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• Why is a NullReferenceException thrown when a ToolStrip button is clicked twice with code in the `Click` event handler?

  - by Patrick

  I created a clean WindowsFormsApplication solution, added a ToolStrip to the main form, and placed one button on it. I've added also an OpenFileDialog, so that the Click event of the ToolStripButton looks like the following: private void toolStripButton1_Click(object sender, EventArgs e) { openFileDialog1.ShowDialog(); } I didn't change any other properties or events. The funny thing is that when I double-click the ToolStripButton (the second click must be quite fast, before the dialog opens), then cancel both dialogs (or choose a file, it doesn't really matter) and then click in the client area of main form, a NullReferenceException crashes the application (error details attached at the end of the post). Please note that the Click event is implemented while DoubleClick is not. What's even more strange that when the OpenFileDialog is replaced by any user-implemented form, the ToolStripButton blocks from being clicked twice. I'm using VS2008 with .NET3.5. I didn't change many options in VS (only fontsize, workspace folder and line numbering). Does anyone know how to solve this? It is 100% replicable on my machine, is it on others too? One solution that I can think of is disabling the button before calling OpenFileDialog.ShowDialog() and then enabling the button back (but it's not nice). Any other ideas? And now the promised error details: System.NullReferenceException was unhandled Message="Object reference not set to an instance of an object." Source="System.Windows.Forms" StackTrace: at System.Windows.Forms.NativeWindow.WindowClass.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) at System.Windows.Forms.UnsafeNativeMethods.PeekMessage(MSG& msg, HandleRef hwnd, Int32 msgMin, Int32 msgMax, Int32 remove) at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData) at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.Run(Form mainForm) at WindowsFormsApplication1.Program.Main() w C:\Users\Marchewek\Desktop\Workspaces\VisualStudio\WindowsFormsApplication1\Program.cs:line 20 at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args) at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() InnerException:

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• What's the difference between these LINQ queries ?

  - by SnAzBaZ

  I use LINQ-SQL as my DAL, I then have a project called DB which acts as my BLL. Various applications then access the BLL to read / write data from the SQL Database. I have these methods in my BLL for one particular table: public IEnumerable<SystemSalesTaxList> Get_SystemSalesTaxList() { return from s in db.SystemSalesTaxLists select s; } public SystemSalesTaxList Get_SystemSalesTaxList(string strSalesTaxID) { return Get_SystemSalesTaxList().Where(s => s.SalesTaxID == strSalesTaxID).FirstOrDefault(); } public SystemSalesTaxList Get_SystemSalesTaxListByZipCode(string strZipCode) { return Get_SystemSalesTaxList().Where(s => s.ZipCode == strZipCode).FirstOrDefault(); } All pretty straight forward I thought. Get_SystemSalesTaxListByZipCode is always returning a null value though, even when it has a ZIP Code that exists in that table. If I write the method like this, it returns the row I want: public SystemSalesTaxList Get_SystemSalesTaxListByZipCode(string strZipCode) { var salesTax = from s in db.SystemSalesTaxLists where s.ZipCode == strZipCode select s; return salesTax.FirstOrDefault(); } Why does the other method not return the same, as the query should be identical ? Note that, the overloaded Get_SystemSalesTaxList(string strSalesTaxID) returns a record just fine when I give it a valid SalesTaxID. Is there a more efficient way to write these "helper" type classes ? Thanks!

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• How can I strip Python logging calls without commenting them out?

  - by cdleary

  Today I was thinking about a Python project I wrote about a year back where I used logging pretty extensively. I remember having to comment out a lot of logging calls in inner-loop-like scenarios (the 90% code) because of the overhead (hotshot indicated it was one of my biggest bottlenecks). I wonder now if there's some canonical way to programmatically strip out logging calls in Python applications without commenting and uncommenting all the time. I'd think you could use inspection/recompilation or bytecode manipulation to do something like this and target only the code objects that are causing bottlenecks. This way, you could add a manipulator as a post-compilation step and use a centralized configuration file, like so: [Leave ERROR and above] my_module.SomeClass.method_with_lots_of_warn_calls [Leave WARN and above] my_module.SomeOtherClass.method_with_lots_of_info_calls [Leave INFO and above] my_module.SomeWeirdClass.method_with_lots_of_debug_calls Of course, you'd want to use it sparingly and probably with per-function granularity -- only for code objects that have shown logging to be a bottleneck. Anybody know of anything like this? Note: There are a few things that make this more difficult to do in a performant manner because of dynamic typing and late binding. For example, any calls to a method named debug may have to be wrapped with an if not isinstance(log, Logger). In any case, I'm assuming all of the minor details can be overcome, either by a gentleman's agreement or some run-time checking. :-)

