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• In elisp is there a difference between the regex [\\]documentclass and \\documentclass?

  - by mcheema

  I was playing around with the rx function for generating regular expressions from sexps in ELISP but couldn't figure out how to generate the regular expression "\\documentclass" for use in org-export-latex-classes: (rx "\\documentclass") (rx "\\" "documentclass") (rx (char "\\") "documentclass") Which when evaluated give respectively the following outputs: "\\\\documentclass" "\\\\documentclass" "[\\]documentclass" Is "\\documentclass" equivalent to "[\\]documentclass"?---I think it is, but am not sure. Can I generate the former using rx? Edit: Whilst the question was valid I realize my motivation was not; because org-export-latex-classes use strings not regular expressions.

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• How to match parameter names in an expression?

  - by burak ozdogan

  Hi, I have a set of expressions representing some formula with some parameters inside. Like: [parameter1] * [parameter2] * [multiplier] And many others like this. I want to use a regular expression so that I can get a list of strings (List<string>) which will have the following inside: [paramter1] [paramter2] [multiplier] I am not using regular expressions so often; if you have already used something like this I would appreciate if you can share. Thanks!

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• Xpath visualization

  - by JavaRocky

  I am looking for a XML tool which does the following things. Allows me to enter xpath expressions and highlights the nodes selected Assists me in creating complex xpath expressions. What are other people using out there? I've used something from source forge but it only selects one matched node.

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• Red Hat Yum not working out of the box?

  - by Tucker

  I have a server runnning Red Hat Enterprise Linux v5.6 in the cloud. My project constraints do not allow me to use another OS. When I created the cloud server, I was able to SSH into it and access the shell. I next ran the command: sudo yum update But the command failed. About a month ago I created another server with the same machine image and didn't have that error. Why is it failing now? The following is the terminal output sudo yum update Loaded plugins: security Repository rhel-server is listed more than once in the configuration Traceback (most recent call last): File "/usr/bin/yum", line 29, in ? yummain.user_main(sys.argv[1:], exit_code=True) File "/usr/share/yum-cli/yummain.py", line 309, in user_main errcode = main(args) File "/usr/share/yum-cli/yummain.py", line 178, in main result, resultmsgs = base.doCommands() File "/usr/share/yum-cli/cli.py", line 345, in doCommands self._getTs(needTsRemove) File "/usr/lib/python2.4/site-packages/yum/depsolve.py", line 101, in _getTs self._getTsInfo(remove_only) File "/usr/lib/python2.4/site-packages/yum/depsolve.py", line 112, in _getTsInfo pkgSack = self.pkgSack File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 662, in <lambda> pkgSack = property(fget=lambda self: self._getSacks(), File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 502, in _getSacks self.repos.populateSack(which=repos) File "/usr/lib/python2.4/site-packages/yum/repos.py", line 260, in populateSack sack.populate(repo, mdtype, callback, cacheonly) File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 168, in populate if self._check_db_version(repo, mydbtype): File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 226, in _check_db_version return repo._check_db_version(mdtype) File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1233, in _check_db_version repoXML = self.repoXML File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1406, in <lambda> repoXML = property(fget=lambda self: self._getRepoXML(), File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1398, in _getRepoXML self._loadRepoXML(text=self) File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1388, in _loadRepoXML return self._groupLoadRepoXML(text, ["primary"]) File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1372, in _groupLoadRepoXML if self._commonLoadRepoXML(text): File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1208, in _commonLoadRepoXML result = self._getFileRepoXML(local, text) File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 989, in _getFileRepoXML cache=self.http_caching == 'all') File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 826, in _getFile http_headers=headers, File "/usr/lib/python2.4/site-packages/urlgrabber/mirror.py", line 412, in urlgrab return self._mirror_try(func, url, kw) File "/usr/lib/python2.4/site-packages/urlgrabber/mirror.py", line 398, in _mirror_try return func_ref( *(fullurl,), **kwargs ) File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 936, in urlgrab return self._retry(opts, retryfunc, url, filename) File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 854, in _retry r = apply(func, (opts,) + args, {}) File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 922, in retryfunc fo = URLGrabberFileObject(url, filename, opts) File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 1010, in __init__ self._do_open() File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 1093, in _do_open fo, hdr = self._make_request(req, opener) File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 1202, in _make_request fo = opener.open(req) File "/usr/lib64/python2.4/urllib2.py", line 358, in open response = self._open(req, data) File "/usr/lib64/python2.4/urllib2.py", line 376, in _open '_open', req) File "/usr/lib64/python2.4/urllib2.py", line 337, in _call_chain result = func(*args) File "/usr/lib64/python2.4/site-packages/M2Crypto/m2urllib2.py", line 82, in https_open h.request(req.get_method(), req.get_selector(), req.data, headers) File "/usr/lib64/python2.4/httplib.py", line 810, in request self._send_request(method, url, body, headers) File "/usr/lib64/python2.4/httplib.py", line 833, in _send_request self.endheaders() File "/usr/lib64/python2.4/httplib.py", line 804, in endheaders self._send_output() File "/usr/lib64/python2.4/httplib.py", line 685, in _send_output self.send(msg) File "/usr/lib64/python2.4/httplib.py", line 652, in send self.connect() File "/usr/lib64/python2.4/site-packages/M2Crypto/httpslib.py", line 47, in connect self.sock.connect((self.host, self.port)) File "/usr/lib64/python2.4/site-packages/M2Crypto/SSL/Connection.py", line 174, in connect ret = self.connect_ssl() File "/usr/lib64/python2.4/site-packages/M2Crypto/SSL/Connection.py", line 167, in connect_ssl return m2.ssl_connect(self.ssl, self._timeout) M2Crypto.SSL.SSLError: certificate verify failed

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• C#: System.Collections.Concurrent.ConcurrentQueue vs. Queue

