element_link_many(self.source,self.scaler, self.sink) bus = self.player.get_bus() bus.add_signal_watch() bus.enable_sync_message_emission() bus.connect("message", self.on_message) bus.connect("sync-message::element", self.on_sync_message) def on_message(self, bus, message): t = message.type if t == gst.MESSAGE_EOS: self.player.set_state(gst.STATE_NULL) elif t == gst.MESSAGE_ERROR: err, debug = message.parse_error() print "Error: %s" % err, debug self.player.set_state(gst.STATE_NULL) def on_sync_message(self, bus, message): if message.structure is None: return message_name = message.structure.get_name() if message_name == "prepare-xwindow-id": win_id = self.windowId assert win_id imagesink = message.src imagesink.set_property("force-aspect-ratio", True) imagesink.set_xwindow_id(win_id) def startPrev(self): self.player.set_state(gst.STATE_PLAYING) print "should be playing" vidStream = Vid(wId) vidStream.startPrev() where wId is the window id of the widget im trying to get to display the output in. When I run this on the N900, the screen goes black and blinks. Any ideas? I'm dying here!

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  • Modify Django Forms

    - by Ninefingers
    Hi All, I've recently been developing on the django platform and have stumbled upon Django Forms (forms.Form/forms.ModelForm) as ways of creating <form> html. Now, this is brilliant for quick stuff but what I'm trying to do is a little bit more complicated. Consider a DateField - my current form has fields for day, month and year and constructs a python date object from that. However, a django form creates a single textbox in which the correct format (say 2010-06-15) must be entered. As another example, for large fields I need to replace <input> with <textarea>. I'd like to take advantage of Django's forms for simple validation but I need something simpler for my users. So my question is: can I intercept the rendering of one of these objects to write out the html as I like? If so, do I have to do all the writing myself or can I only do those objects I wish to re-write? Thanks in advance.

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  • Linq to SQL DynamicInvoke(System.Object[])' has no supported translation to SQL.

    - by ewwwyn
    I have a class, Users. Users has a UserId property. I have a method that looks something like this: static IQueryable<User> FilterById(this IQueryable<User> p, Func<int, bool> sel) { return p.Where(m => sel(m)); } Inevitably, when I call the function: var users = Users.FilterById(m => m > 10); I get the following exception: Method 'System.Object DynamicInvoke(System.Object[])' has no supported translation to SQL. Is there any solution to this problem? How far down the rabbit hole of Expression.KillMeAndMyFamily() might I have to go? To clarify why I'm doing this: I'm using T4 templates to autogenerate a simple repository and a system of pipes. Within the pipes, instead of writing: new UserPipe().Where(m => m.UserId > 10 && m.UserName.Contains("oo") && m.LastName == "Wee"); I'd like to generate something like: new UserPipe() .UserId(m => m > 10) .UserName(m => m.Contains("oo")) .LastName("Wee");

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  • Graphviz or Dynagraph for Graph-manipulation Program?

    - by noahlavine
    I'm looking into writing a program that will show a graph to the user. The graph will change over time (the user should be able to right-click on a graph item and ask for more detail, which will pop out new bits of the graph), and the user might be able to drag parts of the graph around. I would ideally also like to be able to specify the relative layout of certain parts of the graph myself while leaving the overall layout up to a library, but that's not essential. I'm trying to decide on a graph layout library to use. As far as I can tell, the two leading candidates are Graphviz and Dynagraph. The Dynagraph website suggests that Graphviz is for drawing static graphs, and that Dynagraph was forked from Graphviz and contains algorithms for graphs that will be updated. It has a sample program called Dynasty that does exactly what I want. However, the Graphviz site contains an example program called Lefty which seems to do exactly what I want. Graphviz also seems to be much more widely used, judging by Google (and SO) results. Finally, I'd like to code the GUI part in a language like Python or Scheme, which makes me a bit hesitant to use C++ because I understand it's harder to interface that to interpreters. So my question is, which library is better for what I'm trying to do? Do they both have strong and weak points? Has one of them actually ceased development and is just leaving its website up to confuse me? (I've seen http://stackoverflow.com/questions/464000/simple-dynamic-graph-display-for-c and http://stackoverflow.com/questions/2376987/open-source-libraries-to-design-directed-graphs, but I can't tell whether they're right about the Graphviz or Dynagraph choice because of Lefty and also the language issue.)

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  • Why does Tfs2010 build my Wix project before anything else?

