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  • What is the difference between "a is b" and "id(a) == id(b)" in Python?

    - by bp
    The id() inbuilt function gives... an integer (or long integer) which is guaranteed to be unique and constant for this object during its lifetime. The is operator, instead, gives... object identity So why is it possible to have two objects that have the same id but return False to an is check? Here is an example: >>> class Test(): ... def test(): ... pass >>> a = Test() >>> b = Test() >>> id(a.test) == id(b.test) True >>> a.test is b.test False A more troubling example: (continuing the above) >>> b = a >>> b is a True >>> b.test is a.test False >>> a.test is a.test False

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  • Easy way to cast an object array into another type in C#

    - by Na7coldwater
    I want to be able to be able to quickly cast an array of objects to a different type, such as String, but the following code doesn't work: String[] a = new String[2]; a[0] = "Hello"; a[1] = "World"; ArrayList b = new ArrayList(a); String[] c = (String[]) b.ToArray(); And I don't want to have to do this: String[] a = new String[2]; a[0] = "Hello"; a[1] = "World"; ArrayList b = new ArrayList(a); Object[] temp = b.ToArray(); Object[] temp = b.ToArray(); String[] c = new String[temp.Length]; for(int i=0;i<temp.Length;i++) { c[i] = (String) temp[i]; } Is there an easy way to do this without using a temporary variable?

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  • In-memory data structure that supports boolean querying

    - by sanity
    I need to store data in memory where I map one or more key strings to an object, as follows: "green", "blue" -> object1 "red", "yellow" -> object2 I need to be able to efficiently receive a list of objects, where the strings match some boolean criteria, such as: ("red" OR "green") AND NOT "blue" I'm working in Java, so the ideal solution would be an off-the-shelf Java library. I am, however, willing to implement something from scratch if necessary. Anyone have any ideas? I'd rather avoid the overhead of an in-memory database if possible, I'm hoping for something comparable in speed to a HashMap (or at least the same order of magnitude).

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  • Count Records in Listing View

    - by 47
    I have these two models: class CommonVehicle(models.Model): year = models.ForeignKey(Year) series = models.ForeignKey(Series) engine = models.ForeignKey(Engine) body_style = models.ForeignKey(BodyStyle) ... class Vehicle(models.Model): objects = VehicleManager() stock_number = models.CharField(max_length=6, blank=False) vin = models.CharField(max_length=17, blank=False) common_vehicle = models.ForeignKey(CommonVehicle) .... What I want to do is to have a count of how many times a given CommonVehicle object is used in the Vehicle class. So far my attempts are giving me one number, which is a total of all the records. How can I have the count being the total appearances for each CommonVehicle

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  • Solve Physics exercise by brute force approach..

    - by Nils
    Being unable to reproduce a given result. (either because it's wrong or because I was doing something wrong) I was asking myself if it would be easy to just write a small program which takes all the constants and given number and permutes it with a possible operators (* / - + exp(..)) etc) until the result is found. Permutations of n distinct objects with repetition allowed is n^r. At least as long as r is small I think you should be able to do this. I wonder if anybody did something similar here..

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  • Rails - How to secure foreign keys and still allow association selection

    - by Bryce
    For simplicity, assume that I have a simple has-many-through relationship class User < ActiveRecord::Base has_many :courses, :through => :registrations end class Registration < ActiveRecord::Base belongs_to :user belongs_to :course end class Course < ActiveRecord::Base has_many :users, :through => :registrations end I want to keep my app secure, so I use attr_accessible to whitelist my attributes. My question is twofold: How would I set up my whitelist attributes such that I could create a new Registration object through a form (passing in :user and :course, but not risk allowing those foreign keys to be maliciously updated later? How would I set up my validations such that both belongs_to associations are required BUT also allow for Registration objects to be created in nested forms?

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  • Is this the right way of handling command line arguments?

