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• Possible to capture the returned value from a Python list comprehension for use a condition?

  - by Joe

  I want to construct a value in a list comprehension, but also filter on that value. For example: [expensive_function(x) for x in generator where expensive_function(x) < 5] I want to avoid calling expensive_function twice per iteration. The generator may return an infinite series, and list comprehensions aren't lazily evaluated. So this wouldn't work: [y in [expensive_function(x) for x in generator where expensive_function(x)] where y < 5] I could write this another way, but it feels right for a list comprehension and I'm sure this is a common usage pattern (possible or not!).

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• Is there a way to determine the Variance of an Interface / Delegate in C# 4.0?

  - by BFree

  So now that we have generic Covariance and Contravariance on interfaces and delegates in C#, I was just curious if given a Type, you can figure out the covariance/contravariance of its generic arguments. I started trying to write my own implementation, which would look through all of the methods on a given type and see if the return types and or arguments match the types in the generic arguments. The problem is that even if I have this: public interface IFoo<T> { void DoSomething(T item); } using my logic, it LOOKS like it should be contravariant, but since we didn't actually specify: public interface IFoo<in T> { void DoSomething(T item); } (the in parameter) it isn't actually contravariant. Which leads to my question: Is there a way to determine the variance of generic parameters?

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• MD5 hash differences between Python and other file hashers

  - by Sam

  I have been doing a bit of programming in Python (still a n00b at it) and came across something odd. I made a small program to find the MD5 hash of a filename passed to it on the command line. I used a function I found here on SO. When I ran it against a file, I got a hash "58a...113". But when I ran Microsoft's FCIV or the md5sum.py in \Python26\Tools\Scripts\, I get a different hash, "591...ae6". The actual hashing part of the md5sum.py in Scripts is m = md5.new() while 1: data = fp.read(bufsize) if not data: break m.update(data) out.write('%s %s\n' % (m.hexdigest(), filename)) This looks functionally identical to the code in the function given in the other answer... What am I missing? (This is my first time posting to stackoverflow, please let me know if I am doing it wrong.)

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• XmlSerializer.Serialize doesn't save a file and doesn't throw an exception.

  - by Wodzu

  Hi guys. I am having problem with saving of my object. Take a look at this code: public void SerializeToXML(String FileName) { XmlSerializer fSerializer = new XmlSerializer(typeof(Configuration)); using (Stream fStream = new FileStream(FileName, FileMode.Create, FileAccess.Write, FileShare.None)) { fSerializer.Serialize(fStream, this); } } The problem is that when the user does not have rights to the location on hard disk, this function will not throw me any exception and do not save my file. For example saving to "C:\test.xml" act like nothing happened. And I would like to know if the file has not been saved and it would be good to know the reason why. I know that I could check if the file on given location exists and throw an exception manualy but shouldn't this be done by the XmlSerializer or FileStream itself? Thanks for your time

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• Performance implications of finalizers on JVM

  - by Alexey Romanov

  According to this post, in .Net, Finalizers are actually even worse than that. Besides that they run late (which is indeed a serious problem for many kinds of resources), they are also less powerful because they can only perform a subset of the operations allowed in a destructor (e.g., a finalizer cannot reliably use other objects, whereas a destructor can), and even when writing in that subset finalizers are extremely difficult to write correctly. And collecting finalizable objects is expensive: Each finalizable object, and the potentially huge graph of objects reachable from it, is promoted to the next GC generation, which makes it more expensive to collect by some large multiple. Does this also apply to JVMs in general and to HotSpot in particular?

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• GWT - RichTextArea - ScrollTo

  - by Yanick Rochon

  If I have an RichTextArea like this : RichTextArea rta = new RichTextArea(); rta.setHTML("<p id=\"foo\">Foo</p>....<p id=\"bar\">Bar</p>"); If I extend the RichTextArea class, how would be the proper way (cross-browser wise) to write a scrollTo() method? Ex: class RichTextAreaExt extends RichTextArea { ... public native void scrollTo(String element) /*-{ // the underlaying DOMElement is an iframe, so.... }-*/; ... } Thanks!