    - by bwerks
    Hi all, A similar question was asked and answered about a year ago, but was either a different issue (everything was in beta) or misdiagnosed. It's located here: http://stackoverflow.com/questions/688162/msbuild-task-fails-because-any-cpu-solution-is-built-out-of-order. My issue is that I have a wix installer project, and after upgrading to Tfs2010 on monday, the build fails on linking because it can't find the build product of the Wpf application in the project. After some digging, it's because it hasn't been built yet. Building in Vs2010 works as normal. The wix project is set to depend on the Wpf project, and when viewing Project Build Order in the IDE, everything looks as normal. The problem was originally encountered with only two platform definitions in the solution; x86 and x64. There are also two flavors, Debug and Release, and TFSBuild.proj is set to build all four combinations. There was no occurence of AnyCPU anywhere. Per the referenced question above, I tried changing the Wpf project to use AnyCPU so that it would be built first. At this point, the wix project used the exact configuration and the Wpf project used the flavor with AnyCPU. However, doing so didn't seem to change anything. I'm using the Tfs2010 RTM, Vs2010 RTM, and the most recent version of Wix, which at the time of this writing is 3.5.1602.0, from 2010-04-02. Anyone else running into this?

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  • Call private methods and private properties from outside a class in PHP

    - by Pablo López Torres
    I want to access private methods and variables from outside the classes in very rare specific cases. I've seen that this is not be possible although introspection is used. The specific case is the next one: I would like to have something like this: class Console { final public static function run() { while (TRUE != FALSE) { echo "\n> "; $command = trim(fgets(STDIN)); switch ($command) { case 'exit': case 'q': case 'quit': echo "OK+\n"; return; default: ob_start(); eval($command); $out = ob_get_contents(); ob_end_clean(); print("Command: $command"); print("Output:\n$out"); break; } } } } This method should be able to be injected in the code like this: Class Demo { private $a; final public function myMethod() { // some code Console::run(); // some other code } final public function myPublicMethod() { return "I can run through eval()"; } private function myPrivateMethod() { return "I cannot run through eval()"; } } (this is just one simplification. the real one goes through a socket, and implement a bunch of more things...) So... If you instantiate the class Demo and you call $demo-myMethod(), you'll get a console: that console can access the first method writing a command like: > $this->myPublicMethod(); But you cannot run successfully the second one: > $this->myPrivateMethod(); Do any of you have any idea, or if there is any library for PHP that allows you to do this? Thanks a lot!

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  • How do I dynamically create a document for download in Javascript?

    - by Nelson
    I'm writing some Javascript code that generates an XML document in the client (via Google Earth plugin). I'd like the user to be able to click a button on the page and be prompted to save that XML to a new file. If I were generating the XML server-side this would be easy, just make the button open the link. But the XML is generated client-side. I've come up with a couple of hacks that half-work, inspired in part by this StackOverflow question. But neither completely work. Here's a demo HTML with embedded code: <html><head><script> function getData() { return '<?xml version="1.0" encoding="UTF-8"?><doc>Hello</doc>'; } function dlDataURI() { window.open("data:text/xml;charset=utf-8," + getData()); } function dlWindow() { var w = window.open(); w.document.open(); w.document.write(getData()); w.document.close(); } </script><body> <div onclick="dlDataURI()">Click for Data URL</div> <div onclick="dlWindow()">Click for Window</div> </body></html> The dlDataURI() version works great in Firefox, poorly in Chrome (can't save), and not at all in IE. The Window() version works OK in Firefox and IE, and not well in Chrome (can't save, XML embedded inside HTML). Neither version ever prompts a user download, it always opens a new window trying to display the XML. Is there a good way to do what I want in client side Javascript? I'd like this to work in today's browsers, ideally Firefox, MSIE 8, and Chrome.

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  • Factories, or Dependency Injection for object instantiation in WCF, when coding against an interface

    - by Saajid Ismail
    Hi I am writing a client/server application, where the client is a Windows Forms app, and the server is a WCF service hosted in a Windows Service. Note that I control both sides of the application. I am trying to implement the practice of coding against an interface: i.e. I have a Shared assembly which is referenced by the client application. This project contains my WCF ServiceContracts and interfaces which will be exposed to clients. I am trying to only expose interfaces to the clients, so that they are only dependant on a contract, not any specific implementation. One of the reasons for doing this is so that I can have my service implementation, and domain change at any time without having to recompile and redeploy the clients. The interfaces/contracts will in this case not change. I only need to recompile and redeploy my WCF service. The design issue I am facing now, is: on the client, how do I create new instances of objects, e.g. ICustomer, if the client doesn't know about the Customer concrete implementation? I need to create a new customer to be saved to the DB. Do I use dependency injection, or a Factory class to instantiate new objects, or should I just allow the client to create new instances of concrete implementations? I am not doing TDD, and I will typically only have one implementation of ICustomer or any other exposed interface.

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  • How to test IO code in JUnit?

