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• Indentation control while developing a small python like language

  - by sap

  Hello, I'm developing a small python like language using flex, byacc (for lexical and parsing) and C++, but i have a few questions regarding scope control. just as python it uses white spaces (or tabs) for indentation, not only that but i want to implement index breaking like for instance if you type "break 2" inside a while loop that's inside another while loop it would not only break from the last one but from the first loop as well (hence the number 2 after break) and so on. example: while 1 while 1 break 2 'hello world'!! #will never reach this. "!!" outputs with a newline end 'hello world again'!! #also will never reach this. again "!!" used for cout end #after break 2 it would jump right here but since I don't have an "anti" tab character to check when a scope ends (like C for example i would just use the '}' char) i was wondering if this method would the the best: I would define a global variable, like "int tabIndex" on my yacc file that i would access in my lex file using extern. then every time i find a tab character on my lex file i would increment that variable by 1. when parsing on my yacc file if i find a "break" keyword i would decrement by the amount typed after it from the tabIndex variable, and when i reach and EOF after compiling and i get a tabIndex != 0 i would output compilation error. now the problem is, whats the best way to see if the indentation got reduced, should i read \b (backspace) chars from lex and then reduce the tabIndex variable (when the user doesn't use break)? another method to achieve this? also just another small question, i want every executable to have its starting point on the function called start() should i hardcode this onto my yacc file? sorry for the long question any help is greatly appreciated. also if someone can provide an yacc file for python would be nice as a guideline (tried looking on Google and had no luck). thanks in advance.

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• php parsing speed optimization

  - by Arnaud

  I would like to add tooltip or generate link according to the element available in the database, for exemple if the html page printed is: to reboot your linux host in single-user mode you can ... I will use explode(" ", $row[page]) and the idea is now to lookup for every single word in the page to find out if they have a related referance in this exemple let's say i've got a table referance an one entry for reboot and one for linux reboot: restart a computeur linux: operating system now my output will look like (replaced < and by @) to @a href="ref/reboot"@reboot@/a@ your @a href="ref/linux"@linux@/a@ host in single-user mode you can ... Instead of have a static list generated when I saved the content, if I add more keyword in the future, then the text will become more interactive. My main concerne and question is how can I create a efficient enough process to do it ? Should I store all the db entry in an array and compare them ? Do an sql query for each word (seems to be crazy) Dump the table in a file and use a very long regex or a "grep -f pattern data" way of doing it? Or or or or I'm sure it must be a better way of doing it, just don't have a clue about it, or maybe this will be far too resource un-friendly and I should avoid doing such things. Cheers!

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• python can't start a new thread

  - by Giorgos Komnino

  I am building a multi threading application. I have setup a threadPool. [ A Queue of size N and N Workers that get data from the queue] When all tasks are done I use tasks.join() where tasks is the queue . The application seems to run smoothly until suddently at some point (after 20 minutes in example) it terminates with the error thread.error: can't start new thread Any ideas? Edit: The threads are daemon Threads and the code is like: while True: t0 = time.time() keyword_statuses = DBSession.query(KeywordStatus).filter(KeywordStatus.status==0).options(joinedload(KeywordStatus.keyword)).with_lockmode("update").limit(100) if keyword_statuses.count() == 0: DBSession.commit() break for kw_status in keyword_statuses: kw_status.status = 1 DBSession.commit() t0 = time.time() w = SWorker(threads_no=32, network_server='http://192.168.1.242:8180/', keywords=keyword_statuses, cities=cities, saver=MySqlRawSave(DBSession), loglevel='debug') w.work() print 'finished' When the daemon threads are killed? When the application finishes or when the work() finishes? Look at the thread pool and the worker (it's from a recipe ) from Queue import Queue from threading import Thread, Event, current_thread import time event = Event() class Worker(Thread): """Thread executing tasks from a given tasks queue""" def __init__(self, tasks): Thread.__init__(self) self.tasks = tasks self.daemon = True self.start() def run(self): '''Start processing tasks from the queue''' while True: event.wait() #time.sleep(0.1) try: func, args, callback = self.tasks.get() except Exception, e: print str(e) return else: if callback is None: func(args) else: callback(func(args)) self.tasks.task_done() class ThreadPool: """Pool of threads consuming tasks from a queue""" def __init__(self, num_threads): self.tasks = Queue(num_threads) for _ in range(num_threads): Worker(self.tasks) def add_task(self, func, args=None, callback=None): ''''Add a task to the queue''' self.tasks.put((func, args, callback)) def wait_completion(self): '''Wait for completion of all the tasks in the queue''' self.tasks.join() def broadcast_block_event(self): '''blocks running threads''' event.clear() def broadcast_unblock_event(self): '''unblocks running threads''' event.set() def get_event(self): '''returns the event object''' return event

