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• Do Managers in Python Multiprocessing module lock the shared data?

  - by AnonProcess

  This Question has been asked before: http://stackoverflow.com/questions/2936626/how-to-share-a-dictionary-between-multiple-processes-in-python-without-locking However I have several doubts regarding the program given in the answer: The issue is that the following step isn't atomic d['blah'] += 1 Even with locking the answer provided in that question would lead to random results. Since Process 1 read value of d['blah'] saves it on the stack increments it and again writes it. In Between a Process 2 can read the d['blah'] as well. Locking means that while d['blah'] is being written or read no other process can access it. Can someone clarify my doubts?

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• question about missing element in array

  - by davit-datuashvili

  i have following problem from book introduction algorithm second edition by MIT university problem is following An array A[1 . . n] contains all the integers from 0 to n except one. It would be easy to determine the missing integer in O(n) time by using an auxiliary array B[0 . . n] to record which numbers appear in A. In this problem, however, we cannot access an entire integer in A with a single operation. The elements of A are represented in binary, and the only operation we can use to access them is “fetch the j th bit of A[i],” which takes constant time. Show that if we use only this operation, we can still determine the missing inte- ger in O(n) time please help

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• How do I convert a single char in string to an int

  - by Guest

  Keep in mind, if you choose to answer the question, I am a beginner in the field of programming and may need a bit more explanation than others as to how the solutions work. Thank you for your help. My problem is that I am trying to do computations with parts of a string (consisting only of numbers), but I do not know how to convert an individual char to an int. The string is named "message". for (int place = 0; place < message.size(); place++) { if (secondPlace == 0) { cout << (message[place]) * 100 << endl; } } Thank you.

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• Pre Project Documentation

  - by DeanMc

  I have an issue that I feel many programmers can relate to... I have worked on many small scale projects. After my initial paper brain storm I tend to start coding. What I come up with is usually a rough working model of the actual application. I design in a disconnected fashion so I am talking about underlying code libraries, user interfaces are the last thing as the library usually dictates what is needed in the UI. As my projects get bigger I worry that so should my "spec" or design document. The above paragraph, from my investigations, is echoed all across the internet in one fashion or another. When a UI is concerned there is a bit more information but it is UI specific and does not relate to code libraries. What I am beginning to realise is that maybe code is code is code. It seems from my extensive research that there is no 1:1 mapping between a design document and the code. When I need to research a topic I dump information into OneNote and from there I prioritise features into versions and then into related chunks so that development runs in a fairly linear fashion, my tasks tend to look like so: Implement Binary File Reader Implement Binary File Writer Create Object to encapsulate Data for expression to the caller Now any programmer worth his salt is aware that between those three to do items could be a potential wall of code that could expand out to multiple files. I have tried to map the complete code process for each task but I simply don't think it can be done effectively. By the time one mangles pseudo code it is essentially code anyway so the time investment is negated. So my question is this: Am I right in assuming that the best documentation is the code itself. We are all in agreement that a high level overview is needed. How high should this be? Do you design to statement, class or concept level? What works for you?

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• Additional information with widgets in django

  - by fromclouds

  I am displaying a django widget, with which I need to display additional information (something like a tool tip) that is attendant to the widget. I essentially have a widget that asks a random question, which is self contained. {{ form.fieldname }} displays the full widget which looks something like (à la the widget's render method): <label for="id_answer">Question:</label> <input type="hidden" name="question_id" value="n" /> <span class="prompt">What is the air-speed velocity of an unladen swallow?</span> <input type="text" name="answer" /> What I'm essentially asking is, is there a way to break out the prompt, so that I can lay the widget out piecemeal? I would like to lay it out not with a call to {{ form.fieldname }} as above, but like: {{ form.fieldname.label }} {{ form.fieldname.prompt }} {{ form.fieldname }} Does anyone know how to do this?

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• help regarding PERL program

  - by riya

  Could someone write simple PERL programs for the following scenarios: 1) convert a list from {1,2,3,4,5,7,9,10,11,12,34} to {1-5,7,9-12,34} 2) to sort a list of negative numbers 3) to insert values to hash array 4) there is a file with content: C1 c2 c3 c4 r1 r2 r3 r4 put it into an hash array where keys = {c1,c2,c3,c4} and values = {r1,r2,r3,r4} 5) There are testcases running each testcase runs as a process and has a process ID. The logs are logged in a logfile process ID appended to each line. Prog to find out if the test case has passed or failed. The program shoud be running till the processes are running and display output.

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• General question: Filesystem or database?

