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  • [Embedded Python] Invoking a method on an object

    - by jmucchiello
    Given a PyObject* pointing to a python object, how do I invoke one of the object methods? The documentation never gives an example of this: PyObject* obj = .... PyObject* args = Py_BuildValue("(s)", "An arg"); PyObject* method = PyWHATGOESHERE(obj, "foo"); PyObject* ret = PyWHATGOESHERE(obj, method, args); if (!ret) { // check error... } This would be the equivalent of >>> ret = obj.foo("An arg")

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  • Issuing multiple requests using HTTP/1.1 Pipelining

    - by Robert S. Barnes
    When using HTTP/1.1 Pipelining what does the standard say about issuing multiple requests without waiting for each request to complete? What do servers do in practice? I ask because I once tried writing a client which would issue a batch of GET requests for multiple files and remember getting errors. I wasn't sure if it was due to me incorrectly issuing the GET's or needing to wait for each individual request to finish before issuing the next GET.

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  • Details to log when starting an application

    - by Karl
    To help support and anyone who may use one of my applications I tend to log a few things during the application startup. Currently I log: Start Time App Name App Author App Version App Classpath Current working directory Java vendor Java version Max heap size Taking into consideration this application may be used / supported by a whole host of people can anyone think of any other vital details which we / others should log for good practice?

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  • Clojure for a lisp illiterate

    - by dbyrne
    I am a lifelong object-oriented programmer. My job is primarily java development, but I have experience in a number of languages. Ruby gave me my first real taste of functional programming. I loved the features Ruby borrowed from the functional paradigm such as closures and continuations. Eventually, I graduated to Scala. This has been a great way to gradually learn to approach non-trivial problems in a functional manner. Now I am interested in Clojure. I know all the sexy features that make it enticing (software transactional memory, macros, etc.), but I just can't get used to "thinking in lisp". I've seen Rich Hickey's screencasts aimed at java programmers, but they are geared towards explaining language features and not approaching real world problems. I am looking for any advice or resources which have made this transition easier for others.

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  • when to make a method static

    - by Don
    Hi, I'd like to know how people decide whether to define a method as static. I'm aware that a method can only be defined as static if it doesn't require access to instance fields. So lets say we have a method that does not access instance fields, do you always define such a method as static, or only if you need to call it statically (without a reference to an instance). Perhaps another way of asking the same question, is whether you use static or non-static as the default? Thanks, Don

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  • Why is this Scala example of implicit paremeter not working?

    - by Alex R
    simple REPL test... def g(a:Int)(implicit b:Int) = {a+b} Why do neither of these attempted usages work? 1. scala class A { var b:Int =8; var c = g(2) } :6: error: could not find implicit value for parameter b: Int class A { var b:Int =8; var c = g(2) } 2. scala class A(var b:Int) { var c = g(2) } :6: error: could not find implicit value for parameter b: Int class A(var b:Int) { var c = g(2) } ^ Thanks

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  • Why doesn't Java warn about a == "something"?

    - by Marius
    This might sound stupid, but why doesn't the Java compiler warn about the expression in the following if statement: String a = "something"; if(a == "something"){ System.out.println("a is equal to something"); }else{ System.out.println("a is not equal to something"); } I realize why the expression is untrue, but AFAIK, a can never be equal to the String literal "something". The compiler should realize this and at least warn me that I'm an idiot who is coding way to late at night.

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  • Determine if a Range contains a value

    - by Brad Dwyer
    I'm trying to figure out a way to determine if a value falls within a Range in Swift. Basically what I'm trying to do is adapt one of the examples switch statement examples to do something like this: let point = (1, -1) switch point { case let (x, y) where (0..5).contains(x): println("(\(x), \(y)) has an x val between 0 and 5.") default: println("This point has an x val outside 0 and 5.") } As far as I can tell, there isn't any built in way to do what my imaginary .contains method above does. So I tried to extend the Range class. I ended up running into issues with generics though. I can't extend Range<Int> so I had to try to extend Range itself. The closest I got was this but it doesn't work since >= and <= aren't defined for ForwardIndex extension Range { func contains(val:ForwardIndex) -> Bool { return val >= self.startIndex && val <= self.endIndex } } How would I go about adding a .contains method to Range? Or is there a better way to determine whether a value falls within a range? Edit2: This seems to work to extend Range extension Range { func contains(val:T) -> Bool { for x in self { if(x == val) { return true } } return false } } var a = 0..5 a.contains(3) // true a.contains(6) // false a.contains(-5) // false I am very interested in the ~= operator mentioned below though; looking into that now.