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• asp.net mvc Ajax.BeginForm clone.

  - by denis_n

  Hello, I'm using asp.net mvc ajax. The partial view is using Ajax.BeginForm (just an example): <div id="divPlaceholder"> <% using (Ajax.BeginForm(new AjaxOptions { UpdateTargetId = "divPlaceholder" })) { %> ... asp.net mvc controls and validation messages <input type="submit" value="Save" /> <% } %> </div> After update, if validation fails, the html is: <div id="divPlaceholder"> <div id="divPlaceholder"> ...form </div> </div> I don't like that the returned html is inserted, instead it should replace original div. Probably on POST I should not render <div> around form in partial view or render the div without id. What else can I do in this situation? I was thinking that maybe I should write a helper, something like Ajax.DivBeginForm, which will render form inside div on GET and hide the div on POST. Can somebody provide a good advice how to write such helper (Ajax.DivBeginForm)? I'd like it to work with using keyword: <% using (Ajax.DivBeginForm(new AjaxOptions { UpdateTargetId = "myId" })) { ... }%>

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• Reporting Services - can't group by a column called "LanguageId"

  - by marc_s

  Folks, I have a really odd behavior here: I have a SQL Server 2008 Reporting Services report which gets grouped and sorted dynamically. One of the column in my data set which I display is called LanguageId and I was trying to get a grouping going by this LanguageId field. I checked, double-checked and triple-checked the data being returned - it does contain my expected values for LanguageId and everything seems fine and dandy. It just never worked - I didn't get the expected groups, I got things like a specific node actually changing its display value from one ID to another when expanding its subitems, and other really whacky stuff. I discovered that grouping and sorting by LanguageCaption works just fine. It also started working fine after I renamed LanguageId to MyLanguageId. So where on earth is this documented that LanguageId appears to be a system variable / reserved word / keyword of some sort in SQL Server Reporting Services that must be avoided at all costs?? I can't seem to find anything on that topic - even Mr. Google and Mrs. Bing came up empty so far....

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• Need feedback on two member functions of a Table class in C++

  - by George

  int Table::addPlayer(Player player, int position) { deque<Player>::iterator it = playerList.begin()+position; deque<Player>::iterator itStart = playerList.begin()+postion; while(*it != "(empty seat)") { it++; if (it == playerList.end()) { it = playerList.begin(); } if (it == itStart) { cout << "Table full" << endl; return -1; } } //TODO overload Player assignment, << operator *it = player; cout << "Player " << player << " sits at position " << it - playerList.begin() << endl; return it - playerList.begin(); } } int Table::removePlayer(Player player) { deque<Player>::iterator it = playerList.begin(); //TODO Do I need to overload != in Player? while(*it != player) { it++; if (it == playerList.end()) { cout << "Player " << player << " not found" << endl; return -1; } } *it = "(empty seat)"; cout << "Player " << player << " stands up from position " << it - playerList.begin() << endl; return it - playerList.begin(); } Would like some feedback on these two member functions of a Table class for Texas Hold Em Poker simulation. Any information syntax, efficiency or even common practices would be much appreciated.