    - by add
    I'm want to test two services: service which builds file name service which writes some data into file provided by 1st service In first i'm building some complex file structure (just for example {user}/{date}/{time}/{generatedId}.bin) In second i'm writing data to the file passed by first service (1st service calls 2nd service) How can I test both services using mocks without making any real IO interractions? Just for example: 1st service: public class DefaultLogService implements LogService { public void log(SomeComplexData data) { serializer.write(new FileOutputStream(buildComplexFileStructure()), data); or serializer.write(buildComplexFileStructure(), data); or serializer.write(new GenericInputEntity(buildComplexFileStructure()), data); } private ComplextDataSerializer serializer; // mocked in tests } 2nd service: public class DefaultComplexDataSerializer implements ComplexDataSerializer { void write(InputStream stream, SomeComplexData data) {...} or void write(File file, SomeCompexData data) {...} or void write(GenericInputEntity entity, SomeComplexData data) {...} } In first case i need to pass FileOutputStream which will create a file (i.e. i can't test 1st service) In second case i need to pass File. What can i do in 2nd service test if I need to test data which will be written to specified file? (i can't test 2nd service) In third case i think i need some generic IO object which will wrap File. Maybe there is some ready-to-use solution for this purpose?

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  • Manditory read-only fields in django

    - by jamida
    I'm writing a test "grade book" application. The models.py file is shown below. class Student(models.Model): name = models.CharField(max_length=50) parent = models.CharField(max_length=50) def __unicode__(self): return self.name class Grade(models.Model): studentId = models.ForeignKey(Student) finalGrade = models.CharField(max_length=3) I'd like to be able to change the final grade for several students in a modelformset but for now I'm just trying one student at a time. I'm also trying to create a form for it that shows the student name as a field that can not be changed, the only thing that can be changed here is the finalGrade. So I used this trick to make the studentId read-only. class GradeROForm(ModelForm): studentId = forms.ModelChoiceField(queryset=Student.objects.all()) def __init__(self, *args, **kwargs): super(GradeROForm,self).__init__(*args, **kwargs) instance = getattr(self, 'instance', None) if instance and instance.id: self.fields['studentId'].widget.attrs['disabled']='disabled' def clean_studentId(self): instance = getattr(self,'instance',None) if instance: return instance.studentId else: return self.cleaned_data.get('studentId',None) class Meta: model=Grade And here is my view: def modifyGrade(request,student): student = Student.objects.get(name=student) mygrade = Grade.objects.get(studentId=student) if request.method == "POST": myform = GradeROForm(data=request.POST, instance=mygrade) if myform.is_valid(): grade = myform.save() info = "successfully updated %s" % grade.studentId else: myform=GradeROForm(instance=mygrade) return render_to_response('grades/modifyGrade.html',locals()) This displays the form like I expect, but when I hit "submit" I get a form validation error for the student field telling me this field is required. I'm guessing that, since the field is "disabled", the value is not being reported in the POST and for reasons unknown to me the instance isn't being used in its place. I'm a new Django/Python programmer, but quite experienced in other languages. I can't believe I've stumbled upon such a difficult to solve problem in my first significant django app. I figure I must be missing something. Any ideas?

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  • How to group strings by prefix

    - by namenlos
    I am writing a Winform UI in which the user must select a single customer. (For reasons beyond my control I am limited to a UI that uses dropdown lists, text fields, checkboxes, radiobuttons only -i.e. no fancy special UI controls) The situation There are a lot of customers (a thousand for example) If i put all the customers in a single dropdown there's no way it will be easy for a customer to even see all the customers. Also the it will take too long to retireve all the customers from the DB to populate the dropdown My thought is to have two combo box, the first lists groups of the customers by their last name something like a phone book "Aa-Ac", "Ad-Ade", "Adf-B", when selecting the first combo box, it scope the second one to a managable set customer names (no more than for example 40 names) The question I need a reasonable way of grouping their names such that it will be clear to customer which group contains the name. I.e. given a group of names I need to bucketize then int "Aa-Ac". Comments I don't need to solve the general problem of an immense number of names - we know based on our data that 1000 names is the max our users will encounter. If there are other techniques please do share, but I am interested specifically in an answer to my specific question around how to determine the buckets ("Aa-Ac", etc.)

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  • Get coordinates of google maps markers

    - by App_beginner
    I am creating a databse containing the names and coordinates of all bus stops in my local area. I have all the names stored in my database, and now I need to add the coordinates. I am trying to get these of a website that contains them all as placemarks on a google map. It seems to me like they are being generated from a local server, and then added to the map. However I am unable to find exactly where the server is queried for the coordinates. I am hoping to collect these coordinates through the use of a screen scraper. However unless I am able to find where in the source code the coordinates are created this seems to be impossible. I can of course search and collect all these placemarks manually, but that will be very time consuming. So I am hoping that someone in here can help me. This is the website I am trying to scrape. The placemarks are marked by the blue bus sign: http://reiseplanlegger.skyss.no/scripts/travelmagic/TravelMagicWE.dll/?from=Brimnes+ferjekai+%28Eidfjord%29&to= You can also get the coordinates of a single placemark by writing the name of the stop in the search field and pushing the "Vis i kart" button. I hope someone can help me with this.

