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  • Why the "mutable default argument fix" syntax is so ugly, asks python newbie

    - by Cawas
    Now following my series of "python newbie questions" and based on another question. Go to http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html#other-languages-have-variables and scroll down to "Default Parameter Values". There you can find the following: def bad_append(new_item, a_list=[]): a_list.append(new_item) return a_list def good_append(new_item, a_list=None): if a_list is None: a_list = [] a_list.append(new_item) return a_list So, question here is: why is the "good" syntax over a known issue ugly like that in a programming language that promotes "elegant syntax" and "easy-to-use"? Why not just something in the definition itself, that the "argument" name is attached to a "localized" mutable object like: def better_append(new_item, a_list=[].local): a_list.append(new_item) return a_list I'm sure there would be a better way to do this syntax, but I'm also almost positive there's a good reason to why it hasn't been done. So, anyone happens to know why?

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  • What to do when ServerSocket throws IOException and keeping server running

    - by s5804
    Basically I want to create a rock solid server. while (keepRunning.get()) { try { Socket clientSocket = serverSocket.accept(); ... spawn a new thread to handle the client ... } catch (IOException e) { e.printStackTrace(); // NOW WHAT? } } In the IOException block, what to do? Is the Server socket at fault so it need to be recreated? For example wait a few seconds and then serverSocket = ServerSocketFactory.getDefault().createServerSocket(MY_PORT); However if the server socket is still OK, then it is a pity to close it and kill all previously accepted connections that are still communicating. EDIT: After some answers, here my attempt to deal with the IOException. Would the implementation be guaranteeing keeping the server up and only re-create server socket when only necessary? while (keepRunning.get()) { try { Socket clientSocket = serverSocket.accept(); ... spawn a new thread to handle the client ... bindExceptionCounter = 0; } catch (IOException e) { e.printStackTrace(); recreateServerSocket(); } } private void recreateServerSocket() { while (keepRunning) { try { logger.info("Try to re-create Server Socket"); ServerSocket socket = ServerSocketFactory.getDefault().createServerSocket(RateTableServer.RATE_EVENT_SERVER_PORT); // No exception thrown, then use the new socket. serverSocket = socket; break; } catch (BindException e) { logger.info("BindException indicates that the server socket is still good.", e); bindExceptionCounter++; if (bindExceptionCounter < 5) { break; } } catch (IOException e) { logger.warn("Problem to re-create Server Socket", e); e.printStackTrace(); try { Thread.sleep(30000); } catch (InterruptedException ie) { logger.warn(ie); } } } }

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  • Getting unpredictable data into a tabular format

    - by Acorn
    The situation: Each page I scrape has <input> elements with a title= and a value= I don't know what is going to be on the page. I want to have all my collected data in a single table at the end, with a column for each title. So basically, I need each row of data to line up with all the others, and if a row doesn't have a certain element, then it should be blank (but there must be something there to keep the alignment). eg. First page has: {animal: cat, colour: blue, fruit: lemon, day: monday} Second page has: {animal: fish, colour: green, day: saturday} Third page has: {animal: dog, number: 10, colour: yellow, fruit: mango, day: tuesday} Then my resulting table should be: animal | number | colour | fruit | day cat | none | blue | lemon | monday fish | none | green | none | saturday dog | 10 | yellow | mango | tuesday Although it would be good to keep the order of the title value pairs, which I know dictionaries wont do. So basically, I need to generate columns from all the titles (kept in order but somehow merged together) What would be the best way of going about this without knowing all the possible titles and explicitly specifying an order for the values to be put in?

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  • iPhone: Error when using -(id)initWithNibName

    - by Nic Hubbard
    I am trying to use the following code, but I always get an error that I can find little information about: - (id)initWithNibName:@"MyRidesListView" bundle:nil { if ((self = [super initWithNibName:@"MyRidesListView" bundle:nil])) { // Custom initialization } return self; } Error: expected identifier before 'OBJC_STRING' token This seems like a simple method to be calling. This is for a UINavigationController. Ideas?

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  • Extremely basic PHP and Mysql

    - by fighella
    Background: I am more of a designer than a programmer, but have hacked templates for many open source CMS's (Drupal, Joomla, Wordpress) I want to start from scratch in regards to the relations of php and a mysql database. Lets assume I have a working database and php engine locally. What would be my first step to connecting to my database and creating a table... (im happy to be led to an appropriate tutorial...) Many of the tutorials I have seen start with basic php, but I would rather explore the connection between the db and the php.

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  • Learning Haskell maps, folds, loops and recursion

    - by Darknight
    I've only just dipped my toe in the world of Haskell as part of my journey of programming enlightenment (moving on from, procedural to OOP to concurrent to now functional). I've been trying an online Haskell Evaluator. However I'm now stuck on a problem: Create a simple function that gives the total sum of an array of numbers. In a procedural language this for me is easy enough (using recursion) (c#) : private int sum(ArrayList x, int i) { if (!(x.Count < i + 1)) { int t = 0; t = x.Item(i); t = sum(x, i + 1) + t; return t; } } All very fine however my failed attempt at Haskell was thus: let sum x = x+sum in map sum [1..10] this resulted in the following error (from that above mentioned website): Occurs check: cannot construct the infinite type: a = a -> t Please bear in mind I've only used Haskell for the last 30 minutes! I'm not looking simply for an answer but a more explanation of it. Thanks in advanced.

