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  • Patterns: Local Singleton vs. Global Singleton?

    - by Mike Rosenblum
    There is a pattern that I use from time to time, but I'm not quite sure what it is called. I was hoping that the SO community could help me out. The pattern is pretty simple, and consists of two parts: A singleton factory, which creates objects based on the arguments passed to the factory method. Objects created by the factory. So far this is just a standard "singleton" pattern or "factory pattern". The issue that I'm asking about, however, is that the singleton factory in this case maintains a set of references to every object that it ever creates, held within a dictionary. These references can sometimes be strong references and sometimes weak references, but it can always reference any object that it has ever created. When receiving a request for a "new" object, the factory first searches the dictionary to see if an object with the required arguments already exits. If it does, it returns that object, if not, it returns a new object and also stores a reference to the new object within the dictionary. This pattern prevents having duplicative objects representing the same underlying "thing". This is useful where the created objects are relatively expensive. It can also be useful where these objects perform event handling or messaging - having one object per item being represented can prevent multiple messages/events for a single underlying source. There are probably other reasons to use this pattern, but this is where I've found this useful. My question is: what to call this? In a sense, each object is a singleton, at least with respect to the data it contains. Each is unique. But there are multiple instances of this class, however, so it's not at all a true singleton. In my own personal terminology, I tend to call the factory method a "global singleton". I then call the created objects "local singletons". I sometimes also say that the created objects have "reference equality", meaning that if two variables reference the same data (the same underlying item) then the reference they each hold must be to the same exact object, hence "reference equality". But these are my own invented terms, and I am not sure that they are good ones. Is there standard terminology for this concept? And if not, could some naming suggestions be made? Thanks in advance...

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  • Lisp: Determine if a list contains a predicate

    - by justkt
    As part of a homework assignment in Lisp, I am to use apply or funcall on any predicates I find. My question (uncovered in the coursework) is: how do I know when I've found a predicate in my list of arguments? I've done some basic google searching and come up with nothing so far. We're allowed to use Lisp references for the assignment - even a pointer to a good online resource (and perhaps a specific page within one) would be great!

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  • How to fix this python program?

    - by Phenom
    import math def p(n): return 393000*((288200/393000)^n * math.exp(-(288200/393000)))/math.factorial(n) print p(3) When I run it, I get the following error message: Traceback (most recent call last): File "poisson.py", line 6, in <module> print p(3) File "poisson.py", line 4, in p return 393000*((288200/393000)^n * math.exp(-(288200/393000)))/math.factoria l(n) TypeError: unsupported operand type(s) for ^: 'int' and 'float'

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  • How do you pipe output from a Ruby script to 'head' without getting a broken pipe error

    - by dan
    I have a simple Ruby script that looks like this require 'csv' while line = STDIN.gets array = CSV.parse_line(line) puts array[2] end But when I try using this script in a Unix pipeline like this, I get 10 lines of output, followed by an error: ruby lib/myscript.rb < data.csv | head 12080450 12080451 12080517 12081046 12081048 12081050 12081051 12081052 12081054 lib/myscript.rb:4:in `write': Broken pipe - <STDOUT> (Errno::EPIPE) Is there a way to write the Ruby script in a way that prevents the broken pipe exception from being raised?

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  • VS2010 debugger always breaks

    - by Paul Knopf
    In VS2010, I set a break point (from the left gutter of the editor) on a line of code. After I removed the break point, the debugger always breaks on that line of code. After starting visual studio, the debugger still breaks at the point. Thanks in advance!

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  • Python tkInter text entry validation

    - by meade
    I'm trying to validate the entry of text using Python/tkInter def validate_text(): return False text = Entry(textframe, validate="focusout", validatecommand=validate_text) where validate_text is the function - I've tried always returning False and always returning True and there's no difference in the outcome..? Is there a set of arguments in the function that I need to include? Edit - changed from NONE to focusout...still not working

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  • itertools.product eliminating repeated reversed tuples

