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  • What are the common programming mistakes in Python?

    - by Paul McGuire
    I was about to tag the recent question in which the OP accidentally shadowed the builtin operator module with his own local operator.py with the "common-mistakes" tag, and I saw that there are a number of interesting questions posted asking for common mistakes to avoid in Java, Ruby, Scala, Clojure, .Net, jQuery, Haskell, SQL, ColdFusion, and so on, but I didn't see any for Python. For the benefit of Python beginners, can we enumerate the common mistakes that we have all committed at one time or another, in the hopes of maybe steering a newbie or two clear of them? (In homage to "The Princess Bride", I call these the Classic Blunders.) If possible, a little supporting explanation on what the problem is, and the generally accepted resolution/workaround, so that the beginning Pythoner doesn't read your answer and say "ok, that's a mistake, how do I fix it?"

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  • ASP.NET MVC null ViewResult

    - by David Neale
    How should one deal with an MVC controller returning a null ViewResult? As an example I am creating a simple edit view: public ActionResult Edit(int id) { var person = (from p in context.SWLiftShare_Persons where p.id == id select p).SingleOrDefault(); if (person != null) { return View(person); } else return View(); } I guess in reality there's no point in checking for a null result in the controller because the view picks out properties from the model: <h2>Edit - <%= Html.Encode(Model.Name) %></h2> <%= Html.ValidationSummary("Edit was unsuccessful. Please correct the errors and try again.") %> <% using (Html.BeginForm()) {%> <fieldset> <legend>Fields</legend> <p> <label for="id">id: <%= Html.Encode(Model.id) %></label> </p> <p> <label for="CollarNumber">CollarNumber:</label> <%= Html.TextBox("CollarNumber", Model.CollarNumber)%> <%= Html.ValidationMessage("CollarNumber", "*") %> </p> <p> <label for="Name">Name:</label> <%= Html.TextBox("Name", Model.Name)%> <%= Html.ValidationMessage("Name", "*") %> </p> <p> <label for="EmailAddress">EmailAddress:</label> <%= Html.TextBox("EmailAddress", Model.EmailAddress, new { style = "width:300px" })%> <%= Html.ValidationMessage("EmailAddress", "*") %> </p> <p> <input type="submit" value="Save" /> </p> </fieldset> <% } %> I could just wrap everything in a <% if(Model != null) { //render edit markup... etc. but that seems rather unelegant. Is there a better way to deal with this?

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  • Rounded Corners Image Change on Hover

    - by Sarfraz
    Hello, I created a rounded box/button and sliced its first corner, the middle bar (which repeats horizontally to adjust the width of the button text/content) and the last corner and used following markup: <div id="left-corner"></div> <div id="middle-bar">About Us</div> <div id="right-corner"></div> These divs have corresponding images from CSS and are floated left. Those three divs create a single rounded button wiht text About Us which is fine. Problem: I have also created similar three slices of hover images but I wonder how to apply hover to those buttons because if I use :hover with these hovered slices, then even hovering on corner images also creates hovering effect. One alternative is to use fixed width buttons and slice buttons completely but I do not want to do that.

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  • What should be the "trunk" development, or release

    - by Nix
    I have the unfortunate opportunity of source control via Borland's StarTeam. It unfortunately does very few things well, and one supreme weakness is its view management. I love SVN and come from an SVN mindset. Our issue is post production release we are spending countless hours merging changes into a "production support" environment. Please do not harass me this was not my doing, I inherited it and am trying to present a better way of managing the repository. It is not an option to switch to a different SCM tool. Current setup Product.1.0 (TRUNK, current production code, and at this level are pending bug fixes) Product.2.0(true trunk anything checked in gets tested, and then released next production cycle, a lot of changes occur in this view) My proposal is going to be to swap them, have all development be done on the trunk (Production), tag on releases, and as needed create child views to represent production support bug fixes. Production Production.2.0.SP.1 I can not find any documentation to support the above proposal so I am trying to get feedback on whether or not the change is a good idea and if there is anything you would recommend doing differently.

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  • Is there a way to generate a short random id, avoiding collisions, without hitting persistent storag

    - by bshacklett
    If you've used GoToMeeting, that's the type of ID I want. I'd like it to be random so that it obfuscates the number of items being tracked and short, so that it's easy to reference manually; UUIDs are way too long. I'd like to avoid hitting persistent storage merely for performance reasons, but I can't think of any other way to avoid collisions. Is 9 digits enough to do something time-based?