    - by shadyabhi
    ask_username = True ask_password = True ask_message = True ask_number = True def Usage(): print '\t-h, --help: View help' print '\t-u, --username: Username' print '\t-p, --password: Password' print '\t-n, --number: numbber to send the sms' print '\t-m, --message: Message to send' sys.exit(1) opts, args = getopt(sys.argv[1:], 'u:p:m:n:h',["username=","password=","message=","number=","help"]) print opts, args for o,v in opts: if o in ("-h", "--help"): Usage() elif o in ("-u", "--username"): username = v ask_username = False elif o in ("-p", "--password"): passwd = v ask_password = False elif o in ("-m", "--message"): message = v ask_message = False elif o in ("-n", "--number"): number = v ask_number = False #Credentials taken here if ask_username: username = raw_input("Enter USERNAME: ") if ask_password: passwd = getpass() if ask_message: message = raw_input("Enter Message: ") if ask_number: number = raw_input("Enter Mobile number: ") I dont think it is, because I am using 4 objects just for checking if command line argument was provided... Guide me with the best way of doing it..

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  • Multiple row insertion in a faster way

    - by Cyborgo
    Hi, I am using rails and I am trying to insert new rows into the table. The data comes from a text file and I created hash with one of the attribute as key. Then I find all the keys that are currently not in the table. Then I need to insert all of them into the table with all the attributes that I saved in hash. newvals.each{ |x| author = Author.create(:first => x, :second => hash[x][0], :third => hash[x][1]) author.save } This has lot of overhead as it makes an SQL update one at time. The newals array is usually quite big around the size of 20-30k. I know create can insert multiple objects at once, but I cant seem to figure out how. Is there any way to get this done. Thanks.

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  • .NET project: unified wrapper for object databases.

    - by Steve
    I am considering doing a project which would provide unified API and tools (import/export, etc.) for object databases (e.g. Caché, Objectivity) for .NET. It would provide: schema generation from CLR classes, generation of C# classes from given OODBMs schema, API for deleting, creating and updating objects, Linq provider, API for calling object's methods on DB server, some of OODBMs provide some kind of SQL support, so API for this, providers for Caché and Objectivity in first phase. Does any project which implements any of above exist? Can this be achieved with NHibernate dialects? or are OODBMs so different than RDBMs that it worth doing separate framework for them?

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  • Getting the last member of a group on an intermediary M2M

    - by rh0dium
    If we look at the existing docs, what is the best way to get the last member added? This is similar to this but what I want to do is to be able to do this. group = Group.objects.get(id=1) group.get_last_member_added() #This is by ('-date_added') <Person: FOO> I think the best way is through a manager but how do you do this on an intermediary model? class Person(models.Model): name = models.CharField(max_length=128) def __unicode__(self): return self.name class Group(models.Model): name = models.CharField(max_length=128) members = models.ManyToManyField(Person, through='Membership') def __unicode__(self): return self.name class Membership(models.Model): person = models.ForeignKey(Person) group = models.ForeignKey(Group) date_joined = models.DateField() invite_reason = models.CharField(max_length=64)

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  • Java synchronizing static list ?

    - by JavaUser
    Hi, In a Java class , i am having a static list so this list is shared across all the objects of this class.The business logic in this class will run periodically which is invoked by some method with out passing instance parameters.Now I want to invoke this run method based on the list(I will add some vales into this list based on JMS) ,this list may empty sometimes and after finishing the run , i am emptying this list.Now my question is , whether I need to synchronize this list or not? Also let me know is there any other way to pass value in one object instance(Thread1) to other object instance (Thread2) other than having Static variable(static list)? Thx

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  • i have a arraylist where i am verifying particular object is existing or not but even it exists it always returns false

    - by Raghavender Reddy
    hi i have class called userdata which returns the Userarraylist which is of type User. when ever i try to use contains method to check particular property is existing or not it always returns false why? Actually i want the array list to be generic which should return the objects that are set in array list. String className = data.getUserData().get(0).getClass().getSimpleName(); if(className.equalsIgnoreCase("User")) { ArrayList<User> userdata=new ArrayList(); userdata = data.getUserData(); System.out.println(data.getUserData().contains(u.getUserId())); if(userdata.contains(u.getUserName())) { System.out.println(userdata.get(0).getEmailId()); } }

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  • How to invoke a Servlet (doGet) in a web application on startup?

    - by Dan
    I need to invoke a Servlet on application startup since it contains some application initialization logic. I know I can set load-on-startup configuration, but this will only invoke Servlet’s init method. I need to invoke a doGet method and pass some Url parameters to it. Servlet doGet method expects ServletRequest and ServletResponse objects. Also, since this is clustered application, I need to know exactly what node I am accessing (since one option is just to open a socket and invoke a Servlet). What is the best option to perform this?