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• Sharing runtime variables between files

  - by nightcracker

  I have a project with a few files that all include the header global.hpp. Those files want to share and update information that is relevant for the whole program during runtime (that data is gathered progressively during the program runs but the fields of data are known at compile-time). Now my idea was to use a struct like this: global.hpp #include <string> #ifndef _GLOBAL_SESSION_STRUCT #define _GLOBAL_SESSION_STRUCT struct session_struct { std::string username; std::string password; std::string hostname; unsigned short port; // more data fields as needed }; #endif extern struct session_struct session; main.cpp #include "global.hpp" struct session_struct session; int main(int argc, char* argv[]) { session.username = "user"; session.password = "secret"; session.hostname = "example.com"; session.port = 80; // other stuff, etc return 0; } Now every file that includes global.hpp can just read & write the fields of the session struct and easily share information. Is this the correct way to do this? NOTE: For this specific project no threading is used. But please (for future projects and other people reading) clarify in your answer how this (or your proposed) solution works when threaded. Also, for this example/project session variables are shared. But this should also apply to any other form of shared variables.

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• ASMX schema varies when using WCF Service

  - by Lijo

  Hi, I have a client (created using ASMX "Add Web Reference"). The service is WCF. The signature of the methods varies for the client and the Service. I get some unwanted parameteres to the method. Note: I have used IsRequired = true for DataMember. Service: [OperationContract] int GetInt(); Client: proxy.GetInt(out requiredResult, out resultBool); Could you please help me to make the schame non-varying in both WCF clinet and non-WCF cliet? Do we have any best practices for that? using System.ServiceModel; using System.Runtime.Serialization; namespace SimpleLibraryService { [ServiceContract(Namespace = "http://Lijo.Samples")] public interface IElementaryService { [OperationContract] int GetInt(); [OperationContract] int SecondTestInt(); } public class NameDecorator : IElementaryService { [DataMember(IsRequired=true)] int resultIntVal = 1; int firstVal = 1; public int GetInt() { return firstVal; } public int SecondTestInt() { return resultIntVal; } } } Binding = "basicHttpBinding" using NonWCFClient.WebServiceTEST; namespace NonWCFClient { class Program { static void Main(string[] args) { NonWCFClient.WebServiceTEST.NameDecorator proxy = new NameDecorator(); int requiredResult =0; bool resultBool = false; proxy.GetInt(out requiredResult, out resultBool); Console.WriteLine("GetInt___"+requiredResult.ToString() +"__" + resultBool.ToString()); int secondResult =0; bool secondBool = false; proxy.SecondTestInt(out secondResult, out secondBool); Console.WriteLine("SecondTestInt___" + secondResult.ToString() + "__" + secondBool.ToString()); Console.ReadLine(); } } } Please help.. Thanks Lijo

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• Bytecode and Objects

  - by HH

  Hey everyone, I am working on a bytecode instrumentation project. Currently when handling objects, the verifier throws an error most of the time. So I would like to get things clear concerning rules with objects (I read the JVMS but couldn't find the answer I was looking for): I am instrumenting the NEW instruction: original bytecode NEW <MyClass> DUP INVOKESPECIAL <MyClass.<init>> after instrumentation NEW <MyClass> DUP INVOKESTATIC <Profiler.handleNEW> DUP INVOKESPECIAL <MyClass.<init>> Note that I added a call to Profiler.handleNEW() which takes as argument an object reference (the newly created object). The piece of code above throws a VerificationError. While if I don't add the INVOKESTATIC (leaving only the DUP), it doesn't. So what is the rule that I'm violating? I can duplicate an uninitialized reference but I can't pass it as parameter? I would appreciate any help. Thank you

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• From where to send mails in a MVC framework, so that there is no duplication of code?