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  • Spring online repository for Maven

    - by Fortyrunner
    I've just installed Maven2 for the first time. By default it pulls down a few useful jars into a local project: jakarta-commons, junit etc. I wanted to pull in the latest Spring release (2.5.6 at the time of writing). But the online repositories I looked at (iBiblio and Maven) only had much older versions of Spring libraries. Are there any other repositories that are kept up to date? What is the best practice here; can we maintain them ourselves? I would be prepared to help out maintaining this stuff!

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  • Best practice for handling ConnectionDroppedHandler in OCS Server Application

    - by Paul Nearney
    Hi all, In general, it seems that the majority of times that ConnectionDroppedHandler would get called in an OCS server application is for expected reasons e.g. server application has been unregistered, server is shutting down, etc. Are there any unexpected situations in which ConnectionDroppedHandler can be called? Basically, i'm wondering whether it will ever be necessary to log an error to the event log from this event handler. Many thanks, Paul

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  • Is it better to use List or Collection?

    - by Vivin Paliath
    I have an object that stores some data in a list. The implementation could change later, and I don't want to expose the internal implementation to the end user. However, the user must have the ability to modify and access this collection of data. Currently I have something like this: public List<SomeDataType> getData() { return this.data; } public void setData(List<SomeDataType> data) { this.data = data; } Does this mean that I have allowed the internal implementation details to leak out? Should I be doing this instead? public Collection<SomeDataType> getData() { return this.data; } public void setData(Collection<SomeDataType> data) { this.data = new ArrayList<SomeDataType>(data); }

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  • Is there any reason for an object pool to not be treated as a singleton?

    - by Chris Charabaruk
    I don't necessarily mean implemented using the singleton pattern, but rather, only having and using one instance of a pool. I don't like the idea of having just one pool (or one per pooled type). However, I can't really come up with any concrete situations where there's an advantage to multiple pools for mutable types, at least not any where a single pool can function just as well. What advantages are there to having multiple pools over a singleton pool?

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  • When is JavaScript's eval() not evil?

    - by Richard Turner
    I'm writing some JavaScript to parse user-entered functions (for spreadsheet-like functionality). Having parsed the formula I could convert it into JavaScript and run eval() on it to yield the result. However, I've always shied away from using eval() if I can avoid it because it's evil (and, rightly or wrongly, I've always thought it is even more evil in JavaScript because the code to be evaluated might be changed by the user). Obviously one has to use eval() to parse JSON (I presume that JS libraries use eval() for this somewhere, even if they run the JSON through a regex check first), but when else, other than when manipulating JSON, it is OK to use eval()?

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  • How to handle multiple delegates

    - by mac_55
    I've got a view in my app that does pretty much everything, and I like it that way. The problem however is that it's implementing 5 or 6 different delegates, which seems a little bit messy. My question is, does the view controller have to implement all of the delegates? or is there some way I can separate the code out into different files (without having to do a major restructure or rewrite)? Here's all the delegates I'm implementing: @interface MyView : UIViewController <UIScrollViewDelegate, UIImagePickerControllerDelegate, UINavigationControllerDelegate, UIActionSheetDelegate, MFMailComposeViewControllerDelegate>

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  • Decorator pattern in C++

    - by AlgoMan
    Can someone give me an example of Decorator pattern in C++ ? I have come across the Java version of it. But C++ i have found it difficult to understand the examples that are given.

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  • How do I delete a file from depot, but leave local copy in tact?

    - by Gary
    I'm trying to learn Perforce and want to delete a file from the depot(easy to do with p4 delete, p4 submit), but that deletes it from the client machine dir structure as well. I want to keep my local file in my directory intact. The only way I can see to do this would be to move it out of the hierarchy that is under Perforce control before deleting. I was able to get my file back by syncing an earlier version. Maybe I set up my client workspace wrong? Or am I misunderstanding a fundamental concept of source control? The client workspace is /home/user and I did it this way so I could add any file under my home directory without getting an error about the file not being under client's root. FYI - Linux client and server running P4D/LINUX26X86/2009.1/222893 (2009/11/12) Any advice appreciated. Thanks.

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  • ASP.NET MVC Paging for a search form

    - by James Alexander
    I've read several different posts on paging w/ in MVC but none describe a scenario where I have something like a search form and then want to display the results of the search criteria (with paging) beneath the form once the user clicks submit. My problem is that, the paging solution I'm using will create <a href="..."> links that will pass the desired page like so: http://mysite.com/search/2/ and while that's all fine and dandy, I don't have the results of the query being sent to the db in memory or anything so I need to query the DB again. If the results are handled by the POST controller action for /Search and the first page of the data is rendered as such, how do I get the same results (based on the form criteria specified by the user) when the user clicks to move to page 2? Some javascript voodoo? Leverage Session State? Make my GET controller action have the same variables expected by the search criteria (but optional), when the GET action is called, instantiate a FormCollection instance, populate it and pass it to the POST action method (there-by satisfying DRY)? Can someone point me in the right direction for this scenario or provide examples that have been implemented in the past? Thanks!