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  • What machine learning algorithms can be used in this scenario?

    - by ExceptionHandler
    My data consists of objects as follows. Obj1 - Color - shape - size - price - ranking So I want to be able to predict what combination of color/shape/size/price is a good combination to get high ranking. Or even a combination could work like for eg: in order to get good ranking, the alg predicts best performance for this color and this shape. Something like that. What are the advisable algorithms for such a prediction? Also may be if you can briefly explain how I can approach towards the model building I would really appreciate it. Say for eg: my data looks like Blue pentagon small $50.00 #5 Red Squre large $30.00 #3 So what is a useful prediction model that I should look at? What algorithm should I try to predict like say highest weightage is for price followed by color and then size. What if I wanted to predict in combinations like a Red small shape is less likely to higher rank compared to pink small shape . (In essence trying to combine more than one nominal values column to make the prediction)

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  • Ojective C Class or struct?

    - by Scott Pendleton
    I have a class Song with properties Title, Key, Artist, etc. There are no methods. I loop through a database of song information and create a Song object for each, populating the properties, and then store the Song objects in an NSArray. Then I thought, why not just have a struct Song with all those same properties instead of a class Song. Doing so would eliminate the class files, the #import Song line in the using class's .m file, and the need to alloc, init, release. On the other hand, I'd have to put the struct definition in every class that might need it. (Unless there's some globally accessible location -- is there?) Also, can a struct be stored in an NSArray?

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  • Count function calls by name or signature. Gcc, C++

    - by MajesticRa
    I have some c++ written package. Linux, gcc. I can modify compilation process (change Makefile, flags, etc.), but can not change C++ source code. One runs the package with different parameters, it does a job and exits. How to count: 1) Number of calls of function with specific name? 2) Number of calls of functions with specific signature? 3) Number of calls of functions where one of the parameters is of specific type i.e. std::string (type is specified by signature)? 4) and extra Number of calls of functions of STL objects, i.e. std::string copy constructor? (I mean count a number of calls during the run. ) I thought to do it with GDB, but I found it very tough to do (1) and have not found how to do (2)-(4) at all. All acceptable answers I will write here for humanity.

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  • Why people define class, trait, object inside another object in Scala?

    - by Zwcat
    Ok, I'll explain why I ask this question. I begin to read Lift 2.2 source code these days. In Lift, I found that, define inner class and inner trait are very heavily used. object Menu has 2 inner traits and 4 inner classes. object Loc has 18 inner classes, 5 inner traits, 7 inner objects. There're tons of codes write like this. I wanna to know why the author write it like this. Is it because it's the author's personal taste or a powerful use of language feature?

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  • Common strategies to deal with rounding errors in currency-intensive soft?

    - by Max
    What is your advice on: compensation of accumulated error in bulk math operations on collections of Money objects. How is this implemented in your production code? (things like variable rounding, etc...) theory behind rounding in accountancy. any literature on topic. I currently read Fowler. He mentions Money type, but says nothing on strategies. Older posts on money-rounding (here, and here) do not provide a details and formality I need. Thanks for help.

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  • Can I play any Buffer only once at a given time?

    - by mystify
    From the OpenAL documentation: The basic OpenAL objects are a Listener, a Source, and a Buffer. There can be a large number of Buffers, which contain audio data. Each buffer can be attached to one or more Sources My problem is, that I have one sound file which I need to play multiple times per second, at the same time. The sound is 2 seconds long. So it will overlap. Would I need multiple filled buffers for this (= multiple times that sound in memory)? If I would attach one Buffer to multiple Sources, would I be able to play the sound 10 times, overlapping itself, with just one copy in memory? Or would I still have to deal with 10 copies of that sound in memory?