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  • Custom dropdown for CComboBox

    - by WalderFrey
    I'm trying to create a custom dropdown for a derivative of CComboBox. The dropdown will be a calendar control plus some 'hotspots', e.g. So I figure the best way to achieve this is to have a simple CWnd-derived class which acts as the parent to the calendar control, and have it paint the hotspots itself. The window needs to be a popup window - I think - rather than a child window so that it isn't clipped. But doing this causes the dialog (on which the combobox control is placed) to stop being the topmost (foreground?) window, leading to its frame being drawn differently: This spoils the illusion that the dropdown is part of the combobox since its acting more like a modal dialog at this point. Any suggestions on how I make the custom dropdown behave like the regular dropdown? Are there any other pitfalls I need to watch out for, e.g. focus and mouse capture issues?

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  • How to learn how to program?

    - by twinbornJoint
    I would like to know the best methods for learning to program. I've been directed towards the Python language because I was told it is good for beginners. I ultimately want to make games for OS X/iPhone. My problem is that I understand what I read but I can't apply my knowledge to anything. I am a programming noob. Should I stick with Python? (is there a better language I should be learning?) Where can I learn programming theory? I get very hyper when reading my book sometimes, any tips on staying calm and focusing? What are effective ways to learn how to program? Are there standard exercises for programming? (I feel solving problems helps my understanding immensely) Ultimately I feel like I am in a never ending tunnel that leads me no where. It feels like I am just completely unable to pursue anything in the world of programming, yet it is something I want to do very much. Thanks.

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  • Form (or Formset?) to handle multiple table rows in Django

    - by Ben
    Hi, I'm working on my first Django application. In short, what it needs to do is to display a list of film titles, and allow users to give a rating (out of 10) to each film. I've been able to use the {{ form }} and {{ formset }} syntax in a template to produce a form which lets you rate one film at a time, which corresponds to one row in a MySQL table, but how do I produce a form that iterates over all the movie titles in the database and produces a form that lets you rate lots of them at once? At first, I thought this was what formsets were for, but I can't see any way to automatically iterate over the contents of a database table to produce items to go in the form, if you see what I mean. Currently, my views.py has this code: def survey(request): ScoreFormSet = formset_factory(ScoreForm) if request.method == 'POST': formset = ScoreFormSet(request.POST, request.FILES) if formset.is_valid(): return HttpResponseRedirect('/') else: formset = ScoreFormSet() return render_to_response('cf/survey.html', { 'formset':formset, }) And my survey.html has this: <form action="/survey/" method="POST"> <table> {{ formset }} </table> <input type = "submit" value = "Submit"> </form> Oh, and the definition of ScoreForm and Score from models.py are: class Score(models.Model): movie = models.ForeignKey(Movie) score = models.IntegerField() user = models.ForeignKey(User) class ScoreForm(ModelForm): class Meta: model = Score So, in case the above is not clear, what I'm aiming to produce is a form which has one row per movie, and each row shows a title, and has a box to allow the user to enter their score. If anyone can point me at the right sort of approach to this, I'd be most grateful. Thanks, Ben

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  • strange error in haskell about indentation of if-then-else

    - by Drakosha
    I have the following code: foo :: Int -> [String] -> [(FilePath, Integer)] -> IO Int foo _ [] _ = return 4 foo _ _ [] = return 5 foo n nameREs pretendentFilesWithSizes = do result <- (bar n (head nameREs) pretendentFilesWithSizes) if result == 0 then return 0 -- <========================================== here is the error else foo n (tail nameREs) pretendentFilesWithSizes I get an error on the line with the comment above, the error is: aaa.hs:56:2: parse error (possibly incorrect indentation) I'm working with emacs, there's no spaces, and i do not understand what did i do wrong.

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  • Python regex on list

    - by Peter Nielsen
    Hi there I am trying to build a parser and save the results as an xml file but i have problems.. For instance i get a TypeError: expected string or buffer when i try to run the code.. Would you experts please have a look at my code ? import urllib2, re from xml.dom.minidom import Document from BeautifulSoup import BeautifulSoup as bs osc = open('OSCTEST.html','r') oscread = osc.read() soup=bs(oscread) doc = Document() root = doc.createElement('root') doc.appendChild(root) countries = doc.createElement('countries') root.appendChild(countries) findtags1 = re.compile ('<h1 class="title metadata_title content_perceived_text(.*?)</h1>', re.DOTALL | re.IGNORECASE).findall(soup) findtags2 = re.compile ('<span class="content_text">(.*?)</span>', re.DOTALL | re.IGNORECASE).findall(soup) for header in findtags1: title_elem = doc.createElement('title') countries.appendChild(title_elem) header_elem = doc.createTextNode(header) title_elem.appendChild(header_elem) for item in findtags2: art_elem = doc.createElement('artikel') countries.appendChild(art_elem) s = item.replace('<P>','') t = s.replace('</P>','') text_elem = doc.createTextNode(t) art_elem.appendChild(text_elem) print doc.toprettyxml()

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  • magento - webserver question

    - by WANNABE
    I've uploaded the Magento installation file to my hosting and I've been told to go to the URL you uploaded it to using you browser, then the installation wizard will run you through the processes. I uploaded to /home/domain/public_html/magneto What URL should I use to access it? Thanks in advance

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  • [Delphi] How would you refactor this code?