  - by James Michael Hare

  I love new toys, so of course when .NET 4.0 came out I felt like the proverbial kid in the candy store!  Now, some people get all excited about the IDE and it’s new features or about changes to WPF and Silver Light and yes, those are all very fine and grand.  But me, I get all excited about things that tend to affect my life on the backside of development.  That’s why when I heard there were going to be concurrent container implementations in the latest version of .NET I was salivating like Pavlov’s dog at the dinner bell. They seem so simple, really, that one could easily overlook them.  Essentially they are implementations of containers (many that mirror the generic collections, others are new) that have either been optimized with very efficient, limited, or no locking but are still completely thread safe -- and I just had to see what kind of an improvement that would translate into. Since part of my job as a solutions architect here where I work is to help design, develop, and maintain the systems that process tons of requests each second, the thought of extremely efficient thread-safe containers was extremely appealing.  Of course, they also rolled out a whole parallel development framework which I won’t get into in this post but will cover bits and pieces of as time goes by. This time, I was mainly curious as to how well these new concurrent containers would perform compared to areas in our code where we manually synchronize them using lock or some other mechanism.  So I set about to run a processing test with a series of producers and consumers that would be either processing a traditional System.Collections.Generic.Queue or a System.Collection.Concurrent.ConcurrentQueue. Now, I wanted to keep the code as common as possible to make sure that the only variance was the container, so I created a test Producer and a test Consumer.  The test Producer takes an Action<string> delegate which is responsible for taking a string and placing it on whichever queue we’re testing in a thread-safe manner: 1: internal class Producer 2: { 3: public int Iterations { get; set; } 4: public Action<string> ProduceDelegate { get; set; } 5: 6: public void Produce() 7: { 8: for (int i = 0; i < Iterations; i++) 9: { 10: ProduceDelegate(“Hello”); 11: } 12: } 13: } Then likewise, I created a consumer that took a Func<string> that would read from whichever queue we’re testing and return either the string if data exists or null if not.  Then, if the item doesn’t exist, it will do a 10 ms wait before testing again.  Once all the producers are done and join the main thread, a flag will be set in each of the consumers to tell them once the queue is empty they can shut down since no other data is coming: 1: internal class Consumer 2: { 3: public Func<string> ConsumeDelegate { get; set; } 4: public bool HaltWhenEmpty { get; set; } 5: 6: public void Consume() 7: { 8: bool processing = true; 9: 10: while (processing) 11: { 12: string result = ConsumeDelegate(); 13: 14: if(result == null) 15: { 16: if (HaltWhenEmpty) 17: { 18: processing = false; 19: } 20: else 21: { 22: Thread.Sleep(TimeSpan.FromMilliseconds(10)); 23: } 24: } 25: else 26: { 27: DoWork(); // do something non-trivial so consumers lag behind a bit 28: } 29: } 30: } 31: } Okay, now that we’ve done that, we can launch threads of varying numbers using lambdas for each different method of production/consumption.  First let's look at the lambdas for a typical System.Collections.Generics.Queue with locking: 1: // lambda for putting to typical Queue with locking... 2: var productionDelegate = s => 3: { 4: lock (_mutex) 5: { 6: _mutexQueue.Enqueue(s); 7: } 8: }; 9:  10: // and lambda for typical getting from Queue with locking... 11: var consumptionDelegate = () => 12: { 13: lock (_mutex) 14: { 15: if (_mutexQueue.Count > 0) 16: { 17: return _mutexQueue.Dequeue(); 18: } 19: } 20: return null; 21: }; Nothing new or interesting here.  Just typical locks on an internal object instance.  Now let's look at using a ConcurrentQueue from the System.Collections.Concurrent library: 1: // lambda for putting to a ConcurrentQueue, notice it needs no locking! 2: var productionDelegate = s => 3: { 4: _concurrentQueue.Enqueue(s); 5: }; 6:  7: // lambda for getting from a ConcurrentQueue, once again, no locking required. 8: var consumptionDelegate = () => 9: { 10: string s; 11: return _concurrentQueue.TryDequeue(out s) ? s : null; 12: }; So I pass each of these lambdas and the number of producer and consumers threads to launch and take a look at the timing results.  Basically I’m timing from the time all threads start and begin producing/consuming to the time that all threads rejoin.  I won't bore you with the test code, basically it just launches code that creates the producers and consumers and launches them in their own threads, then waits for them all to rejoin.  The following are the timings from the start of all threads to the Join() on all threads completing.  The producers create 10,000,000 items evenly between themselves and then when all producers are done they trigger the consumers to stop once the queue is empty. These are the results in milliseconds from the ordinary Queue with locking: 1: Consumers Producers 1 2 3 Time (ms) 2: ---------- ---------- ------ ------ ------ --------- 3: 1 1 4284 5153 4226 4554.33 4: 10 10 4044 3831 5010 4295.00 5: 100 100 5497 5378 5612 5495.67 6: 1000 1000 24234 25409 27160 25601.00 And the following are the results in milliseconds from the ConcurrentQueue with no locking necessary: 1: Consumers Producers 1 2 3 Time (ms) 2: ---------- ---------- ------ ------ ------ --------- 3: 1 1 3647 3643 3718 3669.33 4: 10 10 2311 2136 2142 2196.33 5: 100 100 2480 2416 2190 2362.00 6: 1000 1000 7289 6897 7061 7082.33 Note that even though obviously 2000 threads is quite extreme, the concurrent queue actually scales really well, whereas the traditional queue with simple locking scales much more poorly. I love the new concurrent collections, they look so much simpler without littering your code with the locking logic, and they perform much better.  All in all, a great new toy to add to your arsenal of multi-threaded processing!

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• ASP.NET MVC 3: Implicit and Explicit code nuggets with Razor