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  • Drupal: Content in blocks from node_reference fields?

    - by Marco
    After only a few weeks of working with Drupal I've come up with a recurring problem, which I don't really have an optimal solution to, so I'm hoping that someone here might be able to give some best practice pointers. What I have is a region inside my node.tpl.php, which is populated with blocks that display content from two different CCK fields of the type node_reference. This works fine when displaying a single node. The problem appears when I need to use a view. For example, lets say I have a news listing, and a single news item view. When I display the single news item I can use the news node node_reference field to reference whatever material I would like to have in my sidebar, but when on the news listing view I would like to reference nodes separately. What would be the best practice to solve this? I'm having a few ideas, but none seem like the logical choice, how would you do?

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  • Best Practice With JFrame Constructors?

    - by David Barry
    In both my Java classes, and the books we used in them laying out a GUI with code heavily involved the constructor of the JFrame. The standard technique in the books seems to be to initialize all components and add them to the JFrame in the constructor, and add anonymous event handlers to handle events where needed, and this is what has been advocated in my class. This seems to be pretty easy to understand, and easy to work with when creating a very simple GUI, but seems to quickly get ugly and cumbersome when making anything other than a very simple gui. Here is a small code sample of what I'm describing: public class FooFrame extends JFrame { JLabel inputLabel; JTextField inputField; JButton fooBtn; JPanel fooPanel; public FooFrame() { super("Foo"); fooPanel = new JPanel(); fooPanel.setLayout(new FlowLayout()); inputLabel = new JLabel("Input stuff"); fooPanel.add(inputLabel); inputField = new JTextField(20); fooPanel.add(inputField); fooBtn = new JButton("Do Foo"); fooBtn.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { //handle event } }); fooPanel.add(fooBtn); add(fooPanel, BorderLayout.CENTER); } } Is this type of use of the constructor the best way to code a Swing application in java? If so, what techniques can I use to make sure this type of constructor is organized and maintainable? If not, what is the recommended way to approach putting together a JFrame in java?

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  • Passing data structures to different threads

    - by Robb
    I have an application that will be spawning multiple threads. However, I feel there might be an issue with threads accessing data that they shouldn't be. I'm relatively new to threading so bare with me. Here is the structure of the threaded application (sorry for the crudeness): MainThread / \ / \ / \ Thread A Thread B / \ / \ / \ / \ / \ / \ Thread A_1 Thread A_2 Thread B_1 Thread B_2 Under each lettered thread (which could be many), there will only be two threads and they are fired of sequentially. The issue i'm having is I'm not entirely sure how to pass in a datastructure into these threads. So, the datastructure is created in MainThread, will be modified in the lettered thread (Thread A, etc) specific to that thread and then a member variable from that datastructure is sent to Letter_Numbered threads. Currently, the lettered thread class has a member variable and when the class is constructed, the datastructure from mainthread is passed in by reference, invoking the copy constructor so the lettered thread has it's own copy to play with. The lettered_numbered thread simply takes in a string variable from the data structure within the lettered thread. My question is, is this accceptable? Is there a much better way to ensure each lettered thread gets its own data structure to play with? Sorry for the somewhat poor explanation, please leave comments and i'll try to clarify.

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  • Disposing underlying object from finalizer in an immutable object

    - by Juan Luis Soldi
    I'm trying to wrap around Awesomium and make it look to the rest of my code as close as possible to NET's WebBrowser since this is for an existing application that already uses the WebBrowser. In this library, there is a class called JSObject which represents a javascript object. You can get one of this, for instance, by calling the ExecuteJavascriptWithResult method of the WebView class. If you'd call it like myWebView.ExecuteJavascriptWithResult("document", string.Empty).ToObject(), then you'd get a JSObject that represents the document. I'm writing an immutable class (it's only field is a readonly JSObject object) called JSObjectWrap that wraps around JSObject which I want to use as base class for other classes that would emulate .NET classes such as HtmlElement and HtmlDocument. Now, these classes don't implement Dispose, but JSObject does. What I first thought was to call the underlying JSObject's Dispose method in my JSObjectWrap's finalizer (instead of having JSObjectWrap implement Dispose) so that the rest of my code can stay the way it is (instead of having to add using's everywhere and make sure every JSObjectWrap is being properly disposed). But I just realized if more than two JSObjectWrap's have the same underlying JSObject and one of them gets finalized this will mess up the other JSObjectWrap. So now I'm thinking maybe I should keep a static Dictionary of JSObjects and keep count of how many of each of them are being referenced by a JSObjectWrap but this sounds messy and I think could cause major performance issues. Since this sounds to me like a common pattern I wonder if anyone else has a better idea.

