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  • Is it inefficient to access a python class member container in a loop statement?

    - by Dave
    Hi there. I'm trying to adopt some best practices to keep my python code efficient. I've heard that accessing a member variable inside of a loop can incur a dictionary lookup for every iteration of the loop, so I cache these in local variables to use inside the loop. My question is about the loop statement itself... if I have the following class: class A(object): def init(self) self.myList = [ 'a','b','c', 'd', 'e' ] Does the following code in a member function incur one, or one-per-loop-iteration (5) dictionary lookups? for letter in self.myList: print letter IE, should I adopt the following pattern, if I am concerned about efficiency... localList = self.myList for letter in localList: print letter or is that actually LESS efficient due to the local variable assign? Note, I am aware that early optimization is a dangerous pitfall if I'm concerned about the overall efficiency of code development. Here I am specifically asking about the efficiency of the code, not the coding. Thanks in advance! D

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  • Rationale of C# iterators design (comparing to C++)

    - by macias
    I found similar topic: http://stackoverflow.com/questions/56347/iterators-in-c-stl-vs-java-is-there-a-conceptual-difference Which basically deals with Java iterator (which is similar to C#) being unable to going backward. So here I would like to focus on limits -- in C++ iterator does not know its limit, you have by yourself compare the given iterator with the limit. In C# iterator knows more -- you can tell without comparing to any external reference, if the iterator is valid or not. I prefer C++ way, because once having iterator you can set any iterator as a limit. In other words if you would like to get only few elements instead of entire collection, you don't have to alter the iterator (in C++). For me it is more "pure" (clear). But of course MS knew this and C++ while designing C#. So what are the advantages of C# way? Which approach is more powerful (which leads to more elegant functions based on iterators). What do I miss? If you have thoughts on C# vs. C++ iterators design other than their limits (boundaries), please also answer. Note: (just in case) please, keep the discussion strictly technical. No C++/C# flamewar.

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  • What's the new way to iterate over a Java Map in Scala 2.8.0?

    - by Alex R
    How does scala.collection.JavaConversions supercede the answers given here: http://stackoverflow.com/questions/495741/iterating-over-java-collections-in-scala (doesn't work because the "jcl" package is gone) and here http://www.eishay.com/2009/05/iterating-over-map-with-scala.html (doesn't work me in a complicated test which I'll try to boil down and post here later) The latter is actually a Scala Map question but I think I need to know both answers in order to iterate over a java.util.Map. Thanks

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  • Can knowing C actually hurt the code you write in higher level languages?

    - by Jurily
    The question seems settled, beaten to death even. Smart people have said smart things on the subject. To be a really good programmer, you need to know C. Or do you? I was enlightened twice this week. The first one made me realize that my assumptions don't go further than my knowledge behind them, and given the complexity of software running on my machine, that's almost non-existent. But what really drove it home was this Slashdot comment: The end result is that I notice the many naive ways in which traditional C "bare metal" programmers assume that higher level languages are implemented. They make bad "optimization" decisions in projects they influence, because they have no idea how a compiler works or how different a good runtime system may be from the naive macro-assembler model they understand. Then it hit me: C is just one more abstraction, like all others. Even the CPU itself is only an abstraction! I've just never seen it break, because I don't have the tools to measure it. I'm confused. Has my mind been mutilated beyond recovery, like Dijkstra said about BASIC? Am I living in a constant state of premature optimization? Is there hope for me, now that I realized I know nothing about anything? Is there anything to know, even? And why is it so fascinating, that everything I've written in the last five years might have been fundamentally wrong? To sum it up: is there any value in knowing more than the API docs tell me? EDIT: Made CW. Of course this also means now you must post examples of the interpreter/runtime optimizing better than we do :)

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  • Where to translate message strings - in the view or in the model?