  - by ScottGu

  This is another in a series of posts I’m doing that cover some of the new ASP.NET MVC 3 features: New @model keyword in Razor (Oct 19th) Layouts with Razor (Oct 22nd) Server-Side Comments with Razor (Nov 12th) Razor’s @: and <text> syntax (Dec 15th) Implicit and Explicit code nuggets with Razor (today) In today’s post I’m going to discuss how Razor enables you to both implicitly and explicitly define code nuggets within your view templates, and walkthrough some code examples of each of them.  Fluid Coding with Razor ASP.NET MVC 3 ships with a new view-engine option called “Razor” (in addition to the existing .aspx view engine).  You can learn more about Razor, why we are introducing it, and the syntax it supports from my Introducing Razor blog post. Razor minimizes the number of characters and keystrokes required when writing a view template, and enables a fast, fluid coding workflow. Unlike most template syntaxes, you do not need to interrupt your coding to explicitly denote the start and end of server blocks within your HTML. The Razor parser is smart enough to infer this from your code. This enables a compact and expressive syntax which is clean, fast and fun to type. For example, the Razor snippet below can be used to iterate a collection of products and output a <ul> list of product names that link to their corresponding product pages: When run, the above code generates output like below: Notice above how we were able to embed two code nuggets within the content of the foreach loop.  One of them outputs the name of the Product, and the other embeds the ProductID within a hyperlink.  Notice that we didn’t have to explicitly wrap these code-nuggets - Razor was instead smart enough to implicitly identify where the code began and ended in both of these situations.  How Razor Enables Implicit Code Nuggets Razor does not define its own language.  Instead, the code you write within Razor code nuggets is standard C# or VB.  This allows you to re-use your existing language skills, and avoid having to learn a customized language grammar. The Razor parser has smarts built into it so that whenever possible you do not need to explicitly mark the end of C#/VB code nuggets you write.  This makes coding more fluid and productive, and enables a nice, clean, concise template syntax.  Below are a few scenarios that Razor supports where you can avoid having to explicitly mark the beginning/end of a code nugget, and instead have Razor implicitly identify the code nugget scope for you: Property Access Razor allows you to output a variable value, or a sub-property on a variable that is referenced via “dot” notation: You can also use “dot” notation to access sub-properties multiple levels deep: Array/Collection Indexing: Razor allows you to index into collections or arrays: Calling Methods: Razor also allows you to invoke methods: Notice how for all of the scenarios above how we did not have to explicitly end the code nugget.  Razor was able to implicitly identify the end of the code block for us. Razor’s Parsing Algorithm for Code Nuggets The below algorithm captures the core parsing logic we use to support “@” expressions within Razor, and to enable the implicit code nugget scenarios above: Parse an identifier - As soon as we see a character that isn't valid in a C# or VB identifier, we stop and move to step 2 Check for brackets - If we see "(" or "[", go to step 2.1., otherwise, go to step 3  Parse until the matching ")" or "]" (we track nested "()" and "[]" pairs and ignore "()[]" we see in strings or comments) Go back to step 2 Check for a "." - If we see one, go to step 3.1, otherwise, DO NOT ACCEPT THE "." as code, and go to step 4 If the character AFTER the "." is a valid identifier, accept the "." and go back to step 1, otherwise, go to step 4 Done! Differentiating between code and content Step 3.1 is a particularly interesting part of the above algorithm, and enables Razor to differentiate between scenarios where an identifier is being used as part of the code statement, and when it should instead be treated as static content: Notice how in the snippet above we have ? and ! characters at the end of our code nuggets.  These are both legal C# identifiers – but Razor is able to implicitly identify that they should be treated as static string content as opposed to being part of the code expression because there is whitespace after them.  This is pretty cool and saves us keystrokes. Explicit Code Nuggets in Razor Razor is smart enough to implicitly identify a lot of code nugget scenarios.  But there are still times when you want/need to be more explicit in how you scope the code nugget expression.  The @(expression) syntax allows you to do this: You can write any C#/VB code statement you want within the @() syntax.  Razor will treat the wrapping () characters as the explicit scope of the code nugget statement.  Below are a few scenarios where we could use the explicit code nugget feature: Perform Arithmetic Calculation/Modification: You can perform arithmetic calculations within an explicit code nugget: Appending Text to a Code Expression Result: You can use the explicit expression syntax to append static text at the end of a code nugget without having to worry about it being incorrectly parsed as code: Above we have embedded a code nugget within an <img> element’s src attribute.  It allows us to link to images with URLs like “/Images/Beverages.jpg”.  Without the explicit parenthesis, Razor would have looked for a “.jpg” property on the CategoryName (and raised an error).  By being explicit we can clearly denote where the code ends and the text begins. Using Generics and Lambdas Explicit expressions also allow us to use generic types and generic methods within code expressions – and enable us to avoid the <> characters in generics from being ambiguous with tag elements. One More Thing….Intellisense within Attributes We have used code nuggets within HTML attributes in several of the examples above.  One nice feature supported by the Razor code editor within Visual Studio is the ability to still get VB/C# intellisense when doing this. Below is an example of C# code intellisense when using an implicit code nugget within an <a> href=”” attribute: Below is an example of C# code intellisense when using an explicit code nugget embedded in the middle of a <img> src=”” attribute: Notice how we are getting full code intellisense for both scenarios – despite the fact that the code expression is embedded within an HTML attribute (something the existing .aspx code editor doesn’t support).  This makes writing code even easier, and ensures that you can take advantage of intellisense everywhere. Summary Razor enables a clean and concise templating syntax that enables a very fluid coding workflow.  Razor’s ability to implicitly scope code nuggets reduces the amount of typing you need to perform, and leaves you with really clean code. When necessary, you can also explicitly scope code expressions using a @(expression) syntax to provide greater clarity around your intent, as well as to disambiguate code statements from static markup. Hope this helps, Scott P.S. In addition to blogging, I am also now using Twitter for quick updates and to share links. Follow me at: twitter.com/scottgu

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• We've completed the first iteration