  - by poeschlorn

  Hey guys, i want to create a small document management system. there are several users who store their files. each file which is uploaded contains an info which user uploaded it and the document content itself. In a view there are displayed all files of ONE specific user, ordered by date. What would be better: 1) giving the documents a name or metadata(XML) which contain the date and user (and iterate through them to get the metadata) or 2) giving the files a random/unique name and store metadata in a DB? something like this: date | user | filename What would you say and why? The used programming language is java and the DB is MySQL.

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• Merging contents of two lists based on a if-loop

  - by chavanak

  I have a minor problem while checking for elements in a list: I have two files with contents something like this file 1: file2: 47 358 47 48 450 49 49 56 50 I parsed both files into two lists and used the following code to check for i in file_1: for j in file_2: j = j.split() if i == j[1]: x=' '.join(j) I am now trying to get a "0" if the value of file_1 is not there in file_2 for example, value "48" is not there is file_2 so I need to get the output like (with only one space in between the two numbers): output_file: 358 47 0 48 450 49 56 50 I tried using the dictionary approach but I didn't quite get what I wanted (actually I don't know how to use dictionary in python correctly ;)). Any help will be great.

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• Remove special chars from URL

  - by John Jones

  Hi, I have a product database and I am displaying trying to display them as clean URLs, below is example product names: PAUL MITCHELL FOAMING POMADE (150ml) American Crew Classic Gents Pomade 85g Tigi Catwalk Texturizing Pomade 50ml What I need to do is display like below in the URL structrue: www.example.com/products/paul-mitchell-foaming-gel(150ml) The problem I have is I want to do the following: Remove anything with braquets(and the braquets) Remove any numbers next to g or ml e.g. 400ml, 10g etc... I have been banging my head trying different string replaces but cant get it right, I would really appreciate some help. Cheers

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• Create dynamic view with android

  - by ekevin

  Hi I'm stuck on a problem and if possible I will need help from the community. I'm not looking for a ready-made solution, but something which would help me to produce the result. I'm looking for a way to produce a dynamic activity based on a JSON object. Here an example of a JSON object: [ { "name": "my checkbox name", "type": "checkbox", "value": "one,two,three" } { "name": "my edit text", "type": "text", "value": "" } ...] This JSONObject could be totally random. I could have 2 text views, 3 select menus, 1 text view and so on. The goal is to iterate over this JSONObject and create the appropriate elements within my android code. To produce the result I've thought of a simple switch which would render one by one my different JSONObject to an android widget. But after that how could I have access of every property of every widget rendered? Thank you.

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• How can I make hundreds of simultaneously running processes communicate with a database through one

  - by Olfan

  Long speech short: How can I make hundreds of simultaneously running processes communicate with a database through one or few permanent sessions? The whole story: I once built a number crunching engine that handles vast amounts of large data files by forking off one child after another giving each a small number of files to work on. File locking, progress monitoring and result propagation happen in an Oracle database which all (sub-)processes access at various times using an application-specific module which encapsulates DBI. This worked well at first, but now with higher volumes of input data, the number of database sessions (one per child, and they can be very short-lived) constantly being opened and closed is becoming an issue. I now want to centralise database access so that there are only one or few fixed database sessions which handle all database access for all the (sub-)processes. The presence of the database abstraction module should make the changes easy because the function calls in the worker instances can stay the same. My problem is that I cannot think of a suitable way to enhance said module in order to establish communication between all the processes and the database connector(s). I thought of message queueing, but couldn't come up with a way of connecting a large herd of requestors with one or few database connectors in a way so that bidirectional communication is possible (for collecting the query result). An asynchronous approach could help here in that all requests are written to the same queue and the database connector servicing the request will "call back" to submit the result. But my mind fails me in generating an image clear enough so that I can paint into code. Threading instead of forking might have given me an easier start, but this would now require massive changes to the code base that I'm not prepared to do to a live system. The more I think of it, the more the base idea looks like a pre-forked web server to me only that it doesn't serve web pages but database queries. Any ideas on what to dig into, and where? Sample (pseudo) code to inspire me, links to possibly related articles, ready solutions on CPAN maybe?

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• Building a linked list with LINQ

  - by FreshCode

  What is the fastest way to order an unordered list of elements by predecessor (or parent) element index using LINQ? Each element has a unique ID and the ID of that element's predecessor (or parent) element, from which a linked list can be built to represent an ordered state. Example ID | Predecessor's ID --------|-------------------- 20 | 81 81 | NULL 65 | 12 12 | 20 120 | 65 The sorted order is {81, 20, 12, 65, 120}. An (ordered) linked list can easily be assembled iteratively from these elements, but can it be done in fewer LINQ statements? Edit: I should have specified that IDs are not necessarily sequential. I chose 1 to 5 for simplicity. See updated element indices which are random.