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  • What is the most platform- and Python-version-independent way to make a fast loop for use in Python?

    - by Statto
    I'm writing a scientific application in Python with a very processor-intensive loop at its core. I would like to optimise this as far as possible, at minimum inconvenience to end users, who will probably use it as an uncompiled collection of Python scripts, and will be using Windows, Mac, and (mainly Ubuntu) Linux. It is currently written in Python with a dash of NumPy, and I've included the code below. Is there a solution which would be reasonably fast which would not require compilation? This would seem to be the easiest way to maintain platform-independence. If using something like Pyrex, which does require compilation, is there an easy way to bundle many modules and have Python choose between them depending on detected OS and Python version? Is there an easy way to build the collection of modules without needing access to every system with every version of Python? Does one method lend itself particularly to multi-processor optimisation? (If you're interested, the loop is to calculate the magnetic field at a given point inside a crystal by adding together the contributions of a large number of nearby magnetic ions, treated as tiny bar magnets. Basically, a massive sum of these.) # calculate_dipole # ------------------------- # calculate_dipole works out the dipole field at a given point within the crystal unit cell # --- # INPUT # mu = position at which to calculate the dipole field # r_i = array of atomic positions # mom_i = corresponding array of magnetic moments # --- # OUTPUT # B = the B-field at this point def calculate_dipole(mu, r_i, mom_i): relative = mu - r_i r_unit = unit_vectors(relative) #4pi / mu0 (at the front of the dipole eqn) A = 1e-7 #initalise dipole field B = zeros(3,float) for i in range(len(relative)): #work out the dipole field and add it to the estimate so far B += A*(3*dot(mom_i[i],r_unit[i])*r_unit[i] - mom_i[i]) / sqrt(dot(relative[i],relative[i]))**3 return B

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  • Would OpenID or OAuth work for authorization/authentication on a distributed web service?

    - by David Eyk
    We're in the early stages of designing a RESTful/resource-oriented web service API for a computational lingustics application. Because many of the resources we plan to serve are rights-encumbered, a key design decision has been to specify the platform so that each resource provider can expose their own web service that complies with the API spec. This way, the rights owner maintains control over their content (and thus the ability to throttle or deny access at will) and a direct relationship with the consumer, while still being able to participate in in the collaborative network. At the same time, to simplify the job of writing a client for this service, we want to allow a client access to the distributed service through one end-point, with the server handling content negotiation and retrieval from the appropriate providers. Right now, we're at an impasse on authentication/authorization schemes. One of our number has argued for the (technical) simplicity of a central authentication registry, but others are concerned about the organizational complexity of such a scheme. It seems to me, based on an albeit limited understanding of the technologies, that a combination of OpenID and OAuth would do the trick, with a client authenticating with the end-point via OpenID, and the server taking action on the user's behalf with the various content providers using OAuth. I've only ever seen implementations (e.g. stackoverflow, twitter, etc.) where a human was present to intervene, and I still need to do more research on these technologies. Would a scheme like this work for an automated web service, or would it make the client too difficult to implement and operate?

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  • How to have Android Service communicate with Activity

    - by Scott Saunders
    I'm writing my first Android application and trying to get my head around communication between services and activities. I have a Service that will run in the background and do some gps and time based logging. I will have an Activity that will be used to start and stop the Service. So first, I need to be able to figure out if the Service is running when the Activity is started. There are some other questions here about that, so I think I can figure that out (but feel free to offer advice). My real problem: if the Activity is running and the Service is started, I need a way for the Service to send messages to the Activity. Simple Strings and integers at this point - status messages mostly. The messages will not happen regularly, so I don't think polling the service is a good way to go if there is another way. I only want this communication when the Activity has been started by the user - I don't want to start the Activity from the Service. In other words, if you start the Activity and the Service is running, you will see some status messages in the Activity UI when something interesting happens. If you don't start the Activity, you will not see these messages (they're not that interesting). It seems like I should be able to determine if the Service is running, and if so, add the Activity as a listener. Then remove the Activity as a listener when the Activity pauses or stops. Is that actually possible? The only way I can figure out to do it is to have the Activity implement Parcelable and build an AIDL file so I can pass it through the Service's remote interface. That seems like overkill though, and I have no idea how the Activity should implement writeToParcel() / readFromParcel(). Is there an easier or better way? Thanks for any help.

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