  - by CliveT

  There are a lot of features in C# that are implemented by the compiler and not by the underlying platform. One such feature is a lambda expression. Since local variables cannot be accessed once the current method activation finishes, the compiler has to go out of its way to generate a new class which acts as a home for any variable whose lifetime needs to be extended past the activation of the procedure. Take the following example:     Random generator = new Random();     Func func = () = generator.Next(10); In this case, the compiler generates a new class called c_DisplayClass1 which is marked with the CompilerGenerated attribute. [CompilerGenerated] private sealed class c__DisplayClass1 {     // Fields     public Random generator;     // Methods     public int b__0()     {         return this.generator.Next(10);     } } Two quick comments on this: (i)    A display was the means that compilers for languages like Algol recorded the various lexical contours of the nested procedure activations on the stack. I imagine that this is what has led to the name. (ii)    It is a shame that the same attribute is used to mark all compiler generated classes as it makes it hard to figure out what they are being used for. Indeed, you could imagine optimisations that the runtime could perform if it knew that classes corresponded to certain high level concepts. We can see that the local variable generator has been turned into a field in the class, and the body of the lambda expression has been turned into a method of the new class. The code that builds the Func object simply constructs an instance of this class and initialises the fields to their initial values.     c__DisplayClass1 class2 = new c__DisplayClass1();     class2.generator = new Random();     Func func = new Func(class2.b__0); Reflector already contains code to spot this pattern of code and reproduce the form containing the lambda expression, so this is example is correctly decompiled. The use of compiler generated code is even more spectacular in the case of iterators. C# introduced the idea of a method that could automatically store its state between calls, so that it can pick up where it left off. The code can express the logical flow with yield return and yield break denoting places where the method should return a particular value and be prepared to resume.         {             yield return 1;             yield return 2;             yield return 3;         } Of course, there was already a .NET pattern for expressing the idea of returning a sequence of values with the computation proceeding lazily (in the sense that the work for the next value is executed on demand). This is expressed by the IEnumerable interface with its Current property for fetching the current value and the MoveNext method for forcing the computation of the next value. The sequence is terminated when this method returns false. The C# compiler links these two ideas together so that an IEnumerator returning method using the yield keyword causes the compiler to produce the implementation of an Iterator. Take the following piece of code.         IEnumerable GetItems()         {             yield return 1;             yield return 2;             yield return 3;         } The compiler implements this by defining a new class that implements a state machine. This has an integer state that records which yield point we should go to if we are resumed. It also has a field that records the Current value of the enumerator and a field for recording the thread. This latter value is used for optimising the creation of iterator instances. [CompilerGenerated] private sealed class d__0 : IEnumerable, IEnumerable, IEnumerator, IEnumerator, IDisposable {     // Fields     private int 1__state;     private int 2__current;     public Program 4__this;     private int l__initialThreadId; The body gets converted into the code to construct and initialize this new class. private IEnumerable GetItems() {     d__0 d__ = new d__0(-2);     d__.4__this = this;     return d__; } When the class is constructed we set the state, which was passed through as -2 and the current thread. public d__0(int 1__state) {     this.1__state = 1__state;     this.l__initialThreadId = Thread.CurrentThread.ManagedThreadId; } The state needs to be set to 0 to represent a valid enumerator and this is done in the GetEnumerator method which optimises for the usual case where the returned enumerator is only used once. IEnumerator IEnumerable.GetEnumerator() {     if ((Thread.CurrentThread.ManagedThreadId == this.l__initialThreadId)               && (this.1__state == -2))     {         this.1__state = 0;         return this;     } The state machine itself is implemented inside the MoveNext method. private bool MoveNext() {     switch (this.1__state)     {         case 0:             this.1__state = -1;             this.2__current = 1;             this.1__state = 1;             return true;         case 1:             this.1__state = -1;             this.2__current = 2;             this.1__state = 2;             return true;         case 2:             this.1__state = -1;             this.2__current = 3;             this.1__state = 3;             return true;         case 3:             this.1__state = -1;             break;     }     return false; } At each stage, the current value of the state is used to determine how far we got, and then we generate the next value which we return after recording the next state. Finally we return false from the MoveNext to signify the end of the sequence. Of course, that example was really simple. The original method body didn't have any local variables. Any local variables need to live between the calls to MoveNext and so they need to be transformed into fields in much the same way that we did in the case of the lambda expression. More complicated MoveNext methods are required to deal with resources that need to be disposed when the iterator finishes, and sometimes the compiler uses a temporary variable to hold the return value. Why all of this explanation? We've implemented the de-compilation of iterators in the current EAP version of Reflector (7). This contrasts with previous version where all you could do was look at the MoveNext method and try to figure out the control flow. There's a fair amount of things we have to do. We have to spot the use of a CompilerGenerated class which implements the Enumerator pattern. We need to go to the class and figure out the fields corresponding to the local variables. We then need to go to the MoveNext method and try to break it into the various possible states and spot the state transitions. We can then take these pieces and put them back together into an object model that uses yield return to show the transition points. After that Reflector can carry on optimising using its usual optimisations. The pattern matching is currently a little too sensitive to changes in the code generation, and we only do a limited analysis of the MoveNext method to determine use of the compiler generated fields. In some ways, it is a pity that iterators are compiled away and there is no metadata that reflects the original intent. Without it, we are always going to dependent on our knowledge of the compiler's implementation. For example, we have noticed that the Async CTP changes the way that iterators are code generated, so we'll have to do some more work to support that. However, with that warning in place, we seem to do a reasonable job of decompiling the iterators that are built into the framework. Hopefully, the EAP will give us a chance to find examples where we don't spot the pattern correctly or regenerate the wrong code, and we can improve things. Please give it a go, and report any problems.

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• GPU Debugging with VS 11

  - by Daniel Moth

  With VS 11 Developer Preview we have invested tremendously in parallel debugging for both CPU (managed and native) and GPU debugging. I'll be doing a whole bunch of blog posts on those topics, and in this post I just wanted to get people started with GPU debugging, i.e. with debugging C++ AMP code. First I invite you to watch 6 minutes of a glimpse of the C++ AMP debugging experience though this video (ffw to minute 51:54, up until minute 59:16). Don't read the rest of this post, just go watch that video, ideally download the High Quality WMV. Summary GPU debugging essentially means debugging the lambda that you pass to the parallel_for_each call (plus any functions you call from the lambda, of course). CPU debugging means debugging all the code above and below the parallel_for_each call, i.e. all the code except the restrict(direct3d) lambda and the functions that it calls. With VS 11 you have to choose what debugger you want to use for a particular debugging session, CPU or GPU. So you can place breakpoints all over your code, then choose what debugger you want (CPU or GPU), and you'll only be able to hit breakpoints for the code type that the debugger engine understands – the remaining breakpoints will appear as unbound. If you want to hit the unbound breakpoints, you'd have to stop debugging, and start again with the other debugger. Sorry. We suck. We know. But once you are past that limitation, I think you'll find the experience truly rewarding – seriously! Switching debugger engines With the Developer Preview bits, one way to switch the debugger engine is through the project properties – see the screenshots that follow. This one is showing the CPU option selected, which is basically the default that you are all familiar with: This screenshot is showing the GPU option selected, by changing the debugger launcher (notice that this applies for both the local and remote case): You actually do not have to open the project properties just for switching the debugger engine, you can switch the selection from the toolbar in VS 11 Developer Preview too – see following screenshot (the effect is the same as if you opened the project properties and switched there) Breakpoint behavior Here are two screenshots, one showing a debugging session for CPU and the other a debugging session for GPU (notice the unbound breakpoints in each case) …and here is the GPU case (where we cannot bind the CPU breakpoints but can the GPU breakpoint, which is actually hit) Give C++ AMP debugging a try So to debug your C++ AMP code, pull down the drop down under the 'play' button to select the 'GPU C++ Direct3D Compute Debugger' menu option, then hit F5 (or the 'play' button itself). Then you can explore debugging by exploring the menus under the Debug and under the Debug->Windows menus. One way to do that exploration is through the C++ AMP debugging walkthrough on MSDN. Another way to explore the C++ AMP debugging experience, you can use the moth.cpp code file, which is what I used in my BUILD session debugger demo. Note that for my demo I was using the latest internal VS11 bits, so your experience with the Developer Preview bits won't be identical to what you saw me demonstrate, but it shouldn't be far off. Stay tuned for a lot more content on the parallel debugger in VS 11, both CPU and GPU, both managed and native. Comments about this post by Daniel Moth welcome at the original blog.

