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  • Is there a "fancy" Ruby way to check whether a local variable is both defined and evaluates to true without using ands and ors?

    - by Steven Xu
    This is quite a quick question. I currently use do_this if (testvar ||= false) Which works just fine. But this approach unnerves me because while fast, it does not short-circuit like defined?(testvar) && testvar does, and it instantiates and assigns a value to a local variable that is subsequently never used, which seems inefficient. I enjoy the very reasonable fact that instance variables are nil before assignment, but I'd like for the situation to be just as easy for local variables.

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  • Passing parameter to base class constructor or using instance variable?

    - by deamon
    All classes derived from a certain base class have to define an attribute called "path". In the sense of duck typing I could rely upon definition in the subclasses: class Base: pass # no "path" variable here def Sub(Base): def __init__(self): self.path = "something/" Another possiblity would be to use the base class constructor: class Base: def __init__(self, path): self.path = path def Sub(Base): def __init__(self): super().__init__("something/") What would you prefer and why? Is there a better way?

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  • C++ include statement required if defining a map in a headerfile.

    - by Justin
    I was doing a project for computer course on programming concepts. This project was to be completed in C++ using Object Oriented designs we learned throughout the course. Anyhow, I have two files symboltable.h and symboltable.cpp. I want to use a map as the data structure so I define it in the private section of the header file. I #include <map> in the cpp file before I #include "symboltable.h". I get several errors from the compiler (MS VS 2008 Pro) when I go to debug/run the program the first of which is: Error 1 error C2146: syntax error : missing ';' before identifier 'table' c:\users\jsmith\documents\visual studio 2008\projects\project2\project2\symboltable.h 22 Project2 To fix this I had to #include <map> in the header file, which to me seems strange. Here are the relevant code files: // symboltable.h #include <map> class SymbolTable { public: SymbolTable() {} void insert(string variable, double value); double lookUp(string variable); void init(); // Added as part of the spec given in the conference area. private: map<string, double> table; // Our container for variables and their values. }; and // symboltable.cpp #include <map> #include <string> #include <iostream> using namespace std; #include "symboltable.h" void SymbolTable::insert(string variable, double value) { table[variable] = value; // Creates a new map entry, if variable name already exist it overwrites last value. } double SymbolTable::lookUp(string variable) { if(table.find(variable) == table.end()) // Search for the variable, find() returns a position, if thats the end then we didnt find it. throw exception("Error: Uninitialized variable"); else return table[variable]; } void SymbolTable::init() { table.clear(); // Clears the map, removes all elements. }

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  • Python parsing error message functions

    - by user1716168
    The code below was created by me with the help of many SO veterans: The code takes an entered math expression and splits it into operators and operands for later use. I have created two functions, the parsing function that splits, and the error function. I am having problems with the error function because it won't display my error messages and I feel the function is being ignored when the code runs. An error should print if an expression such as this is entered: 3//3+4,etc. where there are two operators together, or there are more than two operators in the expression overall, but the error messages dont print. My code is below: def errors(): numExtrapolation,opExtrapolation=parse(expression) if (len(numExtrapolation) == 3) and (len(opExtrapolation) !=2): print("Bad1") if (len(numExtrapolation) ==2) and (len(opExtrapolation) !=1): print("Bad2") def parse(expression): operators= set("*/+-") opExtrapolate= [] numExtrapolate= [] buff=[] for i in expression: if i in operators: numExtrapolate.append(''.join(buff)) buff= [] opExtrapolate.append(i) opExtrapolation=opExtrapolate else: buff.append(i) numExtrapolate.append(''.join(buff)) numExtrapolation=numExtrapolate #just some debugging print statements print(numExtrapolation) print("z:", len(opExtrapolation)) return numExtrapolation, opExtrapolation errors() Any help would be appreciated. Please don't introduce new code that is any more advanced than the code already here. I am looking for a solution to my problem... not large new code segments. Thanks.

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  • In C++, what happens when you return a variable?

    - by wowus
    What happens, step by step, when a variable is returned. I know that if it's a built-in and fits, it's thrown into rax/eax/ax. What happens when it doesn't fit, and/or isn't built-in? More importantly, is there a guaranteed copy constructor call? edit: What about the destructor? Is that called "sometimes", "always", or "never"?

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  • How to store the hostname in a variable in a .bat file?

    - by eqbridges
    I would like to convert this /bin/sh syntax into a widely compatible Windows batch script: host=`hostname` echo ${host} How to do this so that it'll work on any Windows Vista, Windows XP, and Windows 2000 machine? To clarify: I would then like to go on in the program and use the hostname as stored in the variable host. In other words, the larger goal of the program is not to simply echo the hostname.

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  • is it correct to unset the session variable for a particular index as the vay whole session is made

    - by OM The Eternity
    is it correct to unset the session variable for a particular index as the vay whole session is made unset in PHP? I know this works: unset($_SESSION['bannersize']) But does this works ? : unset($_SESSION['bannersize'][3]) or is there any other way to unset any particular desired index of the session and then again rearrange the values inside it to remove the empty index..?

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  • Why does 'url' not work as a variable here?

    - by kryptobs2000
    I originally had the variable cpanel named url and the code would not return anything. Any idea why? It doesn't seem to be used by anything else, but there's gotta be something I'm overlooking. import urllib2 cpanel = 'http://www.tas-tech.com/cpanel' req = urllib2.Request(cpanel) try: handle = urllib2.urlopen(req) except IOError, e: if hasattr(e, 'code'): if e.code != 401: print 'We got another error' print e.code else: print e.headers print e.headers['www-authenticate']

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  • How can I save shell output to a variable in LaTeX?

    - by Frank
    I need to be able to execute a shell command through LaTeX [*] and have the resulting output available for use later on in the form of a LaTeX 'variable' (e.g., via a subsequent \newcommand command). If necessary a temporary file could be used to hold the output, although I would like to avoid this. I have been able to use \immediate\write18 to invoke a bash command before, but this was only used to write to a temporary file. [*] I realise that the -shell-escape flag must be set for this to be allowed

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