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  • How to evaluate text strings provided by sed/grep/whatever?

    - by T.J.
    This is for UNIX shell programming. It have to be supported by multiple UNIX platforms including Solaris, Linux, and AIX. I have this scenario -- I am to read from a text file a string that may or may not contain an environment variable that may or may not be defined. For example: <foo.bar> This error code was found: $(error_code) I have the following code: statement=$(sed -n $1'p' $messagefile) echo $echo_flag $statement $1 = line number supplied to this particular function/script. $messagefile = filename of log file. $echo_flag = "-e" in Linux, otherwise, empty. $(error_code) = 42. Instead of getting this when running: <foo.bar> This error code was found: 42 I still get this: <foo.bar> This error code was found: $(error_code) How exactly do I tell the shell script that the value of statement should be evaluated further beyond what sed have done?

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  • Capturing system command output as a string

    - by dreeves
    Perl and PHP do this with backticks. For example: $output = `ls`; This code returns a directory listing into the variable $output. A similar function, system("ls"), returns the operating system return code for the given command. I'm talking about a variant that returns whatever the command prints to stdout. (There are better ways to get the list of files in a directory; the example code is an example of this concept.) How do other languages do this? Is there a canonical name for this function? (I'm going with "backtick"; though maybe I could coin "syslurp".)

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  • How do software events work internally?

    - by Duddle
    Hello! I am a student of Computer Science and have learned many of the basic concepts of what is going on "under the hood" while a computer program is running. But recently I realized that I do not understand how software events work efficiently. In hardware, this is easy: instead of the processor "busy waiting" to see if something happened, the component sends an interrupt request. But how does this work in, for example, a mouse-over event? My guess is as follows: if the mouse sends a signal ("moved"), the operating system calculates its new position p, then checks what program is being drawn on the screen, tells that program position p, then the program itself checks what object is at p, checks if any event handlers are associated with said object and finally fires them. That sounds terribly inefficient to me, since a tiny mouse movement equates to a lot of cpu context switches (which I learned are relatively expensive). And then there are dozens of background applications that may want to do stuff of their own as well. Where is my intuition failing me? I realize that even "slow" 500MHz processors do 500 million operations per second, but still it seems too much work for such a simple event. Thanks in advance!

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  • Count the number of objects in an Image

    - by kunjaan
    I am investigating the possibility of image processing to identify certain objects and also count them in an image. I will be given a picture and I need to identify the number of boxes present in that image. Does anybody have any experience with any Machine Vision/ Image Processing libraries like ImageJ, Fiji, JAI, jMagick ,Java Vision Toolkit? Which do you think is best suited for the job? What do you guys suggest? If the APIs can be used from Java, it would be better. Thank you. Edit: I am dealing with warehouse brown boxes. Yes I am talking about regular photos. The source is usually a mobile phone picture.

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  • client-server application design

    - by nelly
    Hi, i want to create a client-server application using sockets on .net platform and being new to networking programming and i have a dilemma. The client will send data to server often and also the server will notify clients often. What is the best way to design it? should the server keep a thread to communicate with each client until it quits or just the clients send data to the server and it update the clients regularly(few seconds) or none of those? Some help would be great. Thanks guys.

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  • C# logic order and compiler behavior

    - by Terrapin
    In C#, (and feel free to answer for other languages), what order does the runtime evaluate a logic statement? Example: DataTable myDt = new DataTable(); if (myDt != null && myDt.Rows.Count > 0) { //do some stuff with myDt } Which statement does the runtime evaluate first - myDt != null or: myDt.Rows.Count > 0 ? Is there a time when the compiler would ever evaluate the statement backwards? Perhaps when an "OR" operator is involved?