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• Get Exchange Online Mailbox Size in GB

  - by Brian Jackett

  As mentioned in my previous post I was recently working with a customer to get started with Exchange Online PowerShell commandlets.  In this post I wanted to follow up and show one example of a difference in output from commandlets in Exchange 2010 on-premises vs. Exchange Online.   Problem    The customer was interested in getting the size of mailboxes in GB.  For Exchange on-premises this is fairly easy.  A fellow PFE Gary Siepser wrote an article explaining how to accomplish this (click here).  Note that Gary’s script will not work when remoting from a local machine that doesn’t have the Exchange object model installed.  A similar type of scenario exists if you are executing PowerShell against Exchange Online.  The data type for TotalItemSize  being returned (ByteQuantifiedSize) exists in the Exchange namespace.  If the PowerShell session doesn’t have access to that namespace (or hasn’t loaded it) PowerShell works with an approximation of that data type.    The customer found a sample script on this TechNet article that they attempted to use (minor edits by me to fit on page and remove references to deleted item size.)   Get-Mailbox -ResultSize Unlimited | Get-MailboxStatistics | Select DisplayName,StorageLimitStatus, ` @{name="TotalItemSize (MB)"; expression={[math]::Round( ` ($_.TotalItemSize.Split("(")[1].Split(" ")[0].Replace(",","")/1MB),2)}}, ` ItemCount | Sort "TotalItemSize (MB)" -Descending | Export-CSV "C:\My Documents\All Mailboxes.csv" -NoTypeInformation     The script is targeted to Exchange 2010 but fails for Exchange Online.  In Exchange Online when referencing the TotalItemSize property though it does not have a Split method which ultimately causes the script to fail.   Solution    A simple solution would be to add a call to the ToString method off of the TotalItemSize property (in bold on line 5 below).   Get-Mailbox -ResultSize Unlimited | Get-MailboxStatistics | Select DisplayName,StorageLimitStatus, ` @{name="TotalItemSize (MB)"; expression={[math]::Round( ` ($_.TotalItemSize.ToString().Split("(")[1].Split(" ")[0].Replace(",","")/1MB),2)}}, ` ItemCount | Sort "TotalItemSize (MB)" -Descending | Export-CSV "C:\My Documents\All Mailboxes.csv" -NoTypeInformation      This fixes the script to run but the numerous string replacements and splits are an eye sore to me.  I attempted to simplify the string manipulation with a regular expression (more info on regular expressions in PowerShell click here).  The result is a workable script that does one nice feature of adding a new member to the mailbox statistics called TotalItemSizeInBytes.  With this member you can then convert into any byte level (KB, MB, GB, etc.) that suits your needs.  You can download the full version of this script below (includes commands to connect to Exchange Online session). $UserMailboxStats = Get-Mailbox -RecipientTypeDetails UserMailbox ` -ResultSize Unlimited | Get-MailboxStatistics $UserMailboxStats | Add-Member -MemberType ScriptProperty -Name TotalItemSizeInBytes ` -Value {$this.TotalItemSize -replace "(.*\()|,| [a-z]*\)", ""} $UserMailboxStats | Select-Object DisplayName,@{Name="TotalItemSize (GB)"; ` Expression={[math]::Round($_.TotalItemSizeInBytes/1GB,2)}}   Conclusion    Moving from on-premises to the cloud with PowerShell (and PowerShell remoting in general) can sometimes present some new challenges due to what you have access to.  This means that you must always test your code / scripts.  I still believe that not having to physically RDP to a server is a huge gain over some of the small hurdles you may encounter during the transition.  Scripting is the future of administration and makes you more valuable.  Hopefully this script and the concepts presented help you be a better admin / developer.         -Frog Out     Links The Get-MailboxStatistics Cmdlet, the TotalitemSize Property, and that pesky little “b” http://blogs.technet.com/b/gary/archive/2010/02/20/the-get-mailboxstatistics-cmdlet-the-totalitemsize-property-and-that-pesky-little-b.aspx   View Mailbox Sizes and Mailbox Quotas Using Windows PowerShell http://technet.microsoft.com/en-us/exchangelabshelp/gg576861#ViewAllMailboxes   Regular Expressions with Windows PowerShell http://www.regular-expressions.info/powershell.html   “I don’t always test my code…” image http://blogs.pinkelephant.com/images/uploads/conferences/I-dont-always-test-my-code-But-when-I-do-I-do-it-in-production.jpg   The One Thing: Brian Jackett and SharePoint 2010 http://www.youtube.com/watch?v=Sg_h66HMP9o

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• Is this Hybrid of Interface / Composition kosher?

  - by paul

  I'm working on a project in which I'm considering using a hybrid of interfaces and composition as a single thing. What I mean by this is having a contain*ee* class be used as a front for functionality implemented in a contain*er* class, where the container exposes the containee as a public property. Example (pseudocode): class Visibility(lambda doShow, lambda doHide, lambda isVisible) public method Show() {...} public method Hide() {...} public property IsVisible public event Shown public event Hidden class SomeClassWithVisibility private member visibility = new Visibility(doShow, doHide, isVisible) public property Visibility with get() = visibility private method doShow() {...} private method doHide() {...} private method isVisible() {...} There are three reasons I'm considering this: The language in which I'm working (F#) has some annoyances w.r.t. implementing interfaces the way I need to (unless I'm missing something) and this will help avoid a lot of boilerplate code. The containee classes could really be considered properties of the container class(es); i.e. there seems to be a fairly strong has-a relationship. The containee classes will likely implement code which would have been pretty much the same when implemented in all the container classes, so why not do it once in one place? In the above example, this would include managing and emitting the Shown/Hidden events. Does anyone see any isseus with this Composiface/Intersition method, or know of a better way? EDIT 2012.07.26 - It seems a little background information is warranted: Where I work, we have a bunch of application front-ends that have limited access to system resources -- they need access to these resources to fully function. To remedy this we have a back-end application that can access the needed resources, with which the front-ends can communicate. (There is an API written for the front-ends for accessing back-end functionality as though it were part of the front-end.) The back-end program is out of date and its functionality is incomplete. It has made the transition from company to company a couple of times and we can't even compile it anymore. So I'm trying to rewrite it in my spare time. I'm trying to update things to make a nice(r) interface/API for the front-ends (while allowing for backwards compatibility with older front-ends), hopefully something full of OOPy goodness. The thing is, I don't want to write the front-end API after I've written pretty much the same code in F# for implementing the back-end; so, what I'm planning on doing is applying attributes to classes/methods/properties that I would like to have code for in the API then generate this code from the F# assembly using reflection. The method outlined in this question is a possible alternative I'm considering instead of implementing straight interfaces on the classes in F# because they're kind of a bear: In order to access something of an interface that has been implemented in a class, you have to explicitly cast an instance of that class to the interface type. This would make things painful when getting calls from the front-ends. If you don't want to have to do this, you have to call out all of the interface's methods/properties again in the class, outside of the interface implementation (which is separate from regular class members), and call the implementation's members. This is basically repeating the same code, which is what I'm trying to avoid!

