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• Empty dict-like collection problem in SQLAlchemy

  - by maksymko

  I have a mapping in SQLAlchemy that looks like this: t_property_value = sa.Table('property_value', MetaData, autoload = True, autoload_with = engine) orm.mapper(PropertyValue, t_property_value) t_estate = sa.Table('estate', MetaData, autoload = True, autoload_with = engine) orm.mapper(Estate, t_estate, properties = dict( property_hash = orm.relation(PropertyValue, collection_class = column_mapped_collection(t_property_value.c.property_id)) )) Now, everything seems to be fine, when I load the Estate object and it has some relations to PropertyValue objects. However, when it does not, then property_hash attribute is None, instead of being something dict-like, so I can not add new relations like this: estate.property_hash[prop_id] = PropertyValue(...) because I get the "'NoneType' object does not support item assignment" error. So, is there any way to force SQLAlchemy to create proper empty collection?

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• Can I use memcpy in C++ to copy classes that have no pointers or virtual functions

  - by Shane MacLaughlin

  Say I have a class, something like the following; class MyClass { public: MyClass(); int a,b,c; double x,y,z; }; #define PageSize 1000000 MyClass Array1[PageSize],Array2[PageSize]; If my class has not pointers or virtual methods, is it safe to use the following? memcpy(Array1,Array2,PageSize*sizeof(MyClass)); The reason I ask, is that I'm dealing with very large collections of paged data, as decribed here, where performance is critical, and memcpy offers significant performance advantages over iterative assignment. I suspect it should be ok, as the 'this' pointer is an implicit parameter rather than anything stored, but are there any other hidden nasties I should be aware of?

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• Can I improve performance by refactoring SQL commands into classes?

  - by Matthew Jones

  Currently, my entire website does updating from SQL parameterized queries. It works, we've had no problems with it, but it can occasionally be very slow. I was wondering if it makes sense to refactor some of these SQL commands into classes so that we would not have to hit the database so often. I understand hitting the database is generally the slowest part of any web application For example, say we have a class structure like this: Project (comprised of) Tasks (comprised of) Assignments Where Project, Task, and Assignment are classes. At certain points in the site you are only working on one project at a time, and so creating a Project class and passing it among pages (using Session, Profile, something else) might make sense. I imagine this class would have a Save() method to save value changes. Does it make sense to invest the time into doing this? Under what conditions might it be worth it?

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• Can I improve performance by refactoring SQL commands into C# classes?

  - by Matthew Jones

  Currently, my entire website does updating from SQL parameterized queries. It works, we've had no problems with it, but it can occasionally be very slow. I was wondering if it makes sense to refactor some of these SQL commands into classes so that we would not have to hit the database so often. I understand hitting the database is generally the slowest part of any web application For example, say we have a class structure like this: Project (comprised of) Tasks (comprised of) Assignments Where Project, Task, and Assignment are classes. At certain points in the site you are only working on one project at a time, and so creating a Project class and passing it among pages (using Session, Profile, something else) might make sense. I imagine this class would have a Save() method to save value changes. Does it make sense to invest the time into doing this? Under what conditions might it be worth it?

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• variable being weirdly deleted

  - by calccrypto

  im having a weird problem with one variable: its not being recognized but its still printing. i would post my code, but it is massive. the basic idea is: # pseudocode def function(stuff): <do stuff> # These are the only 2 conditions if tag == 3: pka = <a string> if tag == 4: pka = <a string> print pka # (1) print pka # (2) <do stuff not modifying pka> print pka # (3) if pka == 'RSA': <do stuff> elif pka == 'DSA': <do stuff> my code will error at (2). however, it will print out (1), (2), and (3), all of which are the same. is there any general explanation of why this is happening? if my code is really needed, i will post it, but otherwise, i would rather not due to its size update: now the code will error at the if statement after (3), saying UnboundLocalError: local variable 'pka' referenced before assignment even though (1),(2),(3) just printed

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• Forcing a templated object to construct from a pointer

  - by SalamiArmi

  I have a fictional class: template<typename T> class demonstration { public: demonstration(){} ... T *m_data; } At some point in the program's execution, I want to set m_data to a big block of allocated memory and construct an object T there. At the moment, I've been using this code: void construct() { *m_data = T(); } Which I've now realised is probably not the best idea... wont work under certain cirumstances, if T has a private assignment operator for example. Is there a normal/better way to do what I'm attempting here?