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• Scala and Java BigDecimal

  - by geejay

  I want to switch from Java to a scripting language for the Math based modules in my app. This is due to the readability, and functional limitations of mathy Java. For e.g, in Java I have this: BigDecimal x = new BigDecimal("1.1"); BigDecimal y = new BigDecimal("1.1"); BigDecimal z = x.multiply(y.exp(new BigDecimal("2")); As you can see, without BigDecimal operator overloading, simple formulas get complicated real quick. With doubles, this looks fine, but I need the precision. I was hoping in Scala I could do this: var x = 1.1; var y = 0.1; print(x + y); And by default I would get decimal-like behaviour, alas Scala doesn't use decimal calculation by default. Then I do this in Scala: var x = BigDecimal(1.1); var y = BigDecimal(0.1); println(x + y); And I still get an imprecise result. Is there something I am not doing right in Scala? Maybe I should use Groovy to maximise readability (it uses decimals by default)?

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• R: manipulating data.frames containing strings and booleans.

  - by Mike Dewar

  Hello. I have a data.frame in R; it's called p. Each element in the data.frame is either True or False. My variable p has, say, m rows and n columns. For every row there is strictly only one TRUE element. It also has column names, which are strings. What I would like to do is the following: For every row in p I see a TRUE I would like to replace with the name of the corresponding column I would then like to collapse the data.frame, which now contains FALSEs and column names, to a single vector, which will have m elements. I would like to do this in an R-thonic manner, so as to continue my enlightenment in R and contribute to a world without for-loops. I can do step 1 using the following for loop: for (i in seq(length(colnames(p)))) { p[p[,i]==TRUE,i]=colnames(p)[i] } but theres's no beauty here and I have totally subscribed to this for-loops-in-R-are-probably-wrong mentality. Maybe wrong is too strong but they're certainly not great. I don't really know how to do step 2. I kind of hoped that the sum of a string and FALSE would return the string but it doesn't. I kind of hoped I could use an OR operator of some kind but can't quite figure that out (Python responds to False or 'bob' with 'bob'). Hence, yet again, I appeal to you beautiful Rstats people for help!

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• C++ Beginner Delete Question

  - by Pooch

  Hi all, This is my first year learning C++ so bear with me. I am attempting to dynamically allocate memory to the heap and then delete the allocated memory. Below is the code that is giving me a hard time: // String.cpp #include "String.h" String::String() {} String::String(char* source) { this->Size = this->GetSize(source); this->CharArray = new char[this->Size + 1]; int i = 0; for (; i < this->Size; i++) this->CharArray[i] = source[i]; this->CharArray[i] = '\0'; } int String::GetSize(const char * source) { int i = 0; for (; source[i] != '\0'; i++); return i; } String::~String() { delete[] this->CharArray; } Here is the error I get when the compiler tries to delete the CharArray: 0xC0000005: Access violation reading location 0xccccccc0. And here is the last call on the stack: msvcr100d.dll!operator delete(void * pUserData) Line 52 + 0x3 bytes C++ I am fairly certain the error exists within this piece of code but will provide you with any other information needed. Oh yeah, using VS 2010 for XP. Thanks for any and all help!

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• What's the best way to resolve this scope problem?

  - by Peter Stewart

  I'm writing a program in python that uses genetic techniques to optimize expressions. Constructing and evaluating the expression tree is the time consumer as it can happen billions of times per run. So I thought I'd learn enough c++ to write it and then incorporate it in python using cython or ctypes. I've done some searching on stackoverflow and learned a lot. This code compiles, but leaves the pointers dangling. I tried 'this_node = new Node(...' . It didn't seem to work. And I'm not at all sure how I'd delete all the references as there would be hundreds. I'd like to use variables that stay in scope, but maybe that's not the c++ way. What is the c++ way? class Node { public: char *cargo; int depth; Node *left; Node *right; } Node make_tree(int depth) { depth--; if(depth <= 0) { Node tthis_node("value",depth,NULL,NULL); return tthis_node; } else { Node this_node("operator" depth, &make_tree(depth), &make_tree(depth)); return this_node; } };

