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  • GHC.Generics and Type Families

    - by jberryman
    This is a question related to my module here, and is simplified a bit. It's also related to this previous question, in which I oversimplified my problem and didn't get the answer I was looking for. I hope this isn't too specific, and please change the title if you can think if a better one. Background My module uses a concurrent chan, split into a read side and write side. I use a special class with an associated type synonym to support polymorphic channel "joins": {-# LANGUAGE TypeFamilies #-} class Sources s where type Joined s newJoinedChan :: IO (s, Messages (Joined s)) -- NOT EXPORTED --output and input sides of channel: data Messages a -- NOT EXPORTED data Mailbox a instance Sources (Mailbox a) where type Joined (Mailbox a) = a newJoinedChan = undefined instance (Sources a, Sources b)=> Sources (a,b) where type Joined (a,b) = (Joined a, Joined b) newJoinedChan = undefined -- and so on for tuples of 3,4,5... The code above allows us to do this kind of thing: example = do (mb , msgsA) <- newJoinedChan ((mb1, mb2), msgsB) <- newJoinedChan --say that: msgsA, msgsB :: Messages (Int,Int) --and: mb :: Mailbox (Int,Int) -- mb1,mb2 :: Mailbox Int We have a recursive action called a Behavior that we can run on the messages we pull out of the "read" end of the channel: newtype Behavior a = Behavior (a -> IO (Behavior a)) runBehaviorOn :: Behavior a -> Messages a -> IO () -- NOT EXPORTED This would allow us to run a Behavior (Int,Int) on either of msgsA or msgsB, where in the second case both Ints in the tuple it receives actually came through separate Mailboxes. This is all tied together for the user in the exposed spawn function spawn :: (Sources s) => Behavior (Joined s) -> IO s ...which calls newJoinedChan and runBehaviorOn, and returns the input Sources. What I'd like to do I'd like users to be able to create a Behavior of arbitrary product type (not just tuples) , so for instance we could run a Behavior (Pair Int Int) on the example Messages above. I'd like to do this with GHC.Generics while still having a polymorphic Sources, but can't manage to make it work. spawn :: (Sources s, Generic (Joined s), Rep (Joined s) ~ ??) => Behavior (Joined s) -> IO s The parts of the above example that are actually exposed in the API are the fst of the newJoinedChan action, and Behaviors, so an acceptable solution can modify one or all of runBehaviorOn or the snd of newJoinedChan. I'll also be extending the API above to support sums (not implemented yet) like Behavior (Either a b) so I hoped GHC.Generics would work for me. Questions Is there a way I can extend the API above to support arbitrary Generic a=> Behavior a? If not using GHC's Generics, are there other ways I can get the API I want with minimal end-user pain (i.e. they just have to add a deriving clause to their type)?

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  • Constructor within a constructor

    - by Chiramisu
    Is this a bad idea? Does calling a generic private constructor within a public constructor create multiple instances, or is this a valid way of initializing class variables? Private Class MyClass Dim _msg As String Sub New(ByVal name As String) Me.New() 'Do stuff End Sub Sub New(ByVal name As String, ByVal age As Integer) Me.New() 'Do stuff End Sub Private Sub New() 'Initializer constructor Me._msg = "Hello StackOverflow" 'Initialize other variables End Sub End Class

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  • How to correctly populate records from SQLlite in ListActivity?