  - by Sabya

  It's a MVC question. Here is the situation: I am writing an application where I have "groups". You can invite other persons to your groups by typing their email and clicking "invite". There are two ways this functionality can be called: a) web interface and b) API After the mail sending is over I want to report to the user which mails were sent successfully (i.e., if the SMTP send succeeded. Currently, I am not interested in reporting mail bounces). So, I am thinking how should I design so that there is no code duplication. That is, API and web-interface should share the bulk of the code. To do this, I can create the method "invite" inside the model "group". So, the API and and the Web-interface can just call: group-invite($emailList); This method can send the emails. But the, problem is, then I have to access the mail templates, create the views for the mails, and then send the mails. Which should actually be in the "View" part or at least in the "Controller" part. What is the most elegant design in this situation? Note: I am really thinking to write this in the Model. My only doubt is: previously I thought sending mails also as "presentation". Since it is may be considered as a different form of generating output.

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• How Can I ReWrite flat link to a dynamic link and preserve the Query string?

  - by jeremysawesome

  Hello All, I am wanting to rewrite a url like: http://my.project/mydomain.com/ANY_NUMBER_OF_CATEGORIES/designer/4/designer-name/page.html to this: http://my.projects/mydomain.com/ANY_NUMBER_OF_CATEGORIES/page.html?designer=4 I would like to use mod-rewrite to accomplish this. Things to note: Any number of categories can be between 'mydomain.com/' and '/designer'. For instance the url could be http://my.project/mydomain.com/designer/4/designer-name/page.html or it could be http://my.project/mydomain.com/tops/shirts/small/designer/4/designer-name/page.html A query string may be provided in the original url that needs to be preserved in the rewritten url. For example url provided could be: http://my.project/mydomain.com/designer/4/designer-name/page.html?color=red&type=shirt Given the url above the resulting url would need to be: http://my.projects/mydomain.com/page.html?designer=4&color=red&type=shirt The order of the query string does not matter. The 'designer=4' part could come before or after the rest of the query string. I'm new to .htaccess and re-writes so any examples and or explanations would be greatly appreciated. Thank you very much.

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• array_map applied on a function with 2 parameters

  - by mat

  I've 2 arrays ($numbers and $letters) and I want to create a new array based on a function that combines every $numbers with every $letters. The parameters of this function involes the value of both $numbers and $letters. (Note: $numbers and $letters doesn't have the same amount of values). I need something like this: $numbers = array(1,2,3,4,5,6,...); $letters = array('a','b','c','d','e',...); function myFunction($x,$y){ // $output = some code that use $x and $y return $output; }; $array_1 = array( (myFunction($numbers[0],$letters[0])), (myFunction($numbers[0],$letters[1])), myFunction($numbers[0],$letters[2]), myFunction($numbers[0],$letters[3]), etc); $array_2 = array( (myFunction($numbers[1],$letters[0])), (myFunction($numbers[1],$letters[1])), myFunction($numbers[1],$letters[2]), myFunction($numbers[1],$letters[3]), etc); $array_3 = array( (myFunction($numbers[2],$letters[0])), (myFunction($numbers[2],$letters[1])), myFunction($numbers[2],$letters[2]), myFunction($numbers[2],$letters[3]), etc); ... $array_N = array( (myFunction($numbers[N],$letters[0])), (myFunction($numbers[N],$letters[1])), myFunction($numbers[N],$letters[2]), myFunction($numbers[N],$letters[3]), etc); $array = array($array_1, $array_2, $array_3, etc.); I know that this may work, but it's a lot of code, especially if I have a many values for each array. Is there a way to get the same result with less code? I tried this, but it's not working: $array = array_map("myFunction($value, $letters)",$numbers)); Any help would be appriciated!