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• Masking a bit in C returning unexpected result

  - by Eamorr

  0x7F000000 is 0111 1111 0000 0000 0000 0000 0000 0000 in 32 bit binary. 0x01000058 is 0000 0001 0000 0000 0000 0000 0101 1000. When I AND the two numbers together I expect 0000 0001 0000 0000 0000 0000 0000 0000, but for some reason I get 0. Here is my code: #define MASK_binop 0x80000000 #define MASK_operation 0x7F000000 int instruction=atoi(line); if((MASK_binop & instruction)>0) printf("binop\n"); else if((MASK_operation & instruction)>0) printf("operation\n"); Each of the above comparisons keeps returning zero. Is it something to do with 32/64 bits? I'm using 64-bit compiler.

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• Does breaking chained Select()s in LINQ to objects hurt performance?

  - by Justin

  Take the following pseudo C# code: using System; using System.Data; using System.Linq; using System.Collections.Generic; public IEnumerable<IDataRecord> GetRecords(string sql) { // DB logic goes here } public IEnumerable<IEmployer> Employers() { string sql = "select EmployerID from employer"; var ids = GetRecords(sql).Select(record => (record["EmployerID"] as int?) ?? 0); return ids.Select(employerID => new Employer(employerID) as IEmployer); } Would it be faster if the two Select() calls were combined? Is there an extra iteration in the code above? Is the following code faster? public IEnumerable<IEmployer> Employers() { string sql = "select EmployerID from employer"; return Query.Records(sql).Select(record => new Employer((record["EmployerID"] as int?) ?? 0) as IEmployer); } I think the first example is more readable if there is no difference in performance.

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• Creating a Skill Calculator for Runescape

  - by USDblades

  I am beginning C++. I have a long way to go and I am one to never stop learning. I want to create a project for myself that will allow me to learn as I go. It will also give me the motivation and possibly add to my portfolio when I graduate. The runescape skill calculator will ask for your current experience in the current skill of your choosing and your desired level. For Example: my woodcutting experience is 60 and I want to get to lvl 5 which is 120 exp. That means im 60 experience away. by cutting oak logs I get 5 experience per log. The calculator would tell me I need to cut 12 Oak logs. All these numbers are made up. So to my question. Where would I even begin? Hoping it would have buttons to press.

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• How to implement a grapher in C#

  - by iansinke

  So I'm writing a graphing calculator. So far I have a semi-functional grapher, however, I'm having a hard time getting a good balance between accurate graphs and smooth looking curves. The current implementation (semi-pseudo-code) looks something like this: for (float i = GraphXMin; i <= GraphXMax; i++) { PointF P = new PointF(i, EvaluateFunction(Function, i) ListOfPoints.Add(P) } Graphics.DrawCurve(ListOfPoints) The problem with this is since it only adds a point at every integer value, graphs end up distorted when their turning points don't fall on integers (e.g. sin(x)^2). I tried incrementing i by something smaller (like 0.1), which works, but the graph looks very rough. I am using C# and GDI+. I have SmoothingMethod set to AntiAlias, so that's not the problem, as you can see from the first graph. Is there some sort of issue with drawing curves with a lot of points? Should the points perhaps be positioned exactly on pixels? I'm sure some of you have worked on something very similar before, so any suggestions? While you're at it, do you have any suggestions for graphing functions with asymptotes? e.g. 1/x^2 P.S. I'm not looking for a library that does all this - I want to write it myself.

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• Sorting in Matlab

  - by smichak

  Hi, I would like to sort elements in a comma-separated list. The elements in the list are structs and I would like the list to be sorted according to one of the fields in the struct. For example, given the following code: L = {struct('obs', [1 2 3 4], 'n', 4), struct('obs', [6 7 5 3], 'n', 2)}; I would want to have a way to sort L by the field 'n'. Matlab's sort function only works on matrices or arrays and on lists of strings (not even lists of numbers). Any ideas on how that may be achieved? Thanks, Micha

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• Charaters with jquery json

  - by Mikk

  Hi everyone, I'm using jquery $.getJSON to retrieve list of cities. Everything works fine, but I'm from Estonia (probably most of you don't know much about this country =D) and we are using some characters like õ, ü. ä, ö. When I pass letters like this to callback function, I keep getting empty strings. I've tried to base64 encode(server-side)-decode(jquery base64 plugin) strings (i thought it was a good idea as long as I can compress pages with php, so I don't have to worry about bandwidth), but in this way I end up with some random chinese symbols. What would be the best workaround for this problem. Thank you.