    - by genclik27
    I asked a question yesterday and thanks to Tim Peters, it is solved. The question is here; itertools.product eliminating repeated elements The new question is further version of this. This time I will generate tuples inside of tuples. Here is an example; lis = [[(1,2), (3,4)], [(5,2), (1,2)], [(2,1), (1,2)]] When I use it in itertools.product function this is what I get, ((1, 2), (5, 2), (2, 1)) ((1, 2), (5, 2), (1, 2)) ((1, 2), (1, 2), (2, 1)) ((1, 2), (1, 2), (1, 2)) ((3, 4), (5, 2), (2, 1)) ((3, 4), (5, 2), (1, 2)) ((3, 4), (1, 2), (2, 1)) ((3, 4), (1, 2), (1, 2)) I want to change it in a way that if a sequence has (a,b) inside of it, then it can not have (b,a). In this example if you look at this sequence ((3, 4), (1, 2), (2, 1)) it has (1,2) and (2,1) inside of it. So, this sequence ((3, 4), (1, 2), (2, 1)) should not be considered in the results. As I said, I asked similar question before, in that case it was not considering duplicate elements. I try to adapt it to my problem. Here is modified code. Changed parts in old version are taken in comments. def reverse_seq(seq): s = [] for i in range(len(seq)): s.append(seq[-i-1]) return tuple(s) def uprod(*seqs): def inner(i): if i == n: yield tuple(result) return for elt in sets[i] - reverse: #seen.add(elt) rvrs = reverse_seq(elt) reverse.add(rvrs) result[i] = elt for t in inner(i+1): yield t #seen.remove(elt) reverse.remove(rvrs) sets = [set(seq) for seq in seqs] n = len(sets) #seen = set() reverse = set() result = [None] * n for t in inner(0): yield t In my opinion this code should work but I am getting error for the input lis = [[(1,2), (3,4)], [(5,2), (1,2)], [(2,1), (1,2)]]. I could not understand where I am wrong. for i in uprod(*lis): print i Output is, ((1, 2), (1, 2), (1, 2)) Traceback (most recent call last): File "D:\Users\SUUSER\workspace tree\sequence_covering _array\denemeler_buraya.py", line 39, in <module> for i in uprod(*lis): File "D:\Users\SUUSER\workspace tree\sequence_covering _array\denemeler_buraya.py", line 32, in uprod for t in inner(0): File "D:\Users\SUUSER\workspace tree\sequence_covering _array\denemeler_buraya.py", line 22, in inner for t in inner(i+1): File "D:\Users\SUUSER\workspace tree\sequence_covering _array\denemeler_buraya.py", line 25, in inner reverse.remove(rvrs) KeyError: (2, 1) Thanks,

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  • How to separate comma separeted data from csv file?

    - by Rahul
    I have opened a csv file and I want to sort each string which is comma separeted and are in same line: ex:: file : name,sal,dept tom,10000,it o/p :: each string in string variable I have a file which is already open, so I can not use "open" API, I have to use "csv.reader" which have to read one line at a time.

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  • How do I create a thread-safe write-once read-many value in Java?

    - by Software Monkey
    This is a problem I encounter frequently in working with more complex systems and which I have never figured out a good way to solve. It usually involves variations on the theme of a shared object whose construction and initialization are necessarily two distinct steps. This is generally because of architectural requirements, similar to applets, so answers that suggest I consolidate construction and initialization are not useful. By way of example, let's say I have a class that is structured to fit into an application framework like so: public class MyClass { private /*ideally-final*/ SomeObject someObject; MyClass() { someObject=null; } public void startup() { someObject=new SomeObject(...arguments from environment which are not available until startup is called...); } public void shutdown() { someObject=null; // this is not necessary, I am just expressing the intended scope of someObject explicitly } } I can't make someObject final since it can't be set until startup() is invoked. But I would really like it to reflect it's write-once semantics and be able to directly access it from multiple threads, preferably avoiding synchronization. The idea being to express and enforce a degree of finalness, I conjecture that I could create a generic container, like so: public class WoRmObject<T> { private T object; WoRmObject() { object=null; } public WoRmObject set(T val) { object=val; return this; } public T get() { return object; } } and then in MyClass, above, do: private final WoRmObject<SomeObject> someObject; MyClass() { someObject=new WoRmObject<SomeObject>(); } public void startup() { someObject.set(SomeObject(...arguments from environment which are not available until startup is called...)); } Which raises some questions for me: Is there a better way, or existing Java object (would have to be available in Java 4)? Is this thread-safe provided that no other thread accesses someObject.get() until after it's set() has been called. The other threads will only invoke methods on MyClass between startup() and shutdown() - the framework guarantees this. Given the completely unsynchronized WoRmObject container, it is ever possible under either JMM to see a value of object which is neither null nor a reference to a SomeObject? In other words, does has the JMM always guaranteed that no thread can observe the memory of an object to be whatever values happened to be on the heap when the object was allocated.

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  • Can I use rest-client to POST a binary file to HTTP without multipart?