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• Point data structure for a sketching application

  - by bebraw

  I am currently developing a little sketching application based on HTML5 Canvas element. There is one particular problem I haven't yet managed to find a proper solution for. The idea is that the user will be able to manipulate existing stroke data (points) quite freely. This includes pushing point data around (ie. magnet tool) and manipulating it at whim otherwise (ie. altering color). Note that the current brush engine is able to shade by taking existing stroke data in count. It's a quick and dirty solution as it just iterates the points in the current stroke and checks them against a distance rule. Now the problem is how to do this in a nice manner. It is extremely important to be able to perform efficient queries that return all points within given canvas coordinate and radius. Other features, such as space usage, should be secondary to this. I don't mind doing some extra processing between strokes while the user is not painting. Any pointers are welcome. :)

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• Android depth buffer issue: Advice for anyone experiencing problem

  - by Andrew Smith

  I've wasted around 30 hours this week writing and re-writing code, believing that I had misunderstood how the OpenGL depth buffer works. Everything I tried, failed. I have now resolved my problem by finding what may be an error in the Android implementation of OpenGL. See this API entry: http://www.opengl.org/sdk/docs/man/xhtml/glClearDepth.xml void glClearDepth(GLclampd depth); Specifies the depth value used when the depth buffer is cleared. The initial value is 1. Android's implementation has two versions of this command: glClearDepthx which takes an integer value, clamped 0-1 glClearDepthf which takes a floating point value, clamped 0-1 If you use glClearDepthf(1) then you get the results you would expect. If you use glClearDepthx(1), as I was doing then you get different results. (Note that 1 is the default value, but calling the command with the argument 1 produces different results than not calling it at all.) Quite what is happening I do not know, but the depth buffer was being cleared to a value different from what I had specified.

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• -(void)dealloc - How ? Objective - C

  - by sagar

  Please Note that - this is not similar than this question. OK. To understand my question, First of all please see both of these destructors. - (void)dealloc { [Marketdetails release]; Marketdetails=nil; [parsedarray release]; parsedarray=nil; [Marketid release]; Marketid=nil; [marketname release]; marketname=nil; [super dealloc]; } - (void)dealloc { [super dealloc]; [Marketdetails release]; Marketdetails=nil; [parsedarray release]; parsedarray=nil; [Marketid release]; Marketid=nil; [marketname release]; marketname=nil; } See, Both destructors have different code. In First Destructor first current class objects are released & then [super dealloc] is called. In second Desctructor first [super dealloc] is called. My question is as follows. Where should we write [super dealloc] ? first or last ? or it doesn't matter ?

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• How can I get the main thread to sleep while waiting for a delgate to be called?

  - by Erik B

  Consider a class with these methods: - (id) initWithFrame: (CGRect) frame { if (!(self = [super init])) return nil; webView = [[UIWebView alloc] initWithFrame:frame]; [webView setDelegate:self]; lock = [[NSConditionLock alloc] initWithCondition:LOCK_WAIT]; return self; } - (void) setHTML: (NSString *) html { [lock lockWhenCondition:LOCK_WAIT]; [webView loadHTMLString:html baseURL:nil]; [lock unlock]; } - (void)webViewDidFinishLoad:(UIWebView *)aWebView { [lock lockWhenCondition:LOCK_WAIT]; // Locking to be able to unlock and change the condition. [lock unlockWithCondition:LOCK_GO]; } - (NSString *) stringByEvaluatingJavaScriptFromString: (NSString *) jsCommand { [lock lockWhenCondition:LOCK_GO]; return [webView stringByEvaluatingJavaScriptFromString:jsCommand]; [lock unlock]; } Let's call this class SynchronousUIWebView. From the main thread I execute: webView = [[SynchronousUIWebView alloc] initWithFrame:frame]; [webView setHTML:html]; [webView stringByEvaluatingJavaScriptFromString:jsCommand]; The problem seems to be that the delegate is not called until I leave the current call stack, which I don't since I'm waiting for the delegate call to happen, aka deadlock. To me it seems like the delegate call is pushed to a queue that is called when the current call is done. So the question is can I modify this behavior? Note: The reason this is needed is that I can't execute the JavaScript until the HTML has loaded.