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• compute mean in python for a generator

  - by nmaxwell

  Hi, I'm doing some statistics work, I have a (large) collection of random numbers to compute the mean of, I'd like to work with generators, because I just need to compute the mean, so I don't need to store the numbers. The problem is that numpy.mean breaks if you pass it a generator. I can write a simple function to do what I want, but I'm wondering if there's a proper, built-in way to do this? It would be nice if I could say "sum(values)/len(values)", but len doesn't work for genetators, and sum already consumed values. here's an example: import numpy def my_mean(values): n = 0 Sum = 0.0 try: while True: Sum += next(values) n += 1 except StopIteration: pass return float(Sum)/n X = [k for k in range(1,7)] Y = (k for k in range(1,7)) print numpy.mean(X) print my_mean(Y) these both give the same, correct, answer, buy my_mean doesn't work for lists, and numpy.mean doesn't work for generators. I really like the idea of working with generators, but details like this seem to spoil things. thanks for any help -nick

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• Redirected wikipedia request

  - by Le_Coeur

  Hi people, i need to write a program, that can redirect's http://localhost:8080 to en.wikipedia.org, it seems to be easy, but i have some problems(only with wikipedia with another sites works good). I make url to wikipedia: URL url = new URL("http", "en.wikipedia.org", 80, "/wiki"); than URLConnection, extract headers, and when i want connection.getInputStream(), i received message 404 Not Found. So i have tried some hack for host header, because in this way host header is localhost:8080, therefor i have tried to change host header to wikipedia, and it works, but after request in browser http://localhost:8080 wikipedia opens, but url in browser changes to en.wikipedia.org, but i want proceed with localhost :)

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• jQuery select number of tags

  - by ninumedia

  I have multiple comment ids I want to reset to a default value. Ex: <a id="comments_inner_toggle_45">example 1</a> <a id="comments_inner_toggle_608">example 2</a> <a id="comments_inner_toggle_28">example 3</a> ... How can I write the correct tag in jQuery to select every tag with an id of "comments_inner_toggle_" and perform some operation on it? I think it's something similar to: $('a[id|=comments_inner_toggle_]').whatever This is wrong however because the code above will only match the tag with "comments_inner_toggle_" and not with a number appended at the end. How can I fix this? thanks for the help! :)

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• Java Programming Homework

  - by user1427476

  Write a program to read in a file containing the names of the employ of a company and store them in an array of Strings named Employ []. Read another file containing the Salaries of each employ written in the same order and store them in another array of integers named salary[] (contents of both files are shown below). Finally create a file stating for example. Mr. XYZ receive $75,500.00 per year (Note that salary is stored as integer but displayed here as double with a comma separating thousands. This formatting needs to be done using DecimalFormat Class)

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• C++: Best text accumulator

  - by MInner

  Text gets accumulates piecemeal before being sent to client. Now we use own class that allocates memory for each piece as char massive. (Anyway, works like char[][] + std::list<char*>). Then we build the whole string, convert it into std::sting and then create boost::asio::streambuf using it. That's slow enough, I assume. Correct me if I'm wrong. I know, in many cases simple FILE type from stdio.h is used. How does it works? Allocates memory at every write into it. So, is it faster and is there any way to read into boost::asio::streambuf from FILE?

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• supply inputs to python unittests

  - by zubin71

  I`m relatively new to the concept of unit-testing and have very little experience in the same. I have been looking at lots of articles on how to write unit-tests; however, I still have difficulty in writing tests where conditions like the following arise:- Test user Input. Test input read from a file. Test input read from an environment variable. Itd be great if someone could show me how to approach the above mentioned scenarios; itd still be awesome if you could point me to a few docs/articles/blog posts which I could read.