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• Looping Redirect with PyFacebook and Google App Engine

  - by Nick Gotch

  I have a Python Facebook project hosted on Google App Engine and use the following code to handle initialization of the Facebook API using PyFacebook. # Facebook Initialization def initialize_facebook(f): # Redirection handler def redirect(self, url): logger.info('Redirecting the user to: ' + url) self.response.headers.add_header("Cache-Control", "max-age=0") self.response.headers.add_header("Pragma", "no-cache") self.response.out.write('<html><head><script>parent.location.replace(\'' + url + '\');</script></head></html>') return 'Moved temporarily' auth_token = request.params.get('auth_token', None) fbapi = Facebook(settings['FACEBOOK_API_KEY'], settings['FACEBOOK_SECRET_KEY'], auth_token=auth_token) if not fbapi: logger.error('Facebook failed to initialize') if fbapi.check_session(request) or auth_token: pass else: logger.info('User not logged into Facebook') return lambda a: redirect(a, fbapi.get_login_url()) if fbapi.added: pass else: logger.info('User does not have ' + settings['FACEBOOK_APP_NAME'] + ' added') return lambda a: redirect(a, fbapi.get_add_url()) # Return the validated API logger.info('Facebook successfully initialized') return lambda a: f(a, fbapi=fbapi) I'm trying to set it up so that I can drop this decorator on any page handler method and verify that the user has everything set up correctly. The issue is that when the redirect handler gets called, it starts an infinite loop of redirection. I tried using an HTTP 302 redirection in place of the JavaScript but that kept failing too. Does anyone know what I can do to fix this? I saw this similar question but there are no answers.

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• PLT Scheme Memory

  - by Eric

  So I need some help with implementing a Make-memory program using Scheme. I need two messages 'write and 'read. So it would be like (mymem 'write 34 -116) and (mymem 'read 99) right? and (define mymem (make-memory 100)).....How would I implement this in scheme? using an Alist???I need some help coding it. I have this code which makes make-memory a procedure and when you run mymem you get ((99.0)) and what i need to do is recur this so i get an alist with dotted pairs to ((0.0)). So any suggestions on how to code this?? Does anyone have any ideas what I could do to recur and make messages Write and read?? (define make-memory (lambda (n) (letrec ((mem '()) (dump (display mem))) (lambda () (if (= n 0) (cons (cons n 0) mem) mem) (cons (cons (- n 1) 0) mem)) (lambda (msg loc val) (cond ((equal? msg 'read) (display (cons n val))(set! n (- n 1))) ((equal? msg 'write) (set! mem (cons val loc)) (set! n (- n 1)) (display mem))))))) (define mymem (make-memory 100)) Yes this is an assignment but I wrote this code. I just need some help or direction. And yes I do know about variable-length argument lists.

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• Java how can I add an accented "e" to a string?

  - by behrk2

  Hello, With the help of tucuxi from the existing post Java remove HTML from String without regular expressions I have built a method that will parse out any basic HTML tags from a string. Sometimes, however, the original string contains html hexadecimal characters like é (which is an accented e). I have started to add functionality which will translate these escaped characters into real characters. You're probably asking: Why not use regular expressions? Or a third party library? Unfortunately I cannot, as I am developing on a BlackBerry platform which does not support regular expressions and I have never been able to successfully add a third party library to my project. So, I have gotten to the point where any é is replaced with "e". My question now is, how do I add an actual 'accented e' to a string? Here is my code: public static String removeHTML(String synopsis) { char[] cs = synopsis.toCharArray(); String sb = new String(); boolean tag = false; for (int i = 0; i < cs.length; i++) { switch (cs[i]) { case '<': if (!tag) { tag = true; break; } case '>': if (tag) { tag = false; break; } case '&': char[] copyTo = new char[7]; System.arraycopy(cs, i, copyTo, 0, 7); String result = new String(copyTo); if (result.equals("&#x00E9")) { sb += "e"; } i += 7; break; default: if (!tag) sb += cs[i]; } } return sb.toString(); } Thanks!

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• What's wrong with this regex (VBScript/Javascript flavor)

  - by OtherMichael

  I'm trying to run a regular expression in VBA code that uses Microsoft VBScript Regular Expressions 5.5 (should be the same as JavaScript regex) regex: ^[0-9A-Z]?[0-9A-Z]{3}[A-Z]?([0-9A-Z]{6})-?([0-9])?$ input: X123A1234567 match: 123456 the six characters I'm interested in give a good match of 123456, ignoring the last (check) digit. Perfect. (The check digit is captured, but it's not a major concern to me). But when BOTH the optional portions are gone (they are optional) the match grabs the last digit GOOD input: 123A1234567 match: 123456 Leave in the optional middle alpha, take out the optional leading alpha, and we still get the good match of 123456 GOOD input: X1231234567 match: 123456 Leave in the optional leading alpha, take out the middle optional alpha, and we still get a good match of 123456 BAD input: 1231234567 match: 234567 Take out BOTH optional alphas, and we get a bad match of 234567 Have a looksee @ the regex testers on http://www.regular-expressions.info/javascriptexample.html or http://www.regular-expressions.info/vbscriptexample.html What am I missing, here? How can I get the regex to ignore the last digit when both optional alphas are missing? The regex is used to feed a lookup system, so that no matter what format the input data, we can match to a complete value.

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• LinqKit System.InvalidCastException When Invoking method-provided expression on member property.

  - by mdworkin

  Given a simple parent/child class structure. I want to use linqkit to apply a child lambda expression on the parent. I also want the Lambda expression to be provided by a utility method. public class Foo { public Bar Bar { get; set; } } public class Bar { public string Value { get; set; } public static Expression<Func<Bar, bool>> GetLambdaX() { return c => c.Value == "A"; } } ... Expression<Func<Foo, bool>> lx = c => Bar.GetLambdaX().Invoke(c.Bar); Console.WriteLine(lx.Expand()); The above code throws System.InvalidCastException: Unable to cast object of type 'System.Linq.Expressions.MethodCallExpression' to type 'System.Linq.Expressions.LambdaExpression'. at LinqKit.ExpressionExpander.VisitMethodCall(MethodCallExpression m) at LinqKit.ExpressionVisitor.Visit(Expression exp) at LinqKit.ExpressionVisitor.VisitLambda(LambdaExpression lambda) at LinqKit.ExpressionVisitor.Visit(Expression exp) at LinqKit.Extensions.Expand<TDelegate>(Expression`1 expr) .... Please help!