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• Creating a Function in SQL Server with a Phone Number as a parameter and returns a Random Number

  - by Emer

  Hi Guys, I am hoping someone can help me here as google is not being as forthcoming as I would have liked. I am relatively new to SQL Server and so this is the first function I have set myself to do. The outline of the function is that it has a Phone number varchar(15) as a parameter, it checks that this number is a proper number, i.e. it is 8 digits long and contains only numbers. The main character I am trying to avoid is '+'. Good Number = 12345678 Bad Number = +12345678. Once the number is checked I would like to produce a random number for each phone number that is passed in. I have looked at substrings, the like operator, Rand(), left(), Right() in order to search through the number and then produce a random number. I understand that Rand() will produce the same random number unless alterations are done to it but right now it is about actually getting some working code. Any hints on this would be great or even point me towards some more documentation. I have read books online and they haven't helped me, maybe I am not looking in the right places. Here is a snippet of code I was working on the Rand declare @Phone Varchar (15) declare @Counter Varchar (1) declare @NewNumber Varchar(15) set @Phone = '12345678' set @Counter = len(@Phone) while @Counter > 0 begin select case when @Phone like '%[0-9]%' then cast(rand()*100000000 as int) else 'Bad Number' end set @counter = @counter - 1 end return Thanks for the help in advance Emer

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• Why does C++ not allow multiple types in one auto statement?

  - by Walter

  The 2011 C++ standard introduced the new keyword auto, which can be used for defining variables instead of a type, i.e. auto p=make_pair(1,2.5); // pair<int,double> auto i=std::begin(c), end=std::end(c); // decltype(std::begin(c)) In the second line, i and end are of the same type, referred to as auto. The standard does not allow auto i=std::begin(container), e=std::end(container), x=*i; when x would be of different type. My question: why does the standard not allow this last line? It could be allowed by interpreting auto not as representing some to-be-decuded type, but as indicating that the type of any variable declared auto shall be deduced from its assigned value. Is there any good reason for the C++11 standard to not follow this approach? There is actually a use case for this, namely in the initialisation statement of for loops: for(auto i=std::begin(c), end=std::end(c), x=*i; i!=end; ++i, x+=*i) { ... } when the scope of the variables i, end, and x is limited to the for loop. AFAIK, this cannot be achieved in C++ unless those variables have a common type. Is this correct? (ugly tricks of putting all types inside a struct excluded) There may also be use cases in some variadic template applications.

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• Which database I can used and relationship in it ??

  - by mimo-hamad

  My projece make me confused which I didn't find clear things that make me understand the required database and the relationships in it So, would a super one help me to solve it ?!! ;D this is required: 1) Model the data stored in the database (Identify the entities, roles, relationships, constraints, etc.) 2) Write the Oracle commands to create the database, find appropriate data, and populate the database 3) Write five different queries on your database, using the SELECT/FROM/WHERE construct provided in SQL. Your five queries should illustrate several different aspects of database querying, such as: a. Queries over more than one relation (by listing more than one relation in the FROM clause) b. Queries involving aggregate functions, such as SUM, COUNT, and AVG c. Queries involving complicated selects and joins d. Queries involving GROUP BY, HAVING or other similar functions. e. Queries that require the use of the DISTINCT keyword. And this the condition that we need to determine it to solve the required Q's above : 5) It is desired to develop an Internet membership club to buy products at special prices online. To join, new members must be referred by another existing member of the club. The system will keep the following information for each member: The member ID, referring member, birth date, member name, address, phone, mobile, credit card type, number and expiration date. The items are always shipped to the member's address noted in the membership application. The shipping fees will differ for each order.For each item to be requested, the member will select an item from a long list of possible items. For each item in the database, we store an item ID, an item name, description, and list price. The list price will be different from the actual sale price. The available quantity and the back-ordered quantity (the back-ordered quantity is the quantity on-order by the club from its suppliers) is also noted