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• INSERT INTO statement that copies rows and auto-increments non-identity key ID column

  - by AmoebaMan17

  Given a table that has three columns ID (Primary Key, not-autoincrementing) GroupID SomeValue I am trying to write a single SQL INSERT INTO statement that will make a copy of every row that has one GroupID into a new GroupID. Example beginning table: ID | GroupID | SomeValue ------------------------ 1 | 1 | a 2 | 1 | b Goal after I run a simple INSERT INTO statement: ID | GroupID | SomeValue ------------------------ 1 | 1 | a 2 | 1 | b 3 | 2 | a 4 | 2 | b I thought I could do something like: INSERT INTO MyTable ( [ID] ,[GroupID] ,[SomeValue] ) ( SELECT (SELECT MAX(ID) + 1 FROM MyTable) ,@NewGroupID ,[SomeValue] FROM MyTable WHERE ID = @OriginalGroupID ) This causes a PrimaryKey violation since it will end up reusing the same Max(ID)+1 value multiple times as it seems. Is my only recourse to a bunch of INSERT statements in a T-SQL WHILE statement that has an incrementing Counter value? I also don't have the option of turning the ID into an auto-incrementing Identity column since that would breaking code I don't have source for.

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• Operator() as a subscript (C++)

  - by Ivan Gromov

  I use operator() as a subscript operator this way: double CVector::operator() (int i) const { if (i >= 0 && i < this->size) return this->data[i]; else return 0; } double& CVector::operator() (int i) { return (this->data[i]); } It works when I get values, but I get an error when I try to write assign a value using a(i) = 1; UPD: Error text: Unhandled exception at 0x651cf54a (msvcr100d.dll) in CG.exe: 0xC0000005: Access violation reading location 0xccccccc0.

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• What are block expressions actually good for?

  - by Helper Method

  I just solved the first problem from Project Euler in JavaFX for the fun of it and wondered what block expressions are actually good for? Why are they superior to functions? Is it the because of the narrowed scope? Less to write? Performance? Here's the Euler example. I used a block here but I don't know if it actually makes sense // sums up all number from low to high exclusive which are divisible by a or b function sumDivisibleBy(a: Integer, b: Integer, high: Integer) { def low = if (a <= b) a else b; def sum = { var result = 0; for (i in [low .. <high] where i mod 3 == 0 or i mod 5 == 0) { result += i } result } } Does a block makes sense here?

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• Why wouldn't I be able to establish a trust relationship for a SSL/TLS channel?

  - by Abe Miessler

  I have a piece of .NET code that is erroring out when it makes a call to HTTPWebRequest.GetRequestStream. Here is the error message: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel. I've read a few things that suggest that I might need a certificate on the machine running the code, but i'm not sure if that's true or how to do it. If I need to get a certificate, how do I do it? Code: var request = (HttpWebRequest)HttpWebRequest.Create(requestUrl); //my url request.Method = StringUtilities.ConvertToString(httpMethod); // Set the http method GET, POST, etc. if (postData != null) { request.ContentLength = postData.Length; request.ContentType = contentType; using (var dataStream = request.GetRequestStream()) { dataStream.Write(postData, 0, postData.Length); } }

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• How do I pass a function to NUnit Throws.Constraints?

  - by Serge Belov

  I'm trying to write some NUnit tests in F# and having trouble passing a function to the ThrowsConstraint. A distilled (non)working sample is below. open System.IO open NUnit.Framework [<TestFixture>] module Example = [<Test>] let foo() = let f = fun () -> File.GetAttributes("non-existing.file") Assert.That(f, Throws.TypeOf<FileNotFoundException>()) This compiles just fine but I get the following from the NUnit test runner: FsTest.Tests.Example.foo: System.ArgumentException : The actual value must be a TestDelegate but was f@11 Parameter name: actual While I'm able to work around the problem using ExpectedException attribute, my question is what is the correct way of using an F# function in this situation?

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• Exploring search options for PHP

  - by Joshua

  I have innoDB table using numerous foreign keys, but we just want to look up some basic info out of it. I've done some research but still lost. 1) How can I tell if my host has Sphinx installed already? I don't see it as an option for table storage method (i.e. innodb, myisam). 2) Zend_Search_Lucene, responsive enough for AJAX functionality of millions of records? 3) Mirror my innoDB with a myisam? Make every innodb transaction end with a write to the myisam, then use 1:1 lookups? How would I do this automagically? This should make MyISAM ACID-compliant and free(er) from corruption no? 4) PostgreSQL fulltext queries don't even look like SQL to me wtf, I don't have time to learn a new SQL syntax I need noob options 5) ???????????????????? This is high volume site on a decently-equipped VPS Thanks very much for any ideas.