    - by GrGr
    We have a multilingual (PHP) application and use gettext for i18n. There are a few classes in the backend/model that return messages or message formats for printf(). We use xgettext to extract the strings that we want to translate. We apply the gettext function T_() in the frontend/view - this seems to be where it belongs. So far we kept the backend clean from T_() calls, this way we can also unit-test messages. So in the frontend we have something like echo T_($mymodel->getMessage()); or printf(T_($mymodel->getMessageFormat()), $mymodel->getValue()); This makes it impossible to apply xgettext to extract the strings, unless we put some dummy T_("my message %s to translate") call in the MyModel class. So this leads to the more general question: Do you apply translation in the backend classes, resp. where do you apply translation and how do you keep track of the strings which you have to translate? (I am aware of Question: poedit workaround for dynamic gettext.)

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  • Drawing Directed Acyclic Graphs: Using DAG property to improve layout/edge routing?

    - by Robert Fraser
    Hi, Laying out the verticies in a DAG in a tree form (i.e. verticies with no in-edges on top, verticies dependent only on those on the next level, etc.) is rather simple. However, is there a simple algorithm to do this that minimizes edge crossing? (For some graphs, it may be impossible to completely eliminate edge crossing.) A picture says a thousand words, so is there an algorithm that would suggest: instead of:

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  • Code Golf: Numeric Ranges

    - by SLaks
    Mods: Can you please make this Community Wiki? Challenge Compactify a long list of numbers by replacing consecutive runs with ranges. Example Input 1, 2, 3, 4, 7, 8, 10, 12, 13, 14, 15 Output: 1 - 4, 7, 8, 10, 12 - 15 Note that ranges of two numbers should be left as is. (7, 8; not 7 - 8) Rules You can accept a list of integers (or equivalent datatype) as a method parameter, from the commandline, or from standard in. (pick whichever option results in shorter code) You can output a list of strings by printing them, or by returning either a single string or set of strings. Reference Implementation (C#) IEnumerable<string> Sample(IList<int> input) { for (int i = 0; i < input.Count; ) { var start = input[i]; int size = 1; while (++i < input.Count && input[i] == start + size) size++; if (size == 1) yield return start.ToString(); else if (size == 2) { yield return start.ToString(); yield return (start + 1).ToString(); } else if (size > 2) yield return start + " - " + (start + size - 1); } }

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  • Getting specific values with regex

    - by David
    I need to knowingly isolate each row of the vCard and get its value. For instance, I want to get "5555" from X-CUSTOMFIELD. So far, my thoughts are: "X-CUSTOMFIELD;\d+" I have been looking at some tutorials and I am a little confused with what function to use? What would my regex above return? Would it give me the whole line or just the numerical part (5555)? I was thinking I i get the whole row, I can use substring to get the digits? BEGIN:VCARD VERSION:2.1 N:Last;First; FN:First Last TEL;HOME;VOICE:111111 TEL;MOBILE;VOICE:222222 X-CUSTOMFIELD;5555 END:VCARD

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  • How can I add similar functionality to a number of methods in java?

    - by Roman
    I have a lot of methods for logging, like logSomeAction, logAnotherAction etc. Now I want all these methods make a small pause after printing messages (Thread.sleep). If I do it manually, I would do something like this: //before: public static void logSomeAction () { System.out.println (msg(SOME_ACTION)); } //after: public static void logSomeAction () { System.out.println (msg(SOME_ACTION)); try { Thread.sleep (2000); } catch (InterruptedException ignored) { } } I remember that Java has proxy classes and some other magic-making tools. Is there any way avoid copy-n-pasting N sleep-blocks to N logging methods?

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  • Efficient Multiplication of Varying-Length #s [Conceptual]