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  • How to pass non-fatal warnings from a library

    - by wRAR
    A library function parses a file and returns an object. If a parser encounters unknown data, missing values etc., it shouldn't throw an exception and stop parsing (because this is not fatal), but there should be a way to pass information about these things to a caller (so that warnings can be displayed in the UI, for example). How can these warning be returned? I'm thinking of passing a callback function/object into the library, are there any other possible solutions?

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  • Where can I find documentation for Scala's delayed function calls?

    - by Geo
    I saw a delayed example in David Pollak's "Beginning Scala". I tried to adapt that, by trial and error. Here's what I have: def sayhello() = { println("hello") } def delaying(t: => Unit):Unit = { println("before call") t println("after call") } delaying(sayhello()) How would you delay a function/method that takes parameters? Why can't I use parantheses when I call t? Where can I find more documentation on delaying functions?

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  • How it is called when write or read return less that requested?

    - by Vi
    What term should I use to describe situations (or bugs in software) caused by read, write, send, recv doing less work than expected? For example, write(fd, "123456", 6); may return 3 and we need to write "456" to finish our work. I expect any good program should do all their reads and writes in a loop until without relying that write will write everything. Am I right? /* Implemented simple FUSE filesystem which only allows reading and writing with small buffers, very often returning that it is written less bytes that in a buffer. Some programs work, some not. Are them buggy? */

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  • Data storage advice needed: Best way to store location + time data?

    - by sobedai
    I have a project in mind that will require the majority of queries to be keyed off of lat/long as well as date + time. Initially, I was thinking of a standard RDBMS where lat, long, and the datetime field are properly indexed. Then, I began thinking of a document based system where the document was essentially a timestamp and each document has lat/long with in it. Each document could have n objects associated with it. I'm looking for advice on what would be the best type of storage engine for this sort of thing is - which of the above idea would be better or if there is something else completely that is the ideal solution. Thanks

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  • Simple integer encryption

    - by tloflin
    Is there a simple algorithm to encrypt integers? That is, a function E(i,k) that accepts an n-bit integer and a key (of any type) and produces another, unrelated n-bit integer that, when fed into a second function D(i,k) (along with the key) produces the original integer? Obviously there are some simple reversible operations you can perform, but they all seem to produce clearly related outputs (e.g. consecutive inputs lead to consecutive outputs). Also, of course, there are cryptographically strong standard algorithms, but they don't produce small enough outputs (e.g. 32-bit). I know any 32-bit cryptography can be brute-forced, but I'm not looking for something cryptographically strong, just something that looks random. Theoretically speaking it should be possible; after all, I could just create a dictionary by randomly pairing every integer. But I was hoping for something a little less memory-intensive.

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  • How to have the controller change its behavior depending on the view?

    - by Ian Boyd
    If from one view a user enters some invalid data, e.g.:     E-mail: [email protected]     then i want the controller to: not place the data into the model color the text box reddish not allow the user to save But it's possible that if the user enters the same invalid data in a different view i want the controller to: place the data into the model color the text box reddish allow the user to save But it's possible that if the user enters the same invalid data in a different view i want the controller to: place the data into the model color the text box bluish allow the user to save And it's possible that another view will: place the data into the model leave the text box uncolored allow the user to save And it's possible that another view will: auto-correct the data, placing it into the model color the text-box reddish allow the user to have And it's possible for another view to: auto-correct the data, placing it into the model update the view with the new data color the text-box bluish allow the user to save [ad infinitum] Without using n-controllers for n-views, how do i do this?

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  • Can I use part of MD5 hash for data identification?

    - by sharptooth
    I use MD5 hash for identifying files with unknown origin. No attacker here, so I don't care that MD5 has been broken and one can intendedly generate collisions. My problem is I need to provide logging so that different problems are diagnosed easier. If I log every hash as a hex string that's too long, inconvenient and looks ugly, so I'd like to shorten the hash string. Now I know that just taking a small part of a GUID is a very bad idea - GUIDs are designed to be unique, but part of them are not. Is the same true for MD5 - can I take say first 4 bytes of MD5 and assume that I only get collision probability higher due to the reduced number of bytes compared to the original hash?

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