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• Confusing Perl code

  - by titaniumdecoy

  I don't understand the last line of this function from Programming Perl 3e. Here's how you might write a function that does a kind of set intersection by returning a list of keys occurring in all the hashes passed to it: @common = inter( \%foo, \%bar, \%joe ); sub inter { my %seen; for my $href (@_) { while (my $k = each %$href) { $seen{$k}++; } } return grep { $seen{$_} == @_ } keys %seen; } I understand that %seen is a hash which maps each key to the number of times it was encountered in any of the hashes provided to the function.

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• How do I change a property's value based on a conditional in msbuild?

  - by Noel Kennedy

  I would like to change the value of a property if it is a certain value. In C# I would write: if(x=="NotAllowed") x="CorrectedValue; This is what I have so far, please don't laugh: <PropertyGroup> <BranchName>BranchNameNotSet</BranchName> </PropertyGroup> ///Other targets set BranchName <Target Name="CheckPropertiesHaveBeenSet"> <Error Condition="$(BranchName)==BranchNameNotSet" Text="Something has gone wrong.. branch name not entered"/> <When Condition="$(BranchName)==master"> <PropertyGroup> <BranchName>MasterBranch</BranchName> </PropertyGroup> </When> </Target>

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• Ruby not-empty? method

  - by klew

  I want to use expression: !([1,2,3] & [43,5]).empty? => false !([1,2,3] & [3,5]).empty? => true to check if two arrays contains at least one common value. And I wonder if there is a better way of doing it? Maybe something like: ([1,2,3] & [3,5]).non_empty? How to write non_empty? method?

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• How can I copy a queryset to a new model in django admin?

  - by user3806832

  I'm trying to write an action that allows the user to select the queryset and copy it to a new table. So: John, Mark, James, Tyler and Joe are in a table 1( called round 1) The user selects the action that say to "move to next round" and those same instances that were chosen are now also in the table for "round 2". I started trying with an action but don't really know where to go from here: def Round_2(modeladmin, request, queryset): For X in queryset: X.pk = None perform.short_description = "Move to Round 2" How can I copy them to the next table with all of their information (pk doesn't have to be the same)? Thanks

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• Decoding and caching json every 60 minutes

  - by Gary

  Hi, How do I do this on a php webpage? I want to get and decode a json string and display the results as html on my page, however, I don't want it hotlinking back to the source. If I could write the decoded string to a txt file say weather.txt on the server and keep the html formatting and do it so that the page won't fetch the json script until 60 minutes has passed since the last time it was fetched regardless of how many times the page is opened during that 60 minute period and the weather.txt is viewed. All I can come up with is a simple script that hotlinks, everything else I have tried simply failed. $file = file_get_contents('http://sample.com/weather'); $out = (json_decode($file)); echo $out-mainText; Will appreciate any help with this.

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• When to use Vanilla Javascript vs. jQuery?

  - by jondavidjohn

  I have noticed while monitoring/attempting to answer common jQuery questions, that there are certain practices using javascript, instead of jQuery, that actually enable you to write less and do ... well the same amount. And may also yield performance benefits. A specific example $(this) vs this Inside a click event referencing the clicked objects id jQuery $(this).attr("id"); Javascript this.id; Are there any other common practices like this? Where certain Javascript operations could be accomplished easier, without bringing jQuery into the mix. Or is this a rare case? (of a jQuery "shortcut" actually requiring more code) EDIT : While I appreciate the answers regarding jQuery vs. plain javascript performance, I am actually looking for much more quantitative answers. While using jQuery, instances where one would actually be better off (readability/compactness) to use plain javascript instead of using $(). In addition to the example I gave in my original question.

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• In C#, What is <T> After a Method Declaration?

  - by Drew

  I'm a VB.Net guy. (because I have to be, because the person who signs my check says so. :P) I grew up in Java and I don't generally struggle to read or write in C# when I get the chance. I came across some syntax today that I have never seen, and that I can't seem to figure out. In the following method declaration, what does < T represent? static void Foo < T (params T[] x) I have seen used in conjunction with declaring generic collections and things, but I can't for the life of me figure out what it does for this method. In case it matters, I came across it when thinking about some C# brain teasers. The sixth teaser contains the entire code snippet.

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