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• how to control textbox type to double in visual basic?

  - by fema

  Hi, I'd like to make a textbox that accepts only numbers, but not integer, but rather double. I've read here about e.Handled = Not Char.IsDigit(e.KeyChar) and it works, but again, it can be used only for integer, since it declines decimal point. Another thing I've read here is If Not Double.TryParse(TextBox2.Text, value) Then .... and it would work fine, except that it allows only decimal comma instead of point. I don't know whether it's because of my location settings (Hungary, we use commas instead of points), but I don't have any other idea how to solve my problem, and the SQL server I send my data uses decimal point. Thanks in advance.

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• Balanced Search Tree Query, Asymtotic Analysis..

  - by AGeek

  Hi, The situation is as follows:- We have n number and we have print them in sorted order. We have access to balanced dictionary data structure, which supports the operations serach, insert, delete, minimum, maximum each in O(log n) time. We want to retrieve the numbers in sorted order in O(n log n) time using only the insert and in-order traversal. The answer to this is:- Sort() initialize(t) while(not EOF) read(x) insert(x,t); Traverse(t); Now the query is if we read the elements in time "n" and then traverse the elements in "log n"(in-order traversal) time,, then the total time for this algorithm (n+logn)time, according to me.. Please explain the follow up of this algorithm for the time calculation.. How it will sort the list in O(nlogn) time?? Thanks.

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• Java Swing - Problem in JSpinner

  - by Yatendra Goel

  I am developing a Java Desktop Application and designing the GUI with the help of Netbeans Swing GUI builder. I want to use a JSpinner in my app. I have dragged and dropped it to a JPanel. Now, I want to set its two properties: First, It should display numbers in the range of 1 to 50. Neither less than 1 nor greater than 50. How can I set that range? Second, when I try to get the value of it by spinner.getValue() it returns an Object. As my spinner's data type is Integer, would it be better to downcast the Object into Integer or Is there any other way to get that numeric value?

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• Parsing a string representing a float *with an exponent* in Python

  - by Lucas

  Hi, I have a large file with numbers in the form of 6,52353753563E-7. So there's an exponent in that string. float() dies on this. While I could write custom code to pre-process the string into something float() can eat, I'm looking for the pythonic way of converting these into a float (something like a format string passed somewhere). I must say I'm surprised float() can't handle strings with such an exponent, this is pretty common stuff. I'm using python 2.6, but 3.1 is an option if need be.

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• R - Subsetting XTS via Time and Which

  - by user2844947

  Currently, I have a XTS, called Data, which contains a Date, and two value columns which are numbers. I would like to get a single number as output and which would be the mean of Value1 in the time period from a point where Value2 < mean(Value2) and going forward 14 data points, weeks in this particular data set. In order to get the dates where Value2 < mean(Value2), I wrote the below code Data[which(Data$Value2 < mean(Data$Value2)),"Date"] However, I am not sure how to get the mean of Value1 in the period, going 14 days forward from each of the resultant dates from the above code.

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• infix formula in the input

  - by gcc

  input: sqrt(2 - sin(3*A/B)^2.5) + 0.5*(C*~(D) + 3.11 +B) a b /*there are values for a,b,c,d */ c d input : sqrt(2 - asin(3*A/B)^2.5) +cos(0.5*(C*~(D)) + 3.11 +B) a b /*there are values for a,b,c,d */ c d input: sqrt(2 - sin(3*A/B)^2.5)/(0.5*(C*~(D)) + sin(3.11) +ln(B)) /*max lenght of formula is 250 characters*/ a b /*there are values for a,b,c,d */ c /*each variable with set of floating numbers*/ d As you can see infix formula in the input depends on user. My program will take a formula and n-tuples value. Then it calculate the results for each value of a,b,c and d. If you wonder I am saying ;outcome of program is graph. I dont know way how to store the formula so that I can do my job with easy. can you show me? a,b,c,d is letters cos,sin,sqrt,ln is function

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• Floating point Endianness?

  - by cake

  Hi I'm writing a client and a server for a realtime offshore simulator, and, as I have to send a lot of data through a socket, I'm using binary data to maximize the ammount of data I can send. I already know about integers endianness, and how to use htonl and ntohl to circumvent endianness issues, but my application, as almost all simulation software, deals with a lot of floats. My question is: Is there some issue of endianness whean dealing with binary formats of floating point numbers? I know that all the machines where my code will run use IEEE implementation of floating points, but is there some endianness issue when dealing with floats? Since I only have access to machines with the same endian, I cannot test this by myself. So, I'll be glad if someone can help me with this. Thanks in advance.

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