    - by Milan Patel
    Write the pseudocode of an algorithm that takes in two arbitrary length numbers (provided as strings), and computes the product of these numbers. Use an efficient procedure for multiplication of large numbers of arbitrary length. Analyze the efficiency of your algorithm. I decided to take the (semi) easy way out and use the Russian Peasant Algorithm. It works like this: a * b = a/2 * 2b if a is even a * b = (a-1)/2 * 2b + a if a is odd My pseudocode is: rpa(x, y){ if x is 1 return y if x is even return rpa(x/2, 2y) if x is odd return rpa((x-1)/2, 2y) + y } I have 3 questions: Is this efficient for arbitrary length numbers? I implemented it in C and tried varying length numbers. The run-time in was near-instant in all cases so it's hard to tell empirically... Can I apply the Master's Theorem to understand the complexity...? a = # subproblems in recursion = 1 (max 1 recursive call across all states) n / b = size of each subproblem = n / 1 - b = 1 (problem doesn't change size...?) f(n^d) = work done outside recursive calls = 1 - d = 0 (the addition when a is odd) a = 1, b^d = 1, a = b^d - complexity is in n^d*log(n) = log(n) this makes sense logically since we are halving the problem at each step, right? What might my professor mean by providing arbitrary length numbers "as strings". Why do that? Many thanks in advance

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  • Is XML-RPC bad used as a protocol for a public API implementation?

    - by Jack Duluoz
    I need to implement a web API for a project I'm working on in this period. I read there are many standard protocols to do it: XML-RPC, SOAP, REST. Apparently, the XML-RPC one is the easiest one to implement and use from what I saw, but I didn't find anything about using it to implement an API. Instead I found many tutorial about creating a REST API in PHP, for example. Is there any counter-indication for using XML-RPC to implement a public web API? Also, more generally speaking, I could (sort of) define a custom protocol for my API, to keep things simpler (i.e. accepting only GET request containing the parameters I need): would this be so bad? Is using a standard protocol a must-do?

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  • Using Closure Properties to prove Regularity

    - by WATWF
    Here's a homework problem: Is L_4 Regular? Let L_4 = L*, where L={0^i1^i | i>=1}. I know L is non-regular and I know that Kleene Star is a closed operation, so my assumption is that L_4 is non-regular. However my professor provided an example of the above in which L = {0^p | p is prime}, which he said was regular by proving that L* was equal to L(000* + e) by saying each was a subset of one another (e in this case means the empty word). So his method involved forming a regex of 0^p, but how I can do that when I essentially have one already?

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  • Should I write my own forum software?

    - by acidzombie24
    I have already built a site from scratch. It has banning, PM, comments, etc. The PMs and comments are done using markdown (like SO). There are pros and cons for writing my own or using another software. But some cons keeping me from using another forum software is Multiple Logins: One for the site, one for separate forums. Need to Customization code: I'll need to change the toolbar in the forum software so I can access pages on the regular site. Look consistency: It may look drastically different from my site even after applying lots of css changes. Banning and User consistency. Users may be ban on site or on forums but not the other. users may select a different or multiple usernames on the forum instead of being forced to use the same username on both site and forum. Should I write my own forum code or should I use something already written? What are some reasons for or against writing my own and using forum software?

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  • Technical non-terminating condition in a loop

    - by Snarfblam
    Most of us know that a loop should not have a non-terminating condition. For example, this C# loop has a non-terminating condition: any even value of i. This is an obvious logic error. void CountByTwosStartingAt(byte i) { // If i is even, it never exceeds 254 for(; i < 255; i += 2) { Console.WriteLine(i); } } Sometimes there are edge cases that are extremely unlikeley, but technically constitute non-exiting conditions (stack overflows and out-of-memory errors aside). Suppose you have a function that counts the number of sequential zeros in a stream: int CountZeros(Stream s) { int total = 0; while(s.ReadByte() == 0) total++; return total; } Now, suppose you feed it this thing: class InfiniteEmptyStream:Stream { // ... Other members ... public override int Read(byte[] buffer, int offset, int count) { Array.Clear(buffer, offset, count); // Output zeros return count; // Never returns -1 (end of stream) } } Or more realistically, maybe a stream that returns data from external hardware, which in certain cases might return lots of zeros (such as a game controller sitting on your desk). Either way we have an infinite loop. This particular non-terminating condition stands out, but sometimes they don't. A completely real-world example as in an app I'm writing. An endless stream of zeros will be deserialized into infinite "empty" objects (until the collection class or GC throws an exception because I've exceeded two billion items). But this would be a completely unexpected circumstance (considering my data source). How important is it to have absolutely no non-terminating conditions? How much does this affect "robustness?" Does it matter if they are only "theoretically" non-terminating (is it okay if an exception represents an implicit terminating condition)? Does it matter whether the app is commercial? If it is publicly distributed? Does it matter if the problematic code is in no way accessible through a public interface/API? Edit: One of the primary concerns I have is unforseen logic errors that can create the non-terminating condition. If, as a rule, you ensure there are no non-terminating conditions, you can identify or handle these logic errors more gracefully, but is it worth it? And when? This is a concern orthogonal to trust.

