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  • side effect gotchas in python/numpy? horror stories and narrow escapes wanted

    - by shabbychef
    I am considering moving from Matlab to Python/numpy for data analysis and numerical simulations. I have used Matlab (and SML-NJ) for years, and am very comfortable in the functional environment without side effects (barring I/O), but am a little reluctant about the side effects in Python. Can people share their favorite gotchas regarding side effects, and if possible, how they got around them? As an example, I was a bit surprised when I tried the following code in Python: lofls = [[]] * 4 #an accident waiting to happen! lofls[0].append(7) #not what I was expecting... print lofls #gives [[7], [7], [7], [7]] #instead, I should have done this (I think) lofls = [[] for x in range(4)] lofls[0].append(7) #only appends to the first list print lofls #gives [[7], [], [], []] thanks in advance

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  • The confusion on python encoding

    - by zhangzhong
    I retrieved the data encoded in big5 from database,and I want to send the data as email of html content, the code is like this: html += """<tr><td>""" html += """unicode(rs[0], 'big5')""" # rs[0] is data encoded in big5 I run the script, but the error raised: UnicodeDecodeError: 'ascii' codec can't decode byte...... However, I tried the code in interactive python command line, there are no errors raised, could you give me the clue?

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  • whats the diference between train, validation and test set, in neural networks?

    - by Daniel
    Im using this library http://pastebin.com/raw.php?i=aMtVv4RZ to implement a learning agent. I have generated the train cases, but i dont know for sure what are the validation and test sets, the teacher says: 70% should be train cases, 10% will be test cases and the rest 20% should be validation cases. Thanks. edit i have this code, for training.. but i have no ideia when to stop training.. def train(self, train, validation, N=0.3, M=0.1): # N: learning rate # M: momentum factor accuracy = list() while(True): error = 0.0 for p in train: input, target = p self.update(input) error = error + self.backPropagate(target, N, M) print "validation" total = 0 for p in validation: input, target = p output = self.update(input) total += sum([abs(target - output) for target, output in zip(target, output)]) #calculates sum of absolute diference between target and output accuracy.append(total) print min(accuracy) print sum(accuracy[-5:])/5 #if i % 100 == 0: print 'error %-14f' % error if ? < ?: break

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  • How to parse XML file to get specific data effectively

    - by Carlos_Liu
    I have an XML file looks like this: <?xml version="1.0" encoding="utf-8" ?> <PathMasks> <Mask desc="Masks_X1"> <config id="01" mask="88" /> <config id="03" mask="80" /> <config id="51" mask="85" /> </Mask> <Mask desc="Masks_X2"> <config id="70" mask="1" /> <config id="73" mask="6" /> </Mask> <Types> <path id="01" desc="TC->PP1" /> <path id="02" desc="TC->PP2" /> <path id="03" desc="TC->PPn" /> </Types> </PathMasks> How to parse the file and get all the data of Mask_X1 as following: id value ===== 01, 88 03, 80 51, 85

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  • Learning Lisp - Why ?

    - by David
    I really feel that I should learn Lisp and there are plenty of good resources out there to help me do it. I'm not put off by the complicated syntax, but where in "traditional commercial programming" would I find places it would make sense to use it instead of a procedural language. Is there a commercial killer-app out there that's been written in Lisp ?

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  • How do you setLayoutParams() for an ImageView?

    - by DeadTime
    I want to set the LayoutParams for an ImageView but cant seem to find out the proper way to do it. I can only find documentation in the API for the various ViewGroups, but not an ImageView. Yet the ImageView seems to have this functionality. This code doesn't work... myImageView.setLayoutParams(new ImageView.LayoutParams(30,30)); How do I do it?

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  • Inserting multiple types into an SQLite database with Python

    - by mankoff
    I'm trying to create an SQLite 3 database from Python. I have a few types I'd like to insert into each record: A float, and then 3 groups of n floats, currently a tuple but could be an array or list.. I'm not well-enough versed in Python to understand all the differences. My problem is the INSERT statement. DAS = 12345 lats = (42,43,44,45) lons = (10,11,12,13) times = (1,2,3,4,5,6,7,8,9) import sqlite3 connection = sqlite3.connect("test.db") cursor = connection.cursor() cursor.execute( "create table foo(DAS LONG PRIMARY KEY,lats real(4),lons real(4), times real(9) )" ) I'm not sure what comes next. Something along the lines of: cmd = 'INSERT into foo values (?,?,?,?), ..." cursor.execute(cmd) How should I best build the SQL insert command given this data?

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  • View Animation (Resizing a Ball)

    - by user270811
    hi, i am trying to do this: 1) user long touches the screen, 2) a circle/ball pops up (centered around the user's finger) and grows in size as long as the user is touching the screen 3) once the user lets go of the finger, the ball (now in its final size) will bounce around. i think i have the bouncing around figure out from the DivideAndConquer example, but i am not sure how to animate the ball's growth. i looked at various view flipper examples such as this: http://www.inter-fuser.com/2009/08/android-animations-3d-flip.html but it seems like view flipper is best for swapping two static pictures. i wasn't able to find a good view animator example other than the flippers. also, i would prefer to use images as opposed to just a circle. can someone point me in the right direction? thanks.

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  • Why do I not get the correct answer for Euler 56 in J?