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• Creating a new workbook in Excel from Python breaks

  - by Marcelo Cantos

  I am trying to use the stock standard win32com approach to drive Excel 2007 from Python. However, when I try to create a new workbook, things go pear-shaped: Python 2.6.4 (r264:75706, Nov 3 2009, 13:23:17) [MSC v.1500 32 bit (Intel)] on win32 ... >>> import win32com.client >>> excel = win32com.client.Dispatch("Excel.Application") >>> wb = excel.Workbooks.Add() Traceback (most recent call last): File "<pyshell#3>", line 1, in <module> wb = excel.Workbooks.Add() File "C:\Python26\lib\site-packages\win32com\client\dynamic.py", line 467, in __getattr__ if self._olerepr_.mapFuncs.has_key(attr): return self._make_method_(attr) File "C:\Python26\lib\site-packages\win32com\client\dynamic.py", line 295, in _make_method_ methodCodeList = self._olerepr_.MakeFuncMethod(self._olerepr_.mapFuncs[name], methodName,0) File "C:\Python26\lib\site-packages\win32com\client\build.py", line 297, in MakeFuncMethod return self.MakeDispatchFuncMethod(entry, name, bMakeClass) File "C:\Python26\lib\site-packages\win32com\client\build.py", line 318, in MakeDispatchFuncMethod s = linePrefix + 'def ' + name + '(self' + BuildCallList(fdesc, names, defNamedOptArg, defNamedNotOptArg, defUnnamedArg, defOutArg) + '):' File "C:\Python26\lib\site-packages\win32com\client\build.py", line 604, in BuildCallList argName = MakePublicAttributeName(argName) File "C:\Python26\lib\site-packages\win32com\client\build.py", line 542, in MakePublicAttributeName return filter( lambda char: char in valid_identifier_chars, className) File "C:\Python26\lib\site-packages\win32com\client\build.py", line 542, in <lambda> return filter( lambda char: char in valid_identifier_chars, className) UnicodeDecodeError: 'ascii' codec can't decode byte 0x83 in position 52: ordinal not in range(128) >>> What is going wrong here? Have I done something silly, or is Python/win32com/Excel somehow broken?

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• "User Friendly" .net compatible Regex/Text matching tools?

  - by Binary Worrier

  Currently in our software we provide a hook where we call a DLL built by our clients to parse information out of documents we are processing (the DLL takes in some text (or a file) and returns a list of name/value pairs). e.g. We're given a Word doc or Text file to Archive. We do various things to the file, and call a DLL that will return "pertinent" information about the file. Among other things we store that "pertinent" data for posterity. What is considered "pertinent" depends on the client and the type of the document, we don't care, we get it and store it. I've been asked to develop a user friendly "something" that will allow a non-programmer user to "configure" how to get this data from a plain text document (<humor>The user story ends with the helpful suggestion/query "We could use regex for this?"</humor>) It's safe to assume that a list of regex's isn't going to cut this, I've written some of these parsers for customers, the regex's to do these would be hedious and some of them can't be done by regex's. Also one of the requirements above is "user friendly" which negates anything that has users seeing or editing regex expressions. As you can guess, I don't have a fortune of time to do this, and am wondering is there anything out there that I can plug in to our app that has a nice front end and does exactly what I need? :) No? Whadda mean no! . . . sigh Ok then failing that, anything out there that "visually" builds regex's and/or other pattern matching expressions, and then allows one to run those expressions against some text? The MS BRE will do what I want, but I need something prettier that looks less like code. Thanks guys,

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• Converting a Linq expression tree that relies on SqlMethods.Like() for use with the Entity Framework

  - by JohnnyO

  I recently switched from using Linq to Sql to the Entity Framework. One of the things that I've been really struggling with is getting a general purpose IQueryable extension method that was built for Linq to Sql to work with the Entity Framework. This extension method has a dependency on the Like() method of SqlMethods, which is Linq to Sql specific. What I really like about this extension method is that it allows me to dynamically construct a Sql Like statement on any object at runtime, by simply passing in a property name (as string) and a query clause (also as string). Such an extension method is very convenient for using grids like flexigrid or jqgrid. Here is the Linq to Sql version (taken from this tutorial: http://www.codeproject.com/KB/aspnet/MVCFlexigrid.aspx): public static IQueryable<T> Like<T>(this IQueryable<T> source, string propertyName, string keyword) { var type = typeof(T); var property = type.GetProperty(propertyName); var parameter = Expression.Parameter(type, "p"); var propertyAccess = Expression.MakeMemberAccess(parameter, property); var constant = Expression.Constant("%" + keyword + "%"); var like = typeof(SqlMethods).GetMethod("Like", new Type[] { typeof(string), typeof(string) }); MethodCallExpression methodExp = Expression.Call(null, like, propertyAccess, constant); Expression<Func<T, bool>> lambda = Expression.Lambda<Func<T, bool>>(methodExp, parameter); return source.Where(lambda); } With this extension method, I can simply do the following: someList.Like("FirstName", "mike"); or anotherList.Like("ProductName", "widget"); Is there an equivalent way to do this with Entity Framework? Thanks in advance.

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• Why is python decode replacing more than the invalid bytes from an encoded string?

  - by dangra

  Trying to decode an invalid encoded utf-8 html page gives different results in python, firefox and chrome. The invalid encoded fragment from test page looks like 'PREFIX\xe3\xabSUFFIX' >>> fragment = 'PREFIX\xe3\xabSUFFIX' >>> fragment.decode('utf-8', 'strict') ... UnicodeDecodeError: 'utf8' codec can't decode bytes in position 6-8: invalid data What follows is the summary of replacement policies used to handle decoding errors by python, firefox and chrome. Note how the three differs, and specially how python builtin removes the valid S (plus the invalid sequence of bytes). by Python The builtin replace error handler replaces the invalid \xe3\xab plus the S from SUFFIX by U+FFFD >>> fragment.decode('utf-8', 'replace') u'PREFIX\ufffdUFFIX' >>> print _ PREFIX?UFFIX The python implementation builtin replace error handler looks like: >>> python_replace = lambda exc: (u'\ufffd', exc.end) As expected, trying this gives same result than builtin: >>> codecs.register_error('python_replace', python_replace) >>> fragment.decode('utf-8', 'python_replace') u'PREFIX\ufffdUFFIX' >>> print _ PREFIX?UFFIX by Firefox Firefox replaces each invalid byte by U+FFFD >>> firefox_replace = lambda exc: (u'\ufffd', exc.start+1) >>> codecs.register_error('firefox_replace', firefox_replace) >>> test_string.decode('utf-8', 'firefox_replace') u'PREFIX\ufffd\ufffdSUFFIX' >>> print _ PREFIX??SUFFIX by Chrome Chrome replaces each invalid sequence of bytes by U+FFFD >>> chrome_replace = lambda exc: (u'\ufffd', exc.end-1) >>> codecs.register_error('chrome_replace', chrome_replace) >>> fragment.decode('utf-8', 'chrome_replace') u'PREFIX\ufffdSUFFIX' >>> print _ PREFIX?SUFFIX The main question is why builtin replace error handler for str.decode is removing the S from SUFFIX. Also, is there any unicode's official recommended way for handling decoding replacements?