    - by Pavel
    Hi. Can someone please tell me how can I easily display every record from sqllite in ListActivity tab? I'm kinda confused with this. Do I have to create db from my helper class in TabActivity or ListActivity or both? My db helper class is as follow: package tabs.app; import android.content.ContentValues; import android.content.Context; import android.database.Cursor; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.util.Log; public class DBAdapter { private static String DB_PATH = "/data/data/tabs.app/databases/"; public static final String KEY_ROWID = "_id"; public static final String KEY_LATITUDE = "latitude"; public static final String KEY_LONGITUDE = "longitude"; private static final String TAG = "DBAdapter"; private static final String DATABASE_NAME = "coords"; private static final String DATABASE_TABLE = "coordsStorages"; private static final int DATABASE_VERSION = 2; /* private static final String DATABASE_CREATE = "create table coordsStorage (_id integer primary key autoincrement, latitude integer not null, longitude integer not null)"; */ public Context context; private DatabaseHelper DBHelper; private SQLiteDatabase db; public DBAdapter(Context ctx) { this.context = ctx; DBHelper = new DatabaseHelper(context); } private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL("create table coordsStorages (_id integer primary key autoincrement, latitude integer not null, longitude integer not null)"); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion + ", which will destroy all old data"); db.execSQL("DROP TABLE IF EXISTS titles"); onCreate(db); } } //---opens the database--- public DBAdapter open() throws SQLException { db = DBHelper.getWritableDatabase(); return this; } //---closes the database--- public void close() { DBHelper.close(); } //---insert a title into the database--- public long insertCoords(int latitude, int longitude) { ContentValues initialValues = new ContentValues(); initialValues.put(KEY_LATITUDE, latitude); initialValues.put(KEY_LONGITUDE, longitude); return db.insert(DATABASE_TABLE, null, initialValues); } public void openDataBase() throws SQLException{ //Open the database String myPath = DB_PATH + DATABASE_NAME; db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY); } //---deletes a particular title--- public boolean deleteTitle(long rowId) { return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0; } //---retrieves all the titles--- public Cursor getAllTitles() { return db.query(DATABASE_TABLE, new String[] { KEY_ROWID, KEY_LATITUDE, KEY_LONGITUDE}, null, null, null, null, null); } //---retrieves a particular title--- public Cursor getTitle(long rowId) throws SQLException { Cursor mCursor = db.query(true, DATABASE_TABLE, new String[] { KEY_ROWID, KEY_LATITUDE, KEY_LONGITUDE}, KEY_ROWID + "=" + rowId, null, null, null, null, null); if (mCursor != null) { mCursor.moveToFirst(); } return mCursor; } //---updates a title--- /*public boolean updateTitle(long rowId, int latitude, int longitude) { ContentValues args = new ContentValues(); args.put(KEY_LATITUDE, latitude); args.put(KEY_LONGITUDE, longitude); return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0; }*/ } And Im trying to retrieve the records in TabActivity like this: public class Areas extends ListActivity { DBAdapter db; SimpleCursorAdapter mAdapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.areas_layout); db = new DBAdapter(this); db.open(); Cursor c = db.getAllTitles(); startManagingCursor(c); String[] display = new String[] { db.KEY_LATITUDE }; int[] to = new int[] { R.id.row_latitude}; /* String[] display2 = new String[] { db.KEY_LONGITUDE }; int[] to2 = new int[] { R.id.row_longitude};*/ mAdapter = new SimpleCursorAdapter(this, R.layout.areas_layout, c, display, to); setListAdapter(mAdapter); /* mAdapter2 = new SimpleCursorAdapter(this, R.layout.areas_layout, c, display2, to2); setListAdapter(mAdapter2);*/ db.close(); } /* private void fillData() { // Get all of the rows from the database and create the item list Cursor c = db.getAllTitles(); startManagingCursor(c); }*/ } Whenever I'm trying to do that the error log outputs this: 06-07 09:51:56.529: ERROR/AndroidRuntime(2034): Uncaught handler: thread main exiting due to uncaught exception 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): java.lang.RuntimeException: Unable to start activity ComponentInfo{tabs.app/tabs.app.Areas}: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list' 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2401) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.ActivityThread.startActivityNow(ActivityThread.java:2242) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:631) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.widget.TabHost.setCurrentTab(TabHost.java:317) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.widget.TabHost$2.onTabSelectionChanged(TabHost.java:127) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.widget.TabWidget$TabClickListener.onClick(TabWidget.java:346) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.View.performClick(View.java:2344) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.View.onTouchEvent(View.java:4133) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.View.dispatchTouchEvent(View.java:3672) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:850) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1712) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1202) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.Activity.dispatchTouchEvent(Activity.java:1987) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1696) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewRoot.handleMessage(ViewRoot.java:1658) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.os.Handler.dispatchMessage(Handler.java:99) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.os.Looper.loop(Looper.java:123) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.ActivityThread.main(ActivityThread.java:4203) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at java.lang.reflect.Method.invokeNative(Native Method) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at java.lang.reflect.Method.invoke(Method.java:521) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at dalvik.system.NativeStart.main(Native Method) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list' 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.ListActivity.onContentChanged(ListActivity.java:236) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:316) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.Activity.setContentView(Activity.java:1620) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at tabs.app.Areas.onCreate(Areas.java:18) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): ... 30 more 06-07 09:51:56.619: INFO/Process(51): Sending signal. PID: 2034 SIG: 3 06-07 09:51:56.619: INFO/dalvikvm(2034): threadid=7: reacting to signal 3 06-07 09:51:56.619: ERROR/dalvikvm(2034): Unable to open stack trace file '/data/anr/traces.txt': Permission denied Can someone please tell me what I'm doing wrong? Help greatly appreciated!