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• In a class with no virtual methods or superclass, is it safe to assume (address of first member vari

  - by Jeremy Friesner

  Hi all, I made a private API that assumes that the address of the first member-object in the class will be the same as the class's this-pointer... that way the member-object can trivially derive a pointer to the object that it is a member of, without having to store a pointer explicitly. Given that I am willing to make sure that the container class won't inherit from any superclass, won't have any virtual methods, and that the member-object that does this trick will be the first member object declared, will that assumption hold valid for any C++ compiler, or do I need to use the offsetof() operator (or similar) to guarantee correctness? To put it another way, the code below does what I expect under g++, but will it work everywhere? class MyContainer { public: MyContainer() {} ~MyContainer() {} // non-virtual dtor private: class MyContained { public: MyContained() {} ~MyContained() {} // Given that the only place Contained objects are declared is m_contained // (below), will this work as expected on any C++ compiler? MyContainer * GetPointerToMyContainer() { return reinterpret_cast<MyContainer *>(this); } }; MyContained m_contained; // MUST BE FIRST MEMBER ITEM DECLARED IN MyContainer int m_foo; // other member items may be declared after m_contained float m_bar; };

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• invasive vs non-invasive ref-counted pointers in C++

  - by anon

  For the past few years, I've generally accepted that if I am going to use ref-counted smart pointers invasive smart pointers is the way to go -- However, I'm starting to like non-invasive smart pointers due to the following: I only use smart pointers (so no Foo* lying around, only Ptr) I'm starting to build custom allocators for each class. (So Foo would overload operator new). Now, if Foo has a list of all Ptr (as it easily can with non-invasive smart pointers). Then, I can avoid memory fragmentation issues since class Foo move the objects around (and just update the corresponding Ptr). The only reason why this Foo moving objects around in non-invasive smart pointers being easier than invasive smart pointers is: In non-invasive smart pointers, there is only one pointer that points to each Foo. In invasive smart pointers, I have no idea how many objects point to each Foo. Now, the only cost of non-invasive smart pointers ... is the double indirection. [Perhaps this screws up the caches]. Does anyone have a good study of expensive this extra layer of indirection is?

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• Syntactical analysis with Flex/Bison part 2

  - by Imran

  Hallo, I need help in Lex/Yacc Programming. I wrote a compiler for a syntactical analysis for inputs of many statements. Now i have a special problem. In case of an Input the compiler gives the right output, which statement is uses, constant operator or a jmp instructor to which label, now i have to write so, if now a if statement comes, first the first command (before the else) must be give out when the assignment of the if is yes then it must jump to the end because the command after the else isnt needed, so after this jmp then the second command must be give out. I show it in an example maybe you understand what i mean. Input adr. Output if(x==0) 10 if(x==0) Wait 5 20 WAIT 5 else 30 JMP 50 Wait 1 40 WAIT 1 end 50 END like so. I have an idea, maybe i can do it whith a special if statement like IF exp jmp_stmt_end stmt_seq END when the if statement is given in the input the compiler has to recognize the end ofthe statement and like my jmp_stmt in my compiler ( you have to download the files from http://bitbucket.org/matrix/changed-tiny) only to jump to the end. I hope you understand my problem.thanks.

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• Few Basic Questions in Overriding

  - by Dahlia

  I have few problems with my basic and would be thankful if someone can clear this. What does it mean when I say base *b = new derived; Why would one go for this? We very well separately can create objects for class base and class derived and then call the functions accordingly. I know that this base *b = new derived; is called as Object Slicing but why and when would one go for this? I know why it is not advisable to convert the base class object to derived class object (because base class is not aware of the derived class members and methods). I even read in other StackOverflow threads that if this is gonna be the case then we have to change/re-visit our design. I understand all that, however, I am just curious, Is there any way to do this? class base { public: void f(){cout << "In Base";} }; class derived:public base { public: void f(){cout << "In Derived";} }; int _tmain(int argc, _TCHAR* argv[]) { base b1, b2; derived d1, d2; b2 = d1; d2 = reinterpret_cast<derived*>(b1); //gives error C2440 b1.f(); // Prints In Base d1.f(); // Prints In Derived b2.f(); // Prints In Base d1.base::f(); //Prints In Base d2.f(); getch(); return 0; } In case of my above example, is there any way I could call the base class f() using derived class object? I used d1.base()::f() I just want to know if there any way without using scope resolution operator? Thanks a lot for your time in helping me out!