    - by Al C
    This hypothetical example illustrates several problems I can't seem to get past, even though I keep trying!! ... Suppose the original code is a long event handler, coded in the UI, triggered when a user clicks a cell in a grid. Expressed as pseudocode it's: if Condition1=true then begin //loop through every cell in row, //if aCell/headerCellValue>1 then //color aCell red end else if Condition2=true then begin //do some other calculation adding cell and headerCell values, and //if some other product>2 then //color the whole row green end else show an error message I look at this and say "Ah, refactor to the strategy pattern! The code will be easier to understand, easier to debug, and easier to later extend!" I get that. And I can easily break the code into multiple procedures. The problem is ultimately scope related. Assume the pseudocode makes extensive use of grid properties, values displayed in cells, maybe even built-in grid methods. How do you move all that to another unit, without referencing the grid component in the UI--which would break all the "rules" about loose coupling that make OOP valuable? ... I'm really looking forward to responses. Thanks, as always -- Al C.

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  • Is there a difference here?

    - by HotHead
    Please consider following code: 1. uint16 a = 0x0001; if(a < 0x0002) { // do something } 2. uint16 a = 0x0001; if(a < uint16(0x0002)) { // do something } 3. uint16 a = 0x0001; if(a < static_cast<uint16>(0x0002)) { // do something } 4. uint16 a = 0x0001; uint16 b = 0x0002; if(a < b) { // do something } What compiler does in backgorund and what is the best (and correct) way to do above testing? p.s. sorry, but I couldn't find the better title :) Thank you in advance!

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  • Blogger Template: how to change the color of the border css

    - by Lirik
    Hi, I'm trying to change the borders in the style sheet of the template on my blog, but I've never done anything with css so I'm a little bit at a loss... I want to keep the dark background, but I want to create a small border with a slightly different color around my postings. If my guess is correct, then I should modify some of these definitions: body { background:$bgcolor; margin:0; color:$textcolor; font: x-small "Trebuchet MS", Trebuchet, Verdana, Sans-serif; font-size/* */:/**/small; font-size: /**/small; text-align: center; } a:link { color:$linkcolor; text-decoration:none; } a:visited { color:$visitedlinkcolor; text-decoration:none; } a:hover { color:$titlecolor; text-decoration:underline; } a img { border-width:0; } Here is a pastie with the entire template I'm using: http://pastie.org/932535 Is there a quick way to achieve the desired effect? Your help is appreciated!

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  • Blackberry - Disable Save option in BasicEditField ??

    - by chethan
    I am using a basiceditfield to take input from the user to do some simple string search. But if i type a few letters and wish to go back without continuing the search, it automatically asks me whether to save the contents of the field. I don want this to happen. Can i in any way disable the "Changes made!-save-discard-cancel" option in basiceditfield(or any editfield for that matter)????please help!!!

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  • What makes you want to learn Common Lisp? What do you want from it?

    - by JasonFruit
    I'm working on a toolkit (sort of a live-CD Lisp-in-a-Box) for people new to Common Lisp, and I want to make sure it is broadly satisfying. What is attractive to you about Lisp? What do/did/would you need to get you started and keep you interested? What I have so far: SBCL 10.22, Emacs 22.3, SLIME, and LTK bundled together and configured on a Linux live-CD that boots entirely to RAM. I've now released the result of this; it is available at the Thnake website.

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  • Java: How can a constructor return a value?

    - by HH
    $ cat Const.java public class Const { String Const(String hello) { return hello; } public static void main(String[] args) { System.out.println(new Const("Hello!")); } } $ javac Const.java Const.java:7: cannot find symbol symbol : constructor Const(java.lang.String) location: class Const System.out.println(new Const("Hello!")); ^ 1 error

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  • Recursive function causing a stack overflow

    - by dbyrne
    I am trying to write a simple sieve function to calculate prime numbers in clojure. I've seen this question about writing an efficient sieve function, but I am not to that point yet. Right now I am just trying to write a very simple (and slow) sieve. Here is what I have come up with: (defn sieve [potentials primes] (if-let [p (first potentials)] (recur (filter #(not= (mod % p) 0) potentials) (conj primes p)) primes)) For small ranges it works fine, but causes a stack overflow for large ranges: user=> (sieve (range 2 30) []) [2 3 5 7 11 13 17 19 23 29] user=> (sieve (range 2 15000) []) java.lang.StackOverflowError (NO_SOURCE_FILE:0) I thought that by using recur this would be a non-stack-consuming looping construct? What am I missing?

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