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  • Server.Execute - render .ASP from MVC controller action

    - by David Lively
    I need to render an ASP page to a string from an MVC controller action. I can use Server.Execute() to render a .aspx page, but not a .asp page. Here's what I'm using: public ActionResult Index() { Server.Execute("/default.asp"); return new EmptyResult(); } which returns `No http handler was found for request type 'GET'` Any suggestions? I can do something similar with with a web request, but I'd rather avoid the overhead of a loopback request.

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  • DatagridView Background does not refresh. Traces left behind.

    - by Curchy
    I have a DataGridView bound on a generic list, in .NET 3.5. When this grid is resized, there is a residual traces that is left behind on the background of the grid where there is no items. This only occurs where there is some columns that have the WrapMode attribute set to True. It seems that only the content that is wrapped is not refreshed on the background of the grid. Anybody have a workaround or a resolution for this problem?

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  • Django 5 star Reviews

    - by firststepofthejourney
    Hello All, I am new to programming and I just jumped in to Django and I need a bit of help. I downloaded the generic reviews model off of Google code and I have no clue how to implement it. Can anyone pass along some guidance on how to make this work with a 5 star ratings system? I would appreciate it. Thanks.

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  • Select...Case VB.NET to C# Equivalent

    - by Alex Essilfie
    I just started using C# and I've got a couple of issues. I hook several controls to one event handler as in the following and I want to perform a slightly different action for each control: Private Sub Button_Click(sender as Object, e as EventArgs) _ Handles button1.Click, Button2.Click 'do a general activity Select CType(sender, Button).Name Case button1.Name 'do something Case button2.Name 'do something else Case Else 'do the defalut action End Select End Sub Is there any way of doing the above select statement in C# without having to use nested ifs?

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  • Most interesting and challenging programming tasks

    - by dsimcha
    Some programmers enjoy optimizing code to make the implementation as fast as humanly possible; or golfing to make code as compact as possible. Others enjoy metaprogramming to make code generic, or designing algorithms to be asymptotically efficient. What do you find most interesting and challenging as a programmer?

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  • Handling Input with Zend Framework outside MVC

    - by Pekka
    In a classic Zend Framework MVC setup, there seems to be access to a generic _request object from within the model/view/controller instance as outlined here: $this->_request->getPost('variablename'); is this request object somehow available in a non-MVC setup as well? If yes: how would I initialize and access it?

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  • Specializating a template function that takes a universal reference parameter

    - by David Stone
    How do I specialize a template function that takes a universal reference parameter? foo.hpp: template<typename T> void foo(T && t) // universal reference parameter foo.cpp template<> void foo<Class>(Class && class) { // do something complicated } Here, Class is no longer a deduced type and thus is Class exactly; it cannot possibly be Class &, so reference collapsing rules will not help me here. I could perhaps create another specialization that takes a Class & parameter (I'm not sure), but that implies duplicating all of the code contained within foo for every possible combination of rvalue / lvalue references for all parameters, which is what universal references are supposed to avoid. Is there some way to accomplish this? To be more specific about my problem in case there is a better way to solve it: I have a program that can connect to multiple game servers, and each server, for the most part, calls everything by the same name. However, they have slightly different versions for a few things. There are a few different categories that these things can be: a move, an item, etc. I have written a generic sort of "move string to move enum" set of functions for internal code to call, and my server interface code has similar functions. However, some servers have their own internal ID that they communicate with, some use strings, and some use both in different situations. Now what I want to do is make this a little more generic. I want to be able to call something like ServerNamespace::server_cast<Destination>(source). This would allow me to cast from a Move to a std::string or ServerMoveID. Internally, I may need to make a copy (or move from) because some servers require that I keep a history of messages sent. Universal references seem to be the obvious solution to this problem. The header file I'm thinking of right now would expose simply this: namespace ServerNamespace { template<typename Destination, typename Source> Destination server_cast(Source && source); } And the implementation file would define all legal conversions as template specializations.

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  • Windows7 Installer takes priority how to move it back during installation using C#?