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  • Data Usage Checker Tools

    - by Lucifer
    Hey All, I am about to begin a project for a new client, and am worried about a few things concerning data usage on their internet plan. We're in an area where most of the major networks don't cover the area, and the ones that do, have very expensive plans, with very low data allowance per month. I need to develop an app, but part of the problem lies with checking database values every 30 seconds. It's pretty important that this check is happening every 30 seconds, as the database is actually updated all day everyday, approx. every 5seconds (apparently). Each row in the database consists of about a page full of text if you were to paste it into MS Word. So, are there any logical ways of minimizing data usage in my case, and also how am I able to see exactly how much data is used just to establish a connection to the database? Are there any tools for this kind of info? Thanks :)

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  • Function for creating color wheels

    - by lbrandy
    This is something I've pseudo-solved many times and never quite found a solution that's stuck with me. The problem is to come up with a way to generate N colors that are as distinguishable as possible where N is a parameter.

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  • Find a regular expression that matches a string?

    - by Mirai
    I need a model for finding all of the regular expressions that would match a particular string. Basically, I need an algorithm for doing what I do to generate a regex search string from some pattern. My purpose for this to create a list of potential regular expressions from a selection of text and order that list from least specific (i.e. string of characters with abitrary length) to most specific (i.e. the string itself) to be used in text editor.

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  • How to check if the given string is palindrome?

    - by Prakash
    Definition: A palindrome is a word, phrase, number or other sequence of units that has the property of reading the same in either direction How to check if the given string is a palindrome? This was one of the FAIQ [Frequently Asked Interview Question] a while ago but that mostly using C. Looking for solutions in any and all languages possible.

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  • Unsigneds in order to prevent negative numbers

    - by Bruno Brant
    let's rope I can make this non-sujective Here's the thing: Sometimes, on fixed-typed languages, I restrict input on methods and functions to positive numbers by using the unsigned types, like unsigned int or unsigned double, etc. Most libraries, however, doesn't seem to think that way. Take C# string.Length. It's a integer, even though it can never be negative. Same goes for C/C++: sqrt input is an int or a double. I know there are reasons for this ... for example your argument might be read from a file and (no idea why) you may prefer to send the value directly to the function and check for errors latter (or use a try-catch block). So, I'm assuming that libraries are way better designed than my own code. So what are the reasons against using unsigned numbers to represent positive numbers? It's because of overflow when we cast then back to signed types?

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  • O(N log N) Complexity - Similar to linear?

    - by gav
    Hey All, So I think I'm going to get buried for asking such a trivial but I'm a little confused about something. I have implemented quicksort in Java and C and I was doing some basic comparissons. The graph came out as two straight lines, with the C being 4ms faster than the Java counterpart over 100,000 random integers. The code for my tests can be found here; android-benchmarks I wasn't sure what an (n log n) line would look like but I didn't think it would be straight. I just wanted to check that this is the expected result and that I shouldn't try to find an error in my code. I stuck the formula into excel and for base 10 it seems to be a straight line with a kink at the start. Is this because the difference between log(n) and log(n+1) increases linearly? Thanks, Gav

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  • Why is forwarding variadic parameters invalid?

    - by awesomeyi
    Consider the variadic function parameter: func foo(bar:Int...) -> () { } Here foo can accept multiple arguments, eg foo(5,4). I am curious about the type of Int... and its supported operations. For example, why is this invalid? func foo2(bar2:Int...) -> () { foo(bar2); } Gives a error: Could not find an overload for '_conversion' that accepts the supplied arguments Why is forwarding variadic parameters invalid? What is the "conversion" the compiler is complaining about?

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