    - by Angela
    I have tried to do the following, but the web-service is NOT REST and does not take multi-part. What do I do in order to POST the image? @response = RestClient.post('http://www.postful.com/service/upload', {:upload => { :file => File.new("#{@postalcard.postalimage.path}",'rb') } }, {"Content-Type" => @postalcard.postalimage.content_type, "Content-Length" => @postalcard.postalimage.size, "Authorization" => 'Basic xxxxxx' } # end headers ) #close arguments to Restclient.post

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  • How can I make xmlpp::DomParser less verbose on errors?

    - by Beau Simensen
    How can I make xmlpp::DomParser be less verbose on errors? Right now, if parsing fails, I get a bunch of text printed to my console and I'd just as soon have that not be visible. Entity: line 1: parser error : Opening and ending tag mismatch: feed line 1 and fed <feed><entry id='5' /></fed> I don't see a lot of options for xmlpp::DomParser but I have to believe this is something that can be disabled/tweaked.

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  • Writing csv header removes data from numpy array written below

    - by user338095
    I'm trying to export data to a csv file. It should contain a header (from datastack) and restacked arrays with my data (from datastack). One line in datastack has the same length as dataset. The code below works but it removes parts of the first line from datastack. Any ideas why that could be? s = ','.join(itertools.chain(dataset)) + '\n' newfile = 'export.csv' f = open(newfile,'w') f.write(s) numpy.savetxt(newfile, (numpy.transpose(datastack)), delimiter=', ') f.close()

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  • Can processor cores thrash each other's caches?

    - by Jørgen Fogh
    If more than one core on a processor is accessing the same memory address, will they thrash each other's caches or will some snooping protocol allow each to keep the data in L1-cache? I am interested in a general answer as well as answers for specific processors. How many layers of cache are invalidated? Will accessing another address within the same cache-line invalidate the entire line? What can you do to alleviate these problems?

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  • Problem adding eclair sources to Eclipse 3.5

    - by Oletros
    I have sync eclair sources using repo ~/eclair_sources/ In Eclipse I create a project using existent sources and I add the former folder and I have a lot of errors like thos: Description Resource Path Location Type android.R.attr cannot be resolved to a type SuggestionsAdapter.java /eclair/frameworks/base/core/java/android/app line 411 Java Problem _Original_Bitmap cannot be resolved to a type Bitmap.java /eclair/frameworks/base/tools/layoutlib/bridge/src/android/graphics line 27 Java Problem Any advise?

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  • how can i randomly print an element from a list in python

    - by lm
    So far i have this, which prints out every word in my list, but i am trying to print only one word at random. Any suggestions? def main(): # open a file wordsf = open('words.txt', 'r') word=random.choice('wordsf') words_count=0 for line in wordsf: word= line.rstrip('\n') print(word) words_count+=1 # close the file wordsf.close()

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  • Error "Create a concrete instance!"

    - by dododedodonl
    Hey All, I've got another problem in the same code... I'm getting this error: *** initialization method -initWithFormat:locale:arguments: cannot be sent to an abstract object of class NSString_RegEx: Create a concrete instance! But I don't understand the error or what I should do...

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  • Entity Framework 4 missing features?

    - by Roger Alsing
    I'm well aware that similair topics have been brought up before e.g. http://stackoverflow.com/questions/1639043/entity-framework-4-vs-nhibernate But instead of arguments like: NHibernate have been around longer and is more mature EF4 is drag n drop and not enterprisy EF4 and LinqToSql are ... I would like to see a more detailed list of features that you consider missing from EF4. Personally, I think the lack of enum support is the biggest drawback of EF4.

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  • Render {embed} for each entry in {exp:weblog:entries} loop

    - by eyelidlessness
    {exp:weblog:entries [args]} [content] {embed="path/to/sub-template" [args]} {/exp:weblog:entries} The sub-template only renders for the first entry, and the {embed} template tag is swallowed for all subsequent entries. Is there a way to make it render the sub-template for each iteration? Edit: stranger yet, if caching is enabled for the sub-template, it renders for each iteration—but, of course, the arguments on the embed tag aren't passed to subsequent iterations, as the sub-template is cached.

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  • match strings in python

    - by mesun
    Write a function, called constrainedMatchPair which takes three arguments: a tuple representing starting points for the first substring, a tuple representing starting points for the second substring, and the length of the first substring. The function should return a tuple of all members (call it n) of the first tuple for which there is an element in the second tuple (call it k) such that n+m+1 = k, where m is the length of the first substring. Complete the definition def constrainedMatchPair(firstMatch,secondMatch,length):

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