    - by shahjapan
    I've a custom Action on Deployment project of .NET Applicaiton, which contains custom dialogbox to enter certain parameters, on invalid parameters I've shown MessageBox.Show - but its being hide by installer window, I tried windows forms too with Activate, TopMost, Focus,bring2front, etc serveral options but it comes by default behind the windows installer window and due to this user is not able to identify why installing process is not finishing - because actually its waiting for user to read the MessageBox and press OK. I've tried to implement IWin32Window with the handler of MsiExec Process, and shown the Messagebox but still its not working, anyone has idea ??? Here is my installer.cs function defination, public override void Install(IDictionary stateSaver)

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  • Load large images into Bitmap?

    - by GuyNoir
    I'm trying to make a basic application that displays an image from the camera, but I when I try to load the .jpg in from the sdcard with BitmapFactory.decodeFile, it returns null. It doesn't give an out of memory error which I find strange, but the exact same code works fine on smaller images. How does the generic gallery display huge pictures from the camera with so little memory?

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  • rawurlencode() and urlencode() not working in CodeIgniter

    - by Keith Chason
    I am trying to encode a string into a safe url for generic purposes, and neither rawurlencode() nor urlencode() work when using CodeIgniter. I have used them and they work pefectly fine with straight PHP, but for whatever reason, it doesn't work. I haven't been able to find any others with this problem and thus no solution. Code: <a href="/search/degree/<?=rawurlencode($row->degree)?>" class="element_link"><?=$row->degree?></a>

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  • jquery javascript module architecture on a website

    - by stephan
    I want to write a module on one html site - I will never leave the site I think about two possible concurrent basic approaches: We go into the module by use only a specific function (with specific params - everything which will happen, happen there - logic, exception handling etc) We go in by using one handler-fct, which manages some kind of action & a dataArray (depending on the action also fcts will be called - but not directly maybe for exception handling) So what you prefer?!

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  • returning JSON response to a ajax call prompts file download containing the response

    - by user200018
    i am submitting a from using jQuery ajax, and server is returning json response. but instead of the script, parsing the json result, the browser is prompting me to download the json response. I have had this problem before, where i forgot to return false at the end of the event handler. But this time im clueless why this is happening. anyone has experienced this problem.. thanks

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  • How to use HTTP method DELETE on Google App Engine?

    - by Jader Dias
    I can use this verb in the Python Windows SDK. But not in production. Why? What am I doing wrong? The error message includes (only seen via firebug or fiddler) Malformed request or something like that My code looks like: from google.appengine.ext import db from google.appengine.ext import webapp class Handler(webapp.RequestHandler): def delete(self): key = self.request.get('key') item = db.get(key) item.delete() self.response.out.write(key)

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  • importing modules in app engine

    - by tanky
    Ive asked this before, but it seems i wasnt clear/detailed enough and after a week of trying im still struggling so i will try again. i am trying to use, oauth2 and ply on app engine. i have tried copying their directories into my app engine project directory (in the form ply-3.4 or brosner-python-oauth2-82a05f9) and i have tried copying the specific sub directory contained within the aforemention one. (ply or oauth2) i have tried saying import oauth2, from brosner-oauth2_python-82a05f9 import oauth and other variations on the theme, but i still cant get it to work nothing has worked. i have tried including them in app.yaml, but that seemed to create an even bigger error as my entire project wouldnt even run when i tried that. and now i have run out of things to try. the error log i am getting is as follows. INFO 2012-10-20 22:33:29,358 dev_appserver.py:2884] "GET / HTTP/1.1" 500 - WARNING 2012-10-20 22:33:58,453 py_zipimport.py:139] Can't open zipfile C:\Python27\lib\site-packages\oauth2-1.0.2-py2.7.egg: IOError: [Errno 13] file not accessible: 'C:\Python27\lib\site-packages\oauth2-1.0.2-py2.7.egg' WARNING 2012-10-20 22:33:58,453 py_zipimport.py:139] Can't open zipfile C:\Python27\lib\site-packages\ply-3.4-py2.7.egg: IOError: [Errno 13] file not accessible: 'C:\Python27\lib\site-packages\ply-3.4-py2.7.egg' WARNING 2012-10-20 22:33:58,453 py_zipimport.py:139] Can't open zipfile C:\Python27\lib\site-packages\tweepy-1.11-py2.7.egg: IOError: [Errno 13] file not accessible: 'C:\Python27\lib\site-packages\tweepy-1.11-py2.7.egg' ERROR 2012-10-20 22:34:00,015 wsgi.py:189] Traceback (most recent call last): File "C:\Program Files\Google\google_appengine\google\appengine\runtime\wsgi.py", line 187, in Handle handler = _config_handle.add_wsgi_middleware(self._LoadHandler()) File "C:\Program Files\Google\google_appengine\google\appengine\runtime\wsgi.py", line 225, in _LoadHandler handler = import(path[0]) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver_import_hook.py", line 676, in Decorate return func(self, *args, **kwargs) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver_import_hook.py", line 1850, in load_module return self.FindAndLoadModule(submodule, fullname, search_path) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver_import_hook.py", line 676, in Decorate return func(self, *args, **kwargs) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver_import_hook.py", line 1722, in FindAndLoadModule description) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver_import_hook.py", line 676, in Decorate return func(self, *args, **kwargs) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver_import_hook.py", line 1665, in LoadModuleRestricted description) File "C:\Documents and Settings\ladds\My Documents\udacity\sigh\main.py", line 3, in import ply ImportError: No module named ply INFO 2012-10-20 22:34:00,030 dev_appserver.py:2884] "GET / HTTP/1.1" 500 - thanks for any help.