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• How to produce 64 bit masks?

  - by egiakoum1984

  Based on the following simple program the bitwise left shit operator works only for 32 bits. Is it true? #include <iostream> #include <stdlib.h> using namespace std; int main(void) { long long currentTrafficTypeValueDec; int input; cout << "Enter input:" << endl; cin >> input; currentTrafficTypeValueDec = 1 << (input - 1); cout << currentTrafficTypeValueDec << endl; cout << (1 << (input - 1)) << endl; return 0; } The output of the program: Enter input: 30 536870912 536870912 Enter input: 62 536870912 536870912 How could I produce 64-bit masks?

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• Reading Unicode files line by line C++

  - by Roger Nelson

  What is the correct way to read Unicode files line by line in C++? I am trying to read a file saved as Unicode (LE) by Windows Notepad. Suppose the file contains simply the characters A and B on separate lines. In reading the file byte by byte, I see the following byte sequence (hex) : FE FF 41 00 0D 00 0A 00 42 00 0D 00 0A 00 So 2 byte BOM, 2 byte 'A', 2byte CR , 2byte LF, 2 byte 'B', 2 byte CR, 2 byte LF . I tried reading the text file using the following code: std::wifstream file("test.txt"); file.seekg(2); // skip BOM std::wstring A_line; std::wstring B_line; getline(file,A_line); // I get "A" getline(file,B_line); // I get "\0B" I get the same results using operator instead of getline file >> A_line; file >> B_line; It appears that the single byte CR character is is being consumed only as the single byte. or CR NULL LF is being consumed but not the high byte NULL. I would expect wifstream in text mode would read the 2byte CR and 2byte LF. What am I doing wrong? It does not seem right that one should have to read a text file byte by byte in binary mode just to parse the new lines.

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• Function with parameter type that has a copy-constructor with non-const ref chosen?

  - by Johannes Schaub - litb

  Some time ago I was confused by the following behavior of some code when I wanted to write a is_callable<F, Args...> trait. Overload resolution won't call functions accepting arguments by non-const ref, right? Why doesn't it reject in the following because the constructor wants a Test&? I expected it to take f(int)! struct Test { Test() { } // I want Test not be copyable from rvalues! Test(Test&) { } // But it's convertible to int operator int() { return 0; } }; void f(int) { } void f(Test) { } struct WorksFine { }; struct Slurper { Slurper(WorksFine&) { } }; struct Eater { Eater(WorksFine) { } }; void g(Slurper) { } void g(Eater) { } // chooses this, as expected int main() { // Error, why? f(Test()); // But this works, why? g(WorksFine()); } Error message is m.cpp: In function 'int main()': m.cpp:33:11: error: no matching function for call to 'Test::Test(Test)' m.cpp:5:3: note: candidates are: Test::Test(Test&) m.cpp:2:3: note: Test::Test() m.cpp:33:11: error: initializing argument 1 of 'void f(Test)' Can you please explain why one works but the other doesn't?