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• Cant print contents of a custom file

  - by ZaZu

  Hello, Im trying to scan contents from a random file into an array in a structure. Then I want to print those contents on screen. (NOTE: The following code is from a bigger program, this is just a sample, but all structures and arrays used are needed as declared ) The contents of the file being tested are simply: 5 4 3 2 5 3 4 2 #include<stdio.h> #define first 500 #define sec 500 struct trial{ int f; int r; float what[first][sec]; }; int trialtest(trial *test); int trialdisplay(trial *test); main(){ trial test; trialtest(&test); trialdisplay(&test); } int trialtest(trial *test){ int z,x,i; FILE *inputf; inputf=fopen("randomfile.txt","r"); for(i=0;i<5;i++){ fscanf(inputf,"%f",&(*test).what[z][x]); } fclose(inputf); return 0; } int trialdisplay(trial *test){ int i,z,x; printf("printing\n\n\n"); for (i=0;i<10;i++){ printf("%f",(*test).what[z][x]); } return 0; } The problem is, I get this error whenever I run the code .. I cant really understand whats going on : Any suggestions ? Thanks alot !

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• Ruby : UTF-8 IO

  - by subtenante

  I use ruby 1.8.7. I try to parse some text files containing greek sentences, encoded in UTF-8. (I can't much paste here sample files, because they are subject to copyright. Really just some greek text encoded in UTF-8.) I want, for each file, to parse the file, extract all the words, and make a list of each new word found in this file. All that saved to one big index file. Here is my code : #!/usr/bin/ruby -KU def prepare_line(l) l.gsub(/^\s*[ST]\d+\s*:\s*|\s+$|\(\d+\)\s*/u, "") end def tokenize(l) l.split /['·.;!:\s]+/u end $dict = {} $cpt = 0 $out = File.new 'out.txt', 'w' def lesson(file) $cpt = $cpt + 1 file.readlines.each do |l| $out.puts l l = prepare_line l tokenize(l).each do |t| unless $dict[t] $dict[t] = $cpt $out.puts " #{t}\n" end end end end Dir.new('etc/').each do |filename| f = File.new("etc/#{filename}") unless File.directory? f lesson f end end Here is part of my output : ?@???†?†?????????? ?...[snip very long hangul/hanzi mishmash]... ????????†? ???N2 : ?e?te?? (2) µ???µa (Note that the puts l part seems to work fine, at the end of the given output line.) Any idea what is wrong with my code ? (General comments about ruby idioms I could use are very welcome, I'm really a beginner.)

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• How to efficiently convert String, integer, double, datetime to binary and vica versa?

  - by Ben

  Hi, I'm quite new to C# (I'm using .NET 4.0) so please bear with me. I need to save some object properties (their properties are int, double, String, boolean, datetime) to a file. But I want to encrypt the files using my own encryption, so I can't use FileStream to convert to binary. Also I don't want to use object serialization, because of performance issues. The idea is simple, first I need to somehow convert objects (their properties) to binary (array), then encrypt (some sort of xor) the array and append it to the end of the file. When reading first decrypt the array and then somehow convert the binary array back to object properties (from which I'll generate objects). I know (roughly =) ) how to convert these things by hand and I could code it, but it would be useless (too slow). I think the best way would be just to get properties' representation in memory and save that. But I don't know how to do it using C# (maybe using pointers?). Also I though about using MemoryStream but again I think it would be inefficient. I am thinking about class Converter, but it does not support toByte(datetime) (documentation says it always throws exception). For converting back I think the only options is class Converter. Note: I know the structure of objects and they will not change, also the maximum String length is also known. Thank you for all your ideas and time. EDIT: I will be storing only parts of objects, in some cases also parts of different objects (a couple of properties from one object type and a couple from another), thus I think that serialization is not an option for me.