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  • How can i return abstract class from any factory?

    - by programmerist
    using System; using System.Collections.Generic; using System.Linq; using System.Web; namespace EfTestFactory { public abstract class _Company { public abstract List<Personel> GetPersonel(); public abstract List<Prim> GetPrim(); public abstract List<Finans> GetFinans(); } public abstract class _Radyoloji { public abstract List<string> GetRadyoloji(); } public abstract class _Satis { public abstract List<string> GetSatis(); } public abstract class _Muayene { public abstract List<string> GetMuayene(); } public class Company : _Company { public override List<Personel> GetPersonel() { throw new NotImplementedException(); } public override List<Prim> GetPrim() { throw new NotImplementedException(); } public override List<Finans> GetFinans() { throw new NotImplementedException(); } } public class Radyoloji : _Radyoloji { public override List<string> GetRadyoloji() { throw new NotImplementedException(); } } public class Satis : _Satis { public override List<string> GetSatis() { throw new NotImplementedException(); } } public class Muayene : _Muayene { public override List<string> GetMuayene() { throw new NotImplementedException(); } } public class GenoTipController { public object CreateByEnum(DataModelType modeltype) { string enumText = modeltype.ToString(); // will return for example "Company" Type classType = Type.GetType(enumText); // the Type for Company class object t = Activator.CreateInstance(classType); // create an instance of Company class return t; } } public class AntsController { static Dictionary<DataModelType, Func<object>> s_creators = new Dictionary<DataModelType, Func<object>>() { { DataModelType.Radyoloji, () => new _Radyoloji() }, { DataModelType.Company, () => new _Company() }, { DataModelType.Muayene, () => new _Muayene() }, { DataModelType.Satis, () => new _Satis() }, }; public object CreateByEnum(DataModelType modeltype) { return s_creators[modeltype](); } } public class CompanyView { public static List<Personel> GetPersonel() { GenoTipController controller = new GenoTipController(); _Company company = controller.CreateByEnum(DataModelType.Company) as _Company; return company.GetPersonel(); } } public enum DataModelType { Radyoloji, Satis, Muayene, Company } } if i write above codes i see some error: Cannot create an instance of abstract class or interface 'EfTestFactory_Company'How can i solve it? Look please below pic.

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  • Rails Controller

    - by Steve
    Hi...In Rails, is it ok to define logic in a controller with a model. For example, take there is an User Model, which is good design. 1)Leaving the UserModel with the CRUD models and moving all the other User Specific actions to a separate controller or 2)Add the user specific actions to the same UserModels Thanks :)

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  • Strategy Pattern with Type Reflection affecting Performances ?

    - by Aurélien Ribon
    Hello ! I am building graphs. A graph consists of nodes linked each other with links (indeed my dear). In order to assign a given behavior to each node, I implemented the strategy pattern. class Node { public BaseNodeBehavior Behavior {get; set;} } As a result, in many parts of the application, I am extensively using type reflection to know which behavior a node is. if (node.Behavior is NodeDataOutputBehavior) workOnOutputNode(node) .... My graph can get thousands of nodes. Is type reflection greatly affecting performances ? Should I use something else than the strategy pattern ? I'm using strategy because I need behavior inheritance. For example, basically, a behavior can be Data or Operator, a Data behavior can IO, Const or Intermediate and finally an IO behavior can be Input or Output. So if I use an enumeration, I wont be able to test for a node behavior to be of data kind, I will need to test it to be [Input, Output, Const or Intermediate]. And if later I want to add another behavior of Data kind, I'm screwed, every data-testing method will need to be changed.

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  • php : echo"", print(), printf()

    - by marc-andre menard
    Is there a better way to output data to html page with PHP ? if i like to make a div with some var in php i will write something like that print ('<div>'.$var.'</div>); or echo "'<div>'.$var.'</div>'"; what is the PROPER way to do that ? or a better way, fill a $tempvar and print it once? like that: $tempvar = '<div>'.$var.'</div>' print ($tempvar); in fact, in real life, the var will be fill with much more !

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