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• Basic help needed with pointers

  - by sbsp

  Hi, i asked some time ago on an account i cant remember how to manipulate basic pointers and someone gave me a really good demo for example char *ptr = hello (hello = a char array) so now *ptr is pointing at h ptr++ = moves the ptr to point at the next element, to get its value i do *ptr and that gives me e ok so far i hope :D but now i need to manipulate a char **ptr and was wondering how i do this in a way that mimmicks the effects of a 2d array? some basic tips would be much appreciated as i need to do an assignment that has a **ptr to immitate a 2d array and without knowing how it does this first means i cant even solve it on paper (for example, how do you dereference a **ptr, how do you get [x][y] values etc) thanks

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• Sql Server performance

  - by Jose

  I know that I can't get a specific answer to my question, but I would like to know if I can find the tools to get to my answer. Ok we have a Sql Server 2008 database that for the last 4 days has had moments where for 5-20 minutes becomes unresponsive for specific queries. e.g. The following queries run in different query windows simultaneously have the following results SELECT * FROM Assignment --hangs indefinitely SELECT * FROM Invoice -- works fine Many of the tables have non-clustered indexes to help speed up SELECTs Here's what I know: 1) The same query will either hang indefinitely or run normally. 2) In Activity Monitor in the processes tab there are normally around 80-100 processes running I think that what's happening is 1) A user updates a table 2) This causes one or more indexes to get updated 3) Another user issues a select while the index is updating Is there a way I can figure out why at a specific moment in time SQL Server is being unresponsive for a specific query?

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• LINQ to SQl updating primary key field?

  - by Curtis White

  I have a linq to sql table/class that uses a GUID as both a primary key and as foreign key. This problem came up when factoring some code that previously worked. The exception generated is "Operation is not valid due to the current state of the object." The process I use is as such: aspnet_User user() = new aspnet_User(); aspnet_user.childTable = new childTable(); .. set some properties user.Insert() -> my custom method ... @ my custom method using (mycontext dc = new context() ) { user.childTable.ID = (Guid)myNewlyCreatedGuid; } The exception occurs on the assignment childTable.set_UserId().

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• What is the best method of assessment for computer science students?

  - by Gavimoss

  This question is a bit more philosophical so feel free to remove if you like but it's been bugging me for the last 4 years! As a final year student I find that exams can be often be passed with a couple of days of cramming, without necessarily retaining or understanding the content i.e. a regurgitation of lecture notes is often enough to gain high marks. A friend of mine is about to graduate with an honours degree whose final year evaluation was based solely on practical work (a project, assignment marks and the creation of a poster) yet all of this work could have been completed by a third party. Personally I don't think either of these methods of assessment is sufficient as I am currently on track for a 1st class honours in artificial intelligence and computer science and believe this is mostly due to my skill in passing exams not my skill as a programmer or my vast in depth knowledge of any of the subjects I have "studied". Surely there is a better way to assess our skills - isn't there?

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• Using charAt in java

  - by ThuL?nå F?rñ?nDö

  This is my assignment: Write a program where the user enters a string, and the program echoes it to the monitor with one character per line: C:\>java LinePerChar Enter a string: Octopus O c t o p u s I have tried, but I'm getting some compilation errors. Here's my code: import java.util.*; class CharactorEcho{ public static void main(String args []){ Scanner sc = new Scanner(System.in); System.out.println("Enter a string :"); try { String inputString = sc.nextLine(); for(int i=0; i < sc.length(); i++) { char c = inputString.charAt(i); System.out.println("" + c); } } catch(IOException e) { } } }

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• Python If Statement Defaults to an elif

  - by Brad Carvalho

  Not sure why my code is defaulting to this elif. But it's never getting to the else statement. Even going as far as throwing index out of bound errors in the last elif. Please disregard my non use of regex. It wasn't allowed for this homework assignment. The problem is the last elif before the else statement. Cheers, Brad if item == '': print ("%s\n" % item).rstrip('\n') elif item.startswith('MOVE') and not item.startswith('MOVEI'): print 'Found MOVE' elif item.startswith('MOVEI'): print 'Found MOVEI' elif item.startswith('BGT'): print 'Found BGT' elif item.startswith('ADD'): print 'Found ADD' elif item.startswith('INC'): print 'Found INC' elif item.startswith('SUB'): print 'Found SUB' elif item.startswith('DEC'): print 'Found DEC' elif item.startswith('MUL'): print 'Found MUL' elif item.startswith('DIV'): print 'Found DIV' elif item.startswith('BEQ'): print 'Found BEQ' elif item.startswith('BLT'): print 'Found BLT' elif item.startswith('BR'): print 'Found BR' elif item.startswith('END'): print 'Found END' elif item.find(':') and item[(item.find(':') -1)].isalpha(): print 'Mya have found a label' else: print 'Not sure what I found'

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• Scala's lazy arguments: How do they work?