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• Managing multiple customer databases in ASP.NET MVC application

  - by Robert Harvey

  I am building an application that requires separate SQL Server databases for each customer. To achieve this, I need to be able to create a new customer folder, put a copy of a prototype database in the folder, change the name of the database, and attach it as a new "database instance" to SQL Server. The prototype database contains all of the required table, field and index definitions, but no data records. I will be using SMO to manage attaching, detaching and renaming the databases. In the process of creating the prototype database, I tried attaching a copy of the database (companion .MDF, .LDF pair) to SQL Server, using Sql Server Management Studio, and discovered that SSMS expects the database to reside in c:\program files\Microsoft SQL Server\MSSQL.1\MSSQL\DATA\MyDatabaseName.MDF Is this a "feature" of SQL Server? Is there a way to manage individual databases in separate directories? Or am I going to have to put all of the customer databases in the same directory? (I was hoping for a little better control than this). NOTE: I am currently using SQL Server Express, but for testing purposes only. The production database will be SQL Server 2008, Enterprise version. So "User Instances" are not an option.

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• Tools\addin's for formating or cleaning up xaml?

  - by cody

  I'm guessing these don't exist since I searched around for these but I'm looking for a few tools: 1) A tool that cleans up my xaml so that the properties of elements are consistent through a file. I think enforcing that consistence would make the xaml easier to read. Maybe there could be a hierarchy of what comes first but if not alphabetical might work. Example before: TextBox Name="myTextBox1" Grid.Row="3" Grid.Column="1" Margin="4" TextBox Grid.Column="1" Margin="4" Name="t2" Grid.Row="3" Example after: TextBox Name="myTextBox1" Grid.Row="3" Grid.Column="1" Margin="4" TextBox Name="t2" Grid.Row="3" Grid.Column="1" Margin="4" (note < / has been remove from the above since control seem to have issues parsing whe the after section was added) 2) Along the same lines as above, to increase readability, a tool to align properties, so from the above code example similar props would start in the same place. <TextBox Name="myTextBox1" Grid.Row="3" Grid.Column="1" Margin="4"/> <TextBox Name="t2" Grid.Row="3" Grid.Column="1" Margin="4"/> I know VS has default settings for XAML documents so props can be on one line or separate lines so maybe if there was a tool as described in (1) this would not be needed...but it would still be nice if you like your props all on one line. 3) A tool that adds X to the any of the Grid.Row values and Y to any of the Grid.Column values in the selected text. Every time I add a new row\column I have to go manually fix these. From my understanding Expression Blend can help with this but seem excessive to open Blend just to increment some numbers (and just don't grok Blend). Maybe vs2010 with the designer will help but right now I'm on VS08 and Silverlight. Any one know of any tools to help with this? Anyone planning to write something like this...I'm looking at you JetBrains and\or DevExpress. Thanks.

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• Creating a simple command line interface (CLI) using a python server (TCP sock) and few scripts

  - by VN44CA

  I have a Linux box and I want to be able to telnet into it (port 77557) and run few required commands without having to access to the whole Linux box. So, I have a server listening on that port, and echos the entered command on the screen. (for now) Telnet 192.168.1.100 77557 Trying 192.168.1.100... Connected to 192.168.1.100. Escape character is '^]'. hello<br /> You typed: "hello"<br /> NOW: I want to create lot of commands that each take some args and have error codes. Anyone has done this before? It would be great if I can have the server upon initialization go through each directory and execute the init.py file and in turn, the init.py file of each command call into a main template lib API (e.g. RegisterMe()) and register themselves with the server as function call backs. At least this is how I would do it in C/C++. But I want the best Pythonic way of doing this. /cmd/ /cmd/myreboot/ /cmd/myreboot/ini.py (note underscore don't show for some reason) /cmd/mylist/ /cmd/mylist/init.py ... etc IN: /cmd/myreboot/_ini_.py: from myMainCommand import RegisterMe RegisterMe(name="reboot",args=Arglist, usage="Use this to reboot the box", desc="blabla") So, repeating this creates a list of commands and when you enter the command in the telnet session, then the server goes through the list, matches the command and passed the args to that command and the command does the job and print the success or failure to stdout. Thx