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• Counting entries in a list of dictionaries: for loop vs. list comprehension with map(itemgetter)

  - by Dennis Williamson

  In a Python program I'm writing I've compared using a for loop and increment variables versus list comprehension with map(itemgetter) and len() when counting entries in dictionaries which are in a list. It takes the same time using a each method. Am I doing something wrong or is there a better approach? Here is a greatly simplified and shortened data structure: list = [ {'key1': True, 'dontcare': False, 'ignoreme': False, 'key2': True, 'filenotfound': 'biscuits and gravy'}, {'key1': False, 'dontcare': False, 'ignoreme': False, 'key2': True, 'filenotfound': 'peaches and cream'}, {'key1': True, 'dontcare': False, 'ignoreme': False, 'key2': False, 'filenotfound': 'Abbott and Costello'}, {'key1': False, 'dontcare': False, 'ignoreme': True, 'key2': False, 'filenotfound': 'over and under'}, {'key1': True, 'dontcare': True, 'ignoreme': False, 'key2': True, 'filenotfound': 'Scotch and... well... neat, thanks'} ] Here is the for loop version: #!/usr/bin/env python # Python 2.6 # count the entries where key1 is True # keep a separate count for the subset that also have key2 True key1 = key2 = 0 for dictionary in list: if dictionary["key1"]: key1 += 1 if dictionary["key2"]: key2 += 1 print "Counts: key1: " + str(key1) + ", subset key2: " + str(key2) Output for the data above: Counts: key1: 3, subset key2: 2 Here is the other, perhaps more Pythonic, version: #!/usr/bin/env python # Python 2.6 # count the entries where key1 is True # keep a separate count for the subset that also have key2 True from operator import itemgetter KEY1 = 0 KEY2 = 1 getentries = itemgetter("key1", "key2") entries = map(getentries, list) key1 = len([x for x in entries if x[KEY1]]) key2 = len([x for x in entries if x[KEY1] and x[KEY2]]) print "Counts: key1: " + str(key1) + ", subset key2: " + str(key2) Output for the data above (same as before): Counts: key1: 3, subset key2: 2 I'm a tiny bit surprised these take the same amount of time. I wonder if there's something faster. I'm sure I'm overlooking something simple. One alternative I've considered is loading the data into a database and doing SQL queries, but the data doesn't need to persist and I'd have to profile the overhead of the data transfer, etc., and a database may not always be available. I have no control over the original form of the data. The code above is not going for style points.

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• Concise C# code for gathering several properties with a non-null value into a collection?

  - by stakx

  A fairly basic problem for a change. Given a class such as this: public class X { public T A; public T B; public T C; ... // (other fields, properties, and methods are not of interest here) } I am looking for a concise way to code a method that will return all A, B, C, ... that are not null in an enumerable collection. (Assume that declaring these fields as an array is not an option.) public IEnumerable<T> GetAllNonNullAs(this X x) { // ? } The obvious implementation of this method would be: public IEnumerable<T> GetAllNonNullAs(this X x) { var resultSet = new List<T>(); if (x.A != null) resultSet.Add(x.A); if (x.B != null) resultSet.Add(x.B); if (x.C != null) resultSet.Add(x.C); ... return resultSet; } What's bothering me here in particular is that the code looks verbose and repetitive, and that I don't know the initial List capacity in advance. It's my hope that there is a more clever way, probably something involving the ?? operator? Any ideas?

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• looking to streamline my RSS feed mashup

  - by Mark Cejas

  Hello crafty developers, I have aggregated RSS feeds from various sources with RSSowl, fetching directly from the social mention API. The RSS feeds are categorized into the following major categories: blogs, news, twitter, Q&A and social networking sites. Each major category is nested with a common group of RSS feeds that represent a particular client/brand ontology. Merging these feeds into the RSSowl reader application, allows me to conduct and save refined search queries (from the aggregated data) into a single file - that I can then tag and further segment for analysis. This scheme is utilized for my own research needs and has helped me considerably. However, I find this RSS mashup scheme kinda clumsy, it requires quite a bit of time to initially organize all of the feeds and I would like to be able to do further natural language processing to the data as well as eventually be able to rank the collected list of URL's into some order of media prominence - right I don't want to pay the ridiculous radian6 web analytics fees, when my intuition is telling me that with a bit of 'elbow grease' I can maybe leverage some available resources online to develop a functional low scale web mining application and get some good intelligence from it. I am now starting to learn a little about computer science - my background is in physical science/statistics so is my thinking in the right track? So, I guess I am imagining an application that allows me to query in a refined manner. A manner that allows me to search for keyword combinations, applying AND/OR operators, selectively focus my queries into particular sources - like a collection of blogs or twitter, or social networking communities, then save the results of my queries into a structured format that can then be manipulated and explored. Am I dreaming? I just had to get all of this out. any bit of advice and insight would be hugely appreciated. my best, Mark

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• Am I mocking this helper function right in my Django test?