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  • Summary of changes for each API level?

    - by MisterSquonk
    As the title says, are there any sources (web pages etc) of summarised changes at each API level? I have an app which I've put out to a small group of beta testers and I already fell foul of Environment.getExternalFilesDir(), which I hadn't noticed was introduced in API Level 8, when a couple of the guys tried it on Android v2.1 devices. The majority of my code should be pretty generic but it would be useful if I could find a condensed/summarised list/table or similar that I can quickly glance over.

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  • Any way to allow classes implementing IEntity and downcast to have operator == comparisons?

    - by George Mauer
    Basically here's the issue. All entities in my system are identified by their type and their id. new Customer() { Id = 1} == new Customer() {Id = 1}; new Customer() { Id = 1} != new Customer() {Id = 2}; new Customer() { Id = 1} != new Product() {Id = 1}; Pretty standard scenario. Since all Entities have an Id I define an interface for all entities. public interface IEntity { int Id { get; set;} } And to simplify creation of entities I make public abstract class BaseEntity<T> : where T : IEntity { int Id { get; set;} public static bool operator ==(BaseEntity<T> e1, BaseEntity<T> e2) { if (object.ReferenceEquals(null, e1)) return false; return e1.Equals(e2); } public static bool operator !=(BaseEntity<T> e1, BaseEntity<T> e2) { return !(e1 == e2); } } where Customer and Product are something like public class Customer : BaseEntity<Customer>, IEntity {} public class Product : BaseEntity<Product>, IEntity {} I think this is hunky dory. I think all I have to do is override Equals in each entity (if I'm super clever, I can even override it only once in the BaseEntity) and everything with work. So now I'm expanding my test coverage and find that its not quite so simple! First of all , when downcasting to IEntity and using == the BaseEntity< override is not used. So what's the solution? Is there something else I can do? If not, this is seriously annoying. Upadate It would seem that there is something wrong with my tests - or rather with comparing on generics. Check this out [Test] public void when_created_manually_non_generic() { // PASSES! var e1 = new Terminal() {Id = 1}; var e2 = new Terminal() {Id = 1}; Assert.IsTrue(e1 == e2); } [Test] public void when_created_manually_generic() { // FAILS! GenericCompare(new Terminal() { Id = 1 }, new Terminal() { Id = 1 }); } private void GenericCompare<T>(T e1, T e2) where T : class, IEntity { Assert.IsTrue(e1 == e2); } Whats going on here? This is not as big a problem as I was afraid, but is still quite annoying and a completely unintuitive way for the language to behave. Update Update Ah I get it, the generic implicitly downcasts to IEntity for some reason. I stand by this being unintuitive and potentially problematic for my Domain's consumers as they need to remember that anything happening within a generic method or class needs to be compared with Equals()

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  • How to give focus to default program of shell-opened file, from Java ?

    - by Rabarberski
    From within Java, I am opening an Excel file with the default file handler (MS Excel, in this case :-) ) using the method described in this stackoverflow question: Desktop dt = Desktop.getDesktop(); dt.open(new File(filename)); However, the Excel program doesn't get the focus. Is there any easy way to do so? Edit: There is a related stackoverflow question for C#, but I didn't find any similar Java method.

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