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• Scheme - Memory System

  - by Eric

  I am trying to make a memory system where you input something in a slot of memory. So what I am doing is making an Alist and the car of the pairs is the memory location and the cdr is the val. I need the program to understand two messages, Read and Write. Read just displaying the memory location selected and the val that is assigned to that location and write changes the val of the location or address. How do I make my code so it reads the location you want it to and write to the location you want it to? Feel free to test this yourself. Any help would be much appreciated. This is what I have: (define make-memory (lambda (n) (letrec ((mem '()) (dump (display mem))) (lambda () (if (= n 0) (cons (cons n 0) mem) mem) (cons (cons (- n 1) 0) mem)) (lambda (msg loc val) (cond ((equal? msg 'read) (display (cons n val))(set! n (- n 1))) ((equal? msg 'write) (set! mem (cons val loc)) (set! n (- n 1)) (display mem))))))) (define mymem (make-memory 100))

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• Swig: No Constructor defined

  - by wheaties

  I added %allowexcept to my *.i file when building a Python <-- C++ bridge using Swig. Then I removed that preprocessing directive. Now I can't get the Python produced code to recognize the constructor of a C++ class. Here's the class file: #include <exception> class Swig_Foo{ public: Swig_Foo(){} virtual ~Swig_Foo(){} virtual getInt() =0; virtual throwException() { throw std::exception(); } }; And here's the code Swig produces from it: class Swig_Foo: __swig_setmethods__ = {} __setattr__ = lambda self, name, value: _swig_setattr(self, Swig_Foo, name, value) __swig_getmethods__ = {} __getattr__ = lambda self, name: _swig_getattr(self, Swig_Foo, name) def __init__(self): raise AttributeError, "No constructor defined" __repr__ = _swig_repr __swig_destroy__ = _foo.delete_Swig_Foo __del__ = lambda self : None; def getInt(*args): return apply(_foo.Swig_Foo_getInt, args) def throwOut(*args): return apply(_foo.Swig_Foo_throwOut, args) Swig_Foo_swigregister = _foo.Swig_Foo_swigregister Swig_Foo_swigregister(Swig_Foo) The problem is the def __init__self): raise AttributeError, "No constructor defined" portion. It never did this before I added the %allowexception and now that I've removed it, I can't get it to create a real constructor. All the other classes have actual constructors. Quite baffled. Anyone know how I can get it to stop doing this?

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• Parsing basic math equations for children's educational software?

  - by Simucal

  Inspired by a recent TED talk, I want to write a small piece of educational software. The researcher created little miniature computers in the shape of blocks called "Siftables". [David Merril, inventor - with Siftables in the background.] There were many applications he used the blocks in but my favorite was when each block was a number or basic operation symbol. You could then re-arrange the blocks of numbers or operation symbols in a line, and it would display an answer on another siftable block. So, I've decided I wanted to implemented a software version of "Math Siftables" on a limited scale as my final project for a CS course I'm taking. What is the generally accepted way for parsing and interpreting a string of math expressions, and if they are valid, perform the operation? Is this a case where I should implement a full parser/lexer? I would imagine interpreting basic math expressions would be a semi-common problem in computer science so I'm looking for the right way to approach this. For example, if my Math Siftable blocks where arranged like: [1] [+] [2] This would be a valid sequence and I would perform the necessary operation to arrive at "3". However, if the child were to drag several operation blocks together such as: [2] [\] [\] [5] It would obviously be invalid. Ultimately, I want to be able to parse and interpret any number of chains of operations with the blocks that the user can drag together. Can anyone explain to me or point me to resources for parsing basic math expressions? I'd prefer as much of a language agnostic answer as possible.

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• python VTE Terminal weirdness

  - by mykhal

  i'm trying to use the terminal from python VTE binding (python-vte from debian squeeze) as a virtual terminal emulator (just for ANSI/control chars text processing) in interactive python console, everything looks (almost) all right: >>> import vte >>> term = vte.Terminal() >>> term.feed("a\nb") >>> print repr(term.get_text(lambda *a: True).rstrip()) 'a\n b' however, launching this code (little modified) as python script, different result is yielded: $ python vte_wiredness_1.py '' strangely enough, pasting the code back into the (new) interactive python session also yields empty string: >>> import vte >>> term = vte.Terminal() >>> term.feed("a\nb") >>> print repr(term.get_text(lambda *a: True).rstrip()) '' >>> first thing caming on my mind was that the only difference between the two cases is the timing - there had to be some delay before get_text. unfortunately, preluding get_text with some seconds sleep did not help then i thought it has something to do with X window environment. but the results are the same pure linux console (with some warning on missing graphics). i wonder what causes such an unpredictable behavior (interactive console - pasted vs typed, and it's not the delay.. ant the interactive console has nothing to do with the vte terminal object.. i guess) can someone explain what is happening? is it possible to use the VTE Term such way? that the "b" letter in the output is preceded by the space, is another strangeness (all consecutive lines are preceded by more spaces.. looks like I have to send carriage return before the string.) (the lambda *a: True get_text method argument i'm using is a dummy callback, it's is some SlotSelectedCallback.. for its explanation i'd be grateful as well :) )

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• Closures in Ruby

  - by Isaac Cambron

  I'm kind of new to Ruby and some of the closure logic has me a confused. Consider this code: array = [] for i in (1..5) array << lambda {j} end array.map{|f| f.call} => [5, 5, 5, 5, 5] This makes sense to me because i is bound outside the loop, so the same variable is captured by each trip through the loop. It also makes sense to me that using an each block can fix this: array = [] (1..5).each{|i| array << lambda {i}} array.map{|f| f.call} => [1, 2, 3, 4, 5] ...because i is now being declared separately for each time through. But now I get lost: why can't I also fix it by introducing an intermediate variable? array = [] for i in 1..5 j = i array << lambda {j} end array.map{|f| f.call} => [5, 5, 5, 5, 5] Because j is new each time through the loop, I'd think a different variable would be captured on each pass. For example, this is definitely how C# works, and how -- I think-- Lisp behaves with a let. But in Ruby not so much. It almost looks like = is aliasing the variable instead of copying the reference, but that's just speculation on my part. What's really happening?

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• Alternative to using c:out to prevent XSS

  - by lynxforest

  I'm working on preventing cross site scripting (XSS) in a Java, Spring based, Web application. I have already implemented a servlet filter similar to this example http://greatwebguy.com/programming/java/simple-cross-site-scripting-xss-servlet-filter/ which sanitizes all the input into the application. As an extra security measure I would like to also sanitize all output of the application in all JSPs. I have done some research to see how this could be done and found two complementary options. One of them is the use of Spring's defaultHtmlEscape attribute. This was very easy to implement (a few lines in web.xml), and it works great when your output is going through one of spring's tags (ie: message, or form tags). The other option I have found is to not directly use EL expressions such as ${...} and instead use <c:out value="${...}" /> That second approach works perfectly, however due to the size of the application I am working on (200+ JSP files). It is a very cumbersome task to have to replace all inappropriate uses of EL expressions with the c:out tag. Also it would become a cumbersome task in the future to make sure all developers stick to this convention of using the c:out tag (not to mention, how much more unreadable the code would be). Is there alternative way to escape the output of EL expressions that would require fewer code modifications? Thank you in advance.

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