  - by python dude

  In the file Parsers.scala (Scala 2.9.1) from the parser combinators library I seem to have come across a lesser known Scala feature called "lazy arguments". Here's an example: def ~ [U](q: => Parser[U]): Parser[~[T, U]] = { lazy val p = q // lazy argument (for(a <- this; b <- p) yield new ~(a,b)).named("~") } Apparently, there's something going on here with the assignment of the call-by-name argument q to the lazy val p. So far I have not been able to work out what this does and why it's useful. Can anyone help?

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• should variable be retained or not? iphone-sdk

  - by psebos

  Hi, in the following piece of code I got from a book. The NSString *pPath which is defined in the class as an instance variable. @interface MainViewController : UIViewController { NSString *pPath; } In the implementation after being set it is being retained. I assume that with the assignment the object is automatically retained (because it is an NSString) and there is no need to additionally retain it. - (void) initPrefsFilePath { NSString *documentsDirectory = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"]; pPath = [documentsDirectory stringByAppendingPathComponent: @"flippingprefs.plist"]; [pPath retain]; }

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• DB Design - Linking to a parent without circular reference issues

  - by zSysop

  Hi all, I'm having trouble coming up with a solution for the following issue. Lets say i have a db that looks something like the following: Issue Table Id | Details | CreateDate | ClosedDate Issue Notes Table Id | ObjectId | Notes | NoteDate Issue Assignment Table Id | ObjectId | AssignedToId| AssignedDate I'd like allow the linking of an issue to another issue. I thought about adding a column to the Issue table called ParentIssueId and that would allow me the ability to link issues, but i foresee circular references occurring within the issue table if i go through with this implementation. Is there a better way to go about doing this, and if so, how? Thanks

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• Help with python list-comprehension

  - by leChuck

  A simplified version of my problem: I have a list comprehension that i use to set bitflags on a two dimensional list so: s = FLAG1 | FLAG2 | FLAG3 [[c.set_state(s) for c in row] for row in self.__map] All set_state does is: self.state |= f This works fine but I have to have this function "set_state" in every cell in __map. Every cell in __map has a .state so what I'm trying to do is something like: [[c.state |= s for c in row] for row in self.map] or map(lambda c: c.state |= s, [c for c in row for row in self.__map]) Except that neither works (Syntax error). Perhaps I'm barking up the wrong tree with map/lamda but I would like to get rid on set_state. And perhaps know why assignment does not work in the list-comprehension

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• SQL Server 2005 Weird varchar Behavior

  - by Tom Tresansky

  This SQL Server 2005 T-SQL code: DECLARE @Test1 varchar; SET @Test1 = 'dog'; DECLARE @Test2 varchar(10); SET @Test2 = 'cat'; SELECT @Test1 AS Result1, @Test2 AS Result2; produces: Result1 = d Result2 = cat I would expect either The assignment SET @Test1 = 'dog'; to fail because there isn't enough room in @Test1 Or the SELECT to return 'dog' in the Result1 column. What is up with @Test1? Could someone please explain this behavior?

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• Multiplying Block Matrices in Numpy

  - by Ada Xu

  Hi Everyone I am python newbie I have to implement lasso L1 regression for a class assignment. This involves solving a quadratic equation involving block matrices. minimize x^t * H * x + f^t * x where x 0 Where H is a 2 X 2 block matrix with each element being a k dimensional matrix and x and f being a 2 X 1 vectors each element being a k dimension vector. I was thinking of using nd arrays. such that np.shape(H) = (2, 2, k, k) np.shape(x) = (2, k) But I figured out that np.dot(X, H) doesn't work here. Is there an easy way to solve this problem? Thanks in advance.