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  • Makefile won't copy .o to obj/ and target to bin/ folders

    - by about blank
    I'm trying to write a Makefile which will copy its target and objects to bin/ and obj/ directories, respectively. Yet, when I try to run it I get the following error: nasm -f elf64 -g -F stabs main.asm -l spacelander.lst ld -o spacelander obj/main.o ld: cannot find obj/main.o: No such file or directory make: *** [spacelander] Error 1 Why is this happening? Update I noticed when I posted the error that it was due to white spacing errors. After taking care of those, I still get the new error I replaced with the old one I mentioned prior. What is this?? Update 2 Posted -d flag output below Makefile source. Source ASM := nasm ARGS := -f FMT := elf64 OPT := -g -F stabs SRC := main.asm OBJDIR := obj TARGETDIR := bin OBJ := $(addprefix $(OBJDIR)/,$(patsubst %.asm, %.o, $(wildcard *.asm))) TARGET := spacelander .PHONY: all clean all: $(OBJDIR) $(TARGET) $(OBJDIR): mkdir $(OBJDIR) $(OBJDIR)/%.o: $(SRC) $(ASM) $(ARGS) $(FMT) $(OPT) $(SRC) -l $(TARGET).lst $(TARGET): $(OBJ) ld -o $(TARGET) $(OBJ) clean: @rm -f $(TARGET) $(wildcard *.o) @rm -rf $(OBJDIR) make -d Output - NOTE: output is too many characters for body, thus is pastebinned http://pastebin.com/3bctGJxs

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  • Throwing special type of exception to terminate unit test

    - by trendl
    Assume I want to write a unit test to test a particular piece of functionality that is implemented within a method. If I wanted to execute the method completely, I would have to do some extra set up work (mock objects expectations etc.). Instead of doing that I use the following approach: - I set up the expectations I'm interested in verifying and then make the tested method throw a special type of exception (e.g. TerminateTestException). - Further down in the unit test I catch the exception and verify the mock object expectations. It works fine but I'm not sure it is good practice. I do not do this regularly, only in cases where it saves me time and effort. One thing that comes to mind as an argument against using this is that throwing exceptions takes long time so the tests execute slower than if I used a different approach.

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  • memory leak in Zend_Db_Table_Row?

    - by Vincenzo
    This is the code I have: <?php $start = memory_get_usage(); $table = new Zend_Db_Table('user'); for ($i = 0; $i < 5; $i++) { $row = $table->createRow(); $row->name = 'Test ' . $i; $row->save(); unset($row); echo (memory_get_usage() - $start) . "\n"; } This is what I see: 90664 93384 96056 98728 101400 Isn't it a memory leak? When I have 500 objects to insert into DB in one script I'm getting memory overflow. Can anyone help?

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  • RSpec leaves record in test database

    - by DMiller
    Whenever I run a user test, RSpec leaves the Fabricated user in the test database after the test has completed, which is messing up my other tests. I will do a rake db:test:prepare, but when I run my tests again, the record is recreated in my database. I have no idea why this is happening. It only happens with user objects. In my spec_helper file I even have: config.use_transactional_fixtures = true Here is an example test that creates a record: it "creates a password reset token for the user" do alice = Fabricate(:user) post :create, email: alice.email expect(assigns(alice.password_reset_token)).to_not eq(nil) end Fabricator: Fabricator(:user) do email { Faker::Internet.email } password 'password' name { Faker::Name.name } end Could this have anything to do with my users model?

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  • Using temporary arrays to cut down on code - inefficient?

    - by tommaisey
    I'm new to c++ (and SO) so sorry if this is obvious. I've started using temporary arrays in my code to cut down on repetition and to make it easier to do the same thing to multiple objects. So instead of: MyObject obj1, obj2, obj3, obj4; obj1.doSomming(arg); obj2.doSomming(arg); obj3.doSomming(arg); obj4.doSomming(arg); I'm doing: MyObject obj1, obj2, obj3, obj4; MyObject* objs[] = {&obj1, &obj2, &obj3, &obj4}; for (int i = 0; i !=4; ++i) objs[i]->doSomming(arg); Is this detrimental to performance? Like, does it cause unnecessary memory allocation? Is it good practice? Thanks.

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  • Tied up with injection implemented with setter functions

    - by puudeli
    Hi, I'm trying to use Scala as part of an existing Java application and now I run into an issue with dependencies injected with a setter method (no DI frameworks in this part of code). How is this handled in a Scala way? In Scala both val and var require to be initialized when declared but I can't do that, since the Java setters inject objects that implement a certain interface and interfaces are abstract and can not be instantiated. class ScalaLogic { var service // How to initialize? def setService (srv: OutputService) = { service = srv } Is there a way to initialize the var service so that I can later assign a dependency into it? It should be lexically scoped to be visible in the whole class.

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