    - by Gregory Higley
    I've solved 84 of the Project Euler problems, mostly in Haskell. I am now going back and trying to solve in J some of those I already solved in Haskell, as an exercise in learning J. Currently, I am trying to solve Problem 56. Let me stress that I already know what the right answer is, since I've already solved it in Haskell. It's a very easy, trivial problem. I will not give the answer here. Here is my solution in J: digits =: ("."0)":"0 eachDigit =: adverb : 'u@:digits"0' NB. I use this so often I made it an adverb. cartesian =: adverb : '((#~ #) u ($~ ([:*~#)))' >./ +/ eachDigit x: ^ cartesian : i. 99 This produces a number less than the desired result. In other words, it's wrong somehow. Any J-ers out there know why? I'm baffled, since it's pretty straightforward and totally brute force.

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  • Do I correctly understand what a class is?

    - by Matt
    I've had trouble finding a clear, concise laymans definition of a class. Usually, they give general ideas without specifically spelling it out, and I'm wondering if I'm understanding this correctly. As I understand it, a class is the set of code that controls an object. For example, in an app that has a button for 'Yes' and a button for 'No', and a text box for output, the code that tells the computer what to do when the user uses the Yes button is one class, the code for hitting No is another class, and an object is the two buttons and what they do together to influence the output box. Am I right, or am I confusing terms here? Thanks

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  • How to get the original variable name of variable passed to a function

    - by Acorn
    Is it possible to get the original variable name of a variable passed to a function? E.g. foobar = "foo" def func(var): print var.origname So that: func(foobar) Returns: >>foobar EDIT: All I was trying to do was make a function like: def log(soup): f = open(varname+'.html', 'w') print >>f, soup.prettify() f.close() .. and have the function generate the filename from the name of the variable passed to it. I suppose if it's not possible I'll just have to pass the variable and the variable's name as a string each time.

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  • [mysql] diff between tables

    - by www.yegorov-p.ru
    I have two tables, with the same structure, for example: table "first' with columns 'a','b','c' and table 'second' with the same columns. How to find difference betweet those two tables? Of course, I can make some script on python, that will make set(a)-set(b), but I think there is some way to do it in mysql.

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  • Comparing a time delta in python

    - by Alpesh Patel
    I have a variable which is <type 'datetime.timedelta'> and I would like to compare it against certain values. Lets say d produces this datetime.timedelta value 0:00:01.782000 I would like to compare it like this: #if d is greater than 1 minute if d>1:00: print "elapsed time is greater than 1 minute" I have tried converting datetime.timedelta.strptime() but that does seem to work. Is there an easier way to compare this value?

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  • Basic Array Iteration in Ruby

    - by michaelmichael
    What's a better way to traverse an array while iterating through another array? For example, if I have two arrays like the following: names = [ "Rover", "Fido", "Lassie", "Calypso"] breeds = [ "Terrier", "Lhasa Apso", "Collie", "Bulldog"] Assuming the arrays correspond with one another - that is, Rover is a Terrier, Fido is a Lhasa Apso, etc. - I'd like to create a dog class, and a new dog object for each item: class Dog attr_reader :name, :breed def initialize(name, breed) @name = name @breed = breed end end I can iterate through names and breeds with the following: index = 0 names.each do |name| dog = Dog.new("#{name}", "#{breeds[index]}") index = index.next end However, I get the feeling that using the index variable is the wrong way to go about it. What would be a better way?

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  • How do I make lines scale when using GLOrtho?

    - by Mason Wheeler
    I'm using GLOrtho to set up a 2D view that I can render textures onto. It works really well, up until I try to zoom in on the image. If I pass half the width and half the height of the viewport to GLOrtho, I end up with all my textures displayed twice as big as normal, which is exactly what I expect. But then I try to draw a box around part of the image and it all falls apart. I call glBegin(GL_LINE_LOOP), place the four vertices, and call glEnd, and I expect to see the same thing I would see if I drew it at normal zoom level, doubled. Instead, I get lines that are all the right length, but they all come out one pixel wide, instead of two, and it looks really bad. What am I missing?

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  • Problem running a Python program, error: Name 's' is not defined.

    - by Sergio Tapia
    Here's my code: #This is a game to guess a random number. import random guessTaken = 0 print("Hello! What's your name kid") myName = input() number = random.randint(1,20) print("Well, " + myName + ", I'm thinking of a number between 1 and 20.") while guessTaken < 6: print("Take a guess.") guess = input() guess = int(guess) guessTaken = guessTaken + 1 if guess < number: print("You guessed a little bit too low.") if guess > number: print("You guessed a little too high.") if guess == number: break if guess == number: guessTaken = str(guessTaken) print("Well done " + myName + "! You guessed the number in " + guessTaken + " guesses!") if guess != number: number = str(number) print("No dice kid. I was thinking of this number: " + number) This is the error I get: Name error: Name 's' is not defined. I think the problem may be that I have Python 3 installed, but the program is being interpreted by Python 2.6. I'm using Linux Mint if that can help you guys help me. Using Geany as the IDE and pressing F5 to test it. It may be loading 2.6 by default, but I don't really know. :( Edit: Error 1 is: File "GuessingGame.py", line 8, in <Module> myName = input() Error 2 is: File <string>, line 1, in <Module>

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  • Codeigniter: Checklist for new users & logistics of app

    - by Kevin Brown
    I'm developing my first web-app, and I'm working through logistics. New users (At first login) need to complete a few things before they can use the app fully. For example, they need to complete their profile before they can move on to step 2, which is taking a test. What's the best way to go about creating a "new-user" checklist? I want it to be as simple as possible, coding wise, and as easy as possible for the user.

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  • Need to add underscore to my regex

    - by TaMeR
    I suck at regular expression and just can't seem to figure this out. '/^[A-Za-z0-9](?:.[A-Za-z0-9]+)*$/' As it's right now it allows dots anytime after the first char and I like to add _ so that it allows both. Thanks

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