  - by CppLearner

  lib.py from django.core.urlresolvers import reverse def render_reverse(f, kwargs): """ kwargs is a dictionary, usually of the form {'args': [cbid]} """ return reverse(f, **kwargs) tests.py from lib import render_reverse, print_ls class LibTest(unittest.TestCase): def test_render_reverse_is_correct(self): #with patch('webclient.apps.codebundles.lib.reverse') as mock_reverse: with patch('django.core.urlresolvers.reverse') as mock_reverse: from lib import render_reverse mock_f = MagicMock(name='f', return_value='dummy_views') mock_kwargs = MagicMock(name='kwargs',return_value={'args':['123']}) mock_reverse.return_value = '/natrium/cb/details/123' response = render_reverse(mock_f(), mock_kwargs()) self.assertTrue('/natrium/cb/details/' in response) But instead, I get File "/var/lib/graphyte-webclient/graphyte-webenv/lib/python2.6/site-packages/django/core/urlresolvers.py", line 296, in reverse "arguments '%s' not found." % (lookup_view_s, args, kwargs)) NoReverseMatch: Reverse for 'dummy_readfile' with arguments '('123',)' and keyword arguments '{}' not found. Why is it calling reverse instead of my mock_reverse (it is looking up my urls.py!!) The author of Mock library Michael Foord did a video cast here (around 9:17), and in the example he passed the mock object request to the view function index. Furthermore, he patched POll and assigned an expected return value. Isn't that what I am doing here? I patched reverse? Thanks.

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• SQL - Updating records based on most recent date

  - by Remnant

  I am having difficulty updating records within a database based on the most recent date and am looking for some guidance. By the way, I am new to SQL. As background, I have a windows forms application with SQL Express and am using ADO.NET to interact with the database. The application is designed to enable the user to track employee attendance on various courses that must be attended on a periodic basis (e.g. every 6 months, every year etc.). For example, they can pull back data to see the last time employees attended a given course and also update attendance dates if an employee has recently completed a course. I have three data tables: EmployeeDetailsTable - simple list of employees names, email address etc., each with unique ID CourseDetailsTable - simple list of courses, each with unique ID (e.g. 1, 2, 3 etc.) AttendanceRecordsTable - has 3 columns { EmployeeID, CourseID, AttendanceDate, Comments } For any given course, an employee will have an attendance history i.e. if the course needs to be attended each year then they will have one record for as many years as they have been at the company. What I want to be able to do is to update the 'Comments' field for a given employee and given course based on the most recent attendance date. What is the 'correct' SQL syntax for this? I have tried many things (like below) but cannot get it to work: UPDATE AttendanceRecordsTable SET Comments = @Comments WHERE AttendanceRecordsTable.EmployeeID = (SELECT EmployeeDetailsTable.EmployeeID FROM EmployeeDetailsTable WHERE (EmployeeDetailsTable.LastName =@ParameterLastName AND EmployeeDetailsTable.FirstName =@ParameterFirstName) AND AttendanceRecordsTable.CourseID = (SELECT CourseDetailsTable.CourseID FROM CourseDetailsTable WHERE CourseDetailsTable.CourseName =@CourseName)) GROUP BY MAX(AttendanceRecordsTable.LastDate) After much googling, I discovered that MAX is an aggregate function and so I need to use GROUP BY. I have also tried using the HAVING keyword but without success. Can anybody point me in the right direction? What is the 'conventional' syntax to update a database record based on the most recent date?

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