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• Pairs from single list

  - by Apalala

  Often enough, I've found the need to process a list by pairs. I was wondering which would be the pythonic and efficient way to do it, and found this on Google: pairs = zip(t[::2], t[1::2]) I thought that was pythonic enough, but after a recent discussion involving idioms versus efficiency, I decided to do some tests: import time from itertools import islice, izip def pairs_1(t): return zip(t[::2], t[1::2]) def pairs_2(t): return izip(t[::2], t[1::2]) def pairs_3(t): return izip(islice(t,None,None,2), islice(t,1,None,2)) A = range(10000) B = xrange(len(A)) def pairs_4(t): # ignore value of t! t = B return izip(islice(t,None,None,2), islice(t,1,None,2)) for f in pairs_1, pairs_2, pairs_3, pairs_4: # time the pairing s = time.time() for i in range(1000): p = f(A) t1 = time.time() - s # time using the pairs s = time.time() for i in range(1000): p = f(A) for a, b in p: pass t2 = time.time() - s print t1, t2, t2-t1 These were the results on my computer: 1.48668909073 2.63187503815 1.14518594742 0.105381965637 1.35109519958 1.24571323395 0.00257992744446 1.46182489395 1.45924496651 0.00251388549805 1.70076990128 1.69825601578 If I'm interpreting them correctly, that should mean that the implementation of lists, list indexing, and list slicing in Python is very efficient. It's a result both comforting and unexpected. Is there another, "better" way of traversing a list in pairs? Note that if the list has an odd number of elements then the last one will not be in any of the pairs. Which would be the right way to ensure that all elements are included? I added these two suggestions from the answers to the tests: def pairwise(t): it = iter(t) return izip(it, it) def chunkwise(t, size=2): it = iter(t) return izip(*[it]*size) These are the results: 0.00159502029419 1.25745987892 1.25586485863 0.00222492218018 1.23795199394 1.23572707176 Results so far Most pythonic and very efficient: pairs = izip(t[::2], t[1::2]) Most efficient and very pythonic: pairs = izip(*[iter(t)]*2) It took me a moment to grok that the first answer uses two iterators while the second uses a single one. To deal with sequences with an odd number of elements, the suggestion has been to augment the original sequence adding one element (None) that gets paired with the previous last element, something that can be achieved with itertools.izip_longest().

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• Hierarchy of meaning

  - by asldkncvas

  I am looking for a method to build a hierarchy of words. Background: I am a "amateur" natural language processing enthusiast and right now one of the problems that I am interested in is determining the hierarchy of word semantics from a group of words. For example, if I have the set which contains a "super" representation of others, i.e. [cat, dog, monkey, animal, bird, ... ] I am interested to use any technique which would allow me to extract the word 'animal' which has the most meaningful and accurate representation of the other words inside this set. Note: they are NOT the same in meaning. cat != dog != monkey != animal BUT cat is a subset of animal and dog is a subset of animal. I know by now a lot of you will be telling me to use wordnet. Well, I will try to but I am actually interested in doing a very domain specific area which WordNet doesn't apply because: 1) Most words are not found in Wordnet 2) All the words are in another language; translation is possible but is to limited effect. another example would be: [ noise reduction, focal length, flash, functionality, .. ] so functionality includes everything in this set. I have also tried crawling wikipedia pages and applying some techniques on td-idf etc but wikipedia pages doesn't really do much either. Can someone possibly enlighten me as to what direction my research should go towards? (I could use anything)

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• How to Perform Continues Iteration over Shared Dictionary in Multi-threaded Environment

  - by Mubashar Ahmad

  Dear Gurus. Note Pls do not tell me regarding alternative to custom session, Pls answer only relative to the Pattern Scenario I have Done Custom Session Management in my application(WCF Service) for this I have a Dictionary shared to all thread. When a specific function Gets called I add a New Session and Issue SessionId to the client so it can use that sessionId for rest of his calls until it calls another specific function, which terminates this session and removes the session from the Dictionary. Due to any reason Client may not call session terminator function so i have to implement time expiration logic so that i can remove all such sessions from the memory. For this I added a Timer Object which calls ClearExpiredSessions function after the specific period of time. which iterates on the dictionary. Problem: As this dictionary gets modified every time new client comes and leaves so i can't lock the whole dictionary while iterating over it. And if i do not lock the dictionary while iteration, if dictionary gets modified from other thread while iterating, Enumerator will throw exception on MoveNext(). So can anybody tell me what kind of Design i should follow in this case. Is there any standard pattern available.

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• std::string insert method has ambiguous overloads?