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• Counting vowels in a string using recursion

  - by Daniel Love Jr

  In my python class we are learning about recursion. I understand that it's when a function calls itself, however for this particular assignment I can't figure out how exactly to get my function to call it self to get the desired results. I need to simply count the vowels in the string given to the function. def recVowelCount(s): 'return the number of vowels in s using a recursive computation' vowelcount = 0 vowels = "aEiou".lower() if s[0] in vowels: vowelcount += 1 else: ??? I'm really not sure where to go with this, it's quite frustrating. I came up with this in the end, thanks to some insight from here. def recVowelCount(s): 'return the number of vowels in s using a recursive computation' vowels = "aeiouAEIOU" if s == "": return 0 elif s[0] in vowels: return 1 + recVowelCount(s[1:]) else: return 0 + recVowelCount(s[1:])

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• Implementing a recursive menu system a'la Joomla in CodeIgniter

  - by pettersolberg

  Hi I have some sites powered by Joomla, but with my current assignment I wanted to try something new and created with CodeIgniter a really basic CMS (just to suit my client's needs). Everything works fine except menus - multilevel menus like in Joomla, Drupal etc. with items and subitems... My question is: do you know of any tutorials or texts abut implementing such a structure. I've tried the recursion thinggy with while getting children's IDs move downwards from the parent while searching for the currently displayed item's ID. I've tried also the Drupalish way with having a path parameter enclosing ID's all the way from top to bottom '1/23/123/3'. But all in all it was just too chaotic - code something, try it out. If you have some idea on this topic - thanks in advice.

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• What could possibly cause this error(when declaring an object inside a class) ? //noobie question

  - by M4design

  I'm battling with this assignment :) I've got two classes: Ocean and Grid. When I declare an object of the Grid inside the Ocean: unsigned int sharkCount; Grid grid; The compiler/complainer says: error C2146: syntax error : missing ';' before identifier 'grid' Can you possibly predict what produces this error with the limited info' I provided? It seems that as if the Ocean doesn't like the Grid class. Could this be because of the poor implementation of the grid class. BTW the Grid has a default constructor. Yet the error happens in compiling time!. Thanks. EDIT: They're each in separate header file, and I've included the Grid.h in the Ocean.h.

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• Store address dynamic array in c

  - by user280642

  I'm trying to save the address of a dynamic array index. struct sstor *dlist; struct node *q; q->item = &(dlist->item[(dlist->sz)-1]); // Problem? This is my node struct node { char **item; struct node *next; struct node *prev; }; This is my array struct sstor { int sz; int maxsz; char item[][1024]; }; I'm still new to pointers. The line below gives the error: assignment from incompatible pointer type q->item = &(dlist->item[(dlist->sz)-1]);

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• How to: Display multiple related classes in an ASP.NET GridView ?

  - by kversch

  I would like to display students and their grades with a GridView and LinqToSQL like this: assignment1 assignment2 Student 1 55 89 Student 2 87 56 Student 3 92 34 I found this topic but it doesn't answer my question: http://forums.asp.net/t/1557987.aspx I have a many-to-many relationship between students and assignments called "grades". The grade for the assignment is stored in that table in a "gradeNumber" column. I would also like to specify which assignments should be displayed in the grid. Btw, my LINQ entities are extended to allow me to write/get studentx.Assignments or assignmentx.Students.

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• PHP with SQL Injection

  - by Scott S

  For our first assignment in a System Security class, we have to hack into the professors "cheaply organized" sql database. I know the only user is "admin" and the select statement generated in the php is: select user_id from user where user_username = 'admin' AND user_password = md5('noob') I am having a number of problems attempting to bypass the password part of this statement as the professor has some javascript embedded in the page to sanitize the username and password of any non-alphanumeric values. This can be bypassed by turning off javascript :P but any values sent still get cleaned by the operating system (some build of Debian 32-bit). I've seen the code for the login request and it does not escape any characters. How do I bypass the operating systems escape sequences?

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• Custom Output => List of Errors interpretation in VS2008 IDE.

  - by Hamish Grubijan

  Hello, I have a "database solution" project in VS2008 - it generates SQL for more than one DB vendor from some sort of templates. In order to save time, I also have a tool in VS2008 configured (a Python script), which can compile an individual stored procedure. Now, with the Python script I have the freedom of processing the output and have it take on whatever form I want. I am toying with an idea of having these errors and warnings somehow recognized and populating the click-able Error / Warning list. This is what a typical Oracle error looks like: LINE/COL ERROR -------- ----------------------------------------------------------------- 324/5 PL/SQL: Statement ignored 324/82 PLS-00363: expression 'VSOURCE_SYSTEM_ID' cannot be used as an assignment target Warning: Procedure created with compilation errors. PROCEDURE: ADD_PROPOSED error on creation Errors for PROCEDURE ADD_PROPOSED: LINE/COL ERROR This might be a long shot, but it is worthwhile for me. I do this stuff a lot. Thank you!

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