  - by sdg

  Environment: VS2005 C++ using STLPort 5.1.4. Compiling the following code snippet: std::string copied = "asdf"; char ch = 's'; copied.insert(0,1,ch); I receive an error: Error 1 error C2668: 'stlpx_std::basic_string<_CharT,_Traits,_Alloc>::insert' : ambiguous call to overloaded function It appears that the problem is the insert method call on the string object. The two defined overloads are void insert ( iterator p, size_t n, char c ); string& insert ( size_t pos1, size_t n, char c ); But given that STLPort uses a simple char* as its iterator, the literal zero in the insert method in my code is ambiguous. So while I can easily overcome the problem by hinting such as copied.insert(size_t(0),1,ch); My question is: is this overloading and possible ambiguity intentional in the specification? Or more likely an unintended side-effect of the specific STLPort implementation? (Note that the Microsoft-supplied STL does not have this problem as it has a class for the iterator, instead of a naked pointer)

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• floating point equality in Python and in general

  - by eric.frederich

  I have a piece of code that behaves differently depending on whether I go through a dictionary to get conversion factors or whether I use them directly. The following piece of code will print 1.0 == 1.0 -> False But if you replace factors[units_from] with 10.0 and factors[units_to ] with 1.0 / 2.54 it will print 1.0 == 1.0 -> True #!/usr/bin/env python base = 'cm' factors = { 'cm' : 1.0, 'mm' : 10.0, 'm' : 0.01, 'km' : 1.0e-5, 'in' : 1.0 / 2.54, 'ft' : 1.0 / 2.54 / 12.0, 'yd' : 1.0 / 2.54 / 12.0 / 3.0, 'mile' : 1.0 / 2.54 / 12.0 / 5280, 'lightyear' : 1.0 / 2.54 / 12.0 / 5280 / 5.87849981e12, } # convert 25.4 mm to inches val = 25.4 units_from = 'mm' units_to = 'in' base_value = val / factors[units_from] ret = base_value * factors[units_to ] print ret, '==', 1.0, '->', ret == 1.0 Let me first say that I am pretty sure what is going on here. I have seen it before in C, just never in Python but since Python in implemented in C we're seeing it. I know that floating point numbers will change values going from a CPU register to cache and back. I know that comparing what should be two equal variables will return false if one of them was paged out while the other stayed resident in a register. Questions What is the best way to avoid problems like this?... In Python or in general. Am I doing something completely wrong? Side Note This is obviously part of a stripped down example but what I'm trying to do is come with with classes of length, volume, etc that can compare against other objects of the same class but with different units. Rhetorical Questions If this is a potentially dangerous problem since it makes programs behave in an undetermanistic matter, should compilers warn or error when they detect that you're checking equality of floats Should compilers support an option to replace all float equality checks with a 'close enough' function? Do compilers already do this and I just can't find the information.

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• Packet fragmentation when sending data via SSLStream

  - by Ive

  When using an SSLStream to send a 'large' chunk of data (1 meg) to a (already authenticated) client, the packet fragmentation / dissasembly I'm seeing is FAR greater than when using a normal NetworkStream. Using an async read on the client (i.e. BeginRead()), the ReadCallback is repeatedly called with exactly the same size chunk of data up until the final packet (the remainder of the data). With the data I'm sending (it's a zip file), the segments happen to be 16363 bytes long. Note: My receive buffer is much bigger than this and changing it's size has no effect I understand that SSL encrypts data in chunks no bigger than 18Kb, but since SSL sits on top of TCP, I wouldn't think that the number of SSL chunks would have any relevance to the TCP packet fragmentation? Essentially, the data is taking about 20 times longer to be fully read by the client than with a standard NetworkStream (both on localhost!) What am I missing? EDIT: I'm beginning to suspect that the receive (or send) buffer size of an SSLStream is limited. Even if I use synchronous reads (i.e. SSLStream.Read()), no more data ever becomes available, regardless of how long I wait before attempting to read. This would be the same behavior as if I were to limit the receive buffer to 16363 bytes. Setting the Underlying NetworkStream's SendBufferSize (on the server), and ReceiveBufferSize (on the client) has no effect.

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