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  • Simulating C-style for loops in python

    - by YGA
    (even the title of this is going to cause flames, I realize) Python made the deliberate design choice to have the for loop use explicit iterables, with the benefit of considerably simplified code in most cases. However, sometimes it is quite a pain to construct an iterable if your test case and update function are complicated, and so I find myself writing the following while loops: val = START_VAL while <awkward/complicated test case>: # do stuff ... val = <awkward/complicated update> The problem with this is that the update is at the bottom of the while block, meaning that if I want to have a continue embedded somewhere in it I have to: use duplicate code for the complicated/awkard update, AND run the risk of forgetting it and having my code infinite loop I could go the route of hand-rolling a complicated iterator: def complicated_iterator(val): while <awkward/complicated test case>: yeild val val = <awkward/complicated update> for val in complicated_iterator(start_val): if <random check>: continue # no issues here # do stuff This strikes me as waaaaay too verbose and complicated. Do folks in stack overflow have a simpler suggestion?

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  • Using Python tuples as vectors

    - by Etaoin
    I need to represent immutable vectors in Python ("vectors" as in linear algebra, not as in programming). The tuple seems like an obvious choice. The trouble is when I need to implement things like addition and scalar multiplication. If a and b are vectors, and c is a number, the best I can think of is this: tuple(map(lambda x,y: x + y, a, b)) # add vectors 'a' and 'b' tuple(map(lambda x: x * c, a)) # multiply vector 'a' by scalar 'c' which seems inelegant; there should be a clearer, simpler way to get this done -- not to mention avoiding the call to tuple, since map returns a list. Is there a better option?

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  • Python/Tkinter Audio Player

    - by Nicholas Quirk
    Hey everyone reading this, I've recently got into doing GUI development with Python. Tkinter seems like the easiest and most logical choice starting out. I did a little with wxPython but it was more sophisticated than what I needed. Anyway, I'm developing a media player. Right now it's a simple window with a button to load .wav files. The problem is I would like to implement a pause button now. But, when playing a audio file the GUI isn't accessible again (no buttons can be pushed) till the file is done playing. How can I make the GUI dynamic while an audio file is playing? I was thinking this maybe be because I'm using PyAudio, and their implementation doesn't allow this. Anyway, thanks for any advice before hand.

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  • Python threads all executing on a single core

    - by Rob Lourens
    I have a Python program that spawns many threads, runs 4 at a time, and each performs an expensive operation. Pseudocode: for object in list: t = Thread(target=process, args=(object)) # if fewer than 4 threads are currently running, t.start(). Otherwise, add t to queue But when the program is run, Activity Monitor in OS X shows that 1 of the 4 logical cores is at 100% and the others are at nearly 0. Obviously I can't force the OS to do anything but I've never had to pay attention to performance in multi-threaded code like this before so I was wondering if I'm just missing or misunderstanding something. Thanks.

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  • Python: Script works, but seems to deadlock after some time

    - by sberry2A
    I have the following script, which is working for the most part Link to PasteBin The script's job is to start a number of threads which in turn each start a subprocess with Popen. The output from each subprocess is as follows: 1 2 3 . . . n Done Bascially the subprocess is transferring 10M records from tables in one database to different tables in another db with a lot of data massaging/manipulation in between because of the different schemas. If the subprocess fails at any time in it's execution (bad records, duplicate primary keys, etc), or it completes successfully, it will output "Done\n". If there are no more records to select against for transfer then it will output "NO DATA\n" My intent was to create my script "tableTransfer.py" which would spawn a number of these processes, read their output, and in turn output information such as number of updates completed, time remaining, time elapsed, and number of transfers per second. I started running the process last night and checked in this morning to see it had deadlocked. There were not subprocceses running, there are still records to be updated, and the script had not exited. It was simply sitting there, no longer outputting the current information because no subprocces were running to update the total number complete which is what controls updates to the output. This is running on OS X. I am looking for three things: I would like to get rid of the possibility of this deadlock occurring so I don't need to check in on it as frequently. Is there some issue with locking? Am I doing this in a bad way (gThreading variable to control looping of spawning additional thread... etc.) I would appreciate some suggestions for improving my overall methodology. How should I handle ctrl-c exit? Right now I need to kill the process, but assume I should be able to use the signal module or other to catch the signal and kill the threads, is that right? I am not sure whether I should be pasting my entire script here, since I usually just paste snippets. Let me know if I should paste it here as well.

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  • Why is this logical expression in python False?

    - by W3ctor
    My question is, why are these expressions False? Python 2.6.4 (r264:75706, Dec 7 2009, 18:45:15) [GCC 4.4.1] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> num = raw_input("Choose a number: ") Choose a number: 5 >>> print num 5 >>> print ( num < 18 ) False >>> print ( num == 5 ) False Because if i try this: >>> print ( num > 0 ) True The expression works fine. Thank you for the help!

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  • Python Imaging: YCbCr problems

    - by daver
    Hi, I'm doing some image processing in Python using PIL, I need to extract the luminance layer from a series of images, and do some processing on that using numpy, then put the edited luminance layer back into the image and save it. The problem is, I can't seem to get any meaningful representation of my Image in a YCbCr format, or at least I don't understand what PIL is giving me in YCbCr. PIL documentation claims YCbCr format gives three channels, but when I grab the data out of the image using np.asarray, I get 4 channels. Ok, so I figure one must be alpha. Here is some code I'm using to test this process: import Image as im import numpy as np pengIm = im.open("Data\\Test\\Penguins.bmp") yIm = pengIm.convert("YCbCr") testIm = np.asarray(yIm) grey = testIm[:,:,0] grey = grey.astype('uint8') greyIm = im.fromarray(grey, "L") greyIm.save("Data\\Test\\grey.bmp") I'm expecting a greyscale version of my image, but what I get is this jumbled up mess: http://i.imgur.com/zlhIh.png Can anybody explain to me where I'm going wrong? The same code in matlab works exactly as I expect.

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  • c++ quick sort running time

    - by chnet
    I have a question about quick sort algorithm. I implement quick sort algorithm and play it. The elements in initial unsorted array are random numbers chosen from certain range. I find the range of random number effects the running time. For example, the running time for 1, 000, 000 random number chosen from the range (1 - 2000) takes 40 seconds. While it takes 9 seconds if the 1,000,000 number chosen from the range (1 - 10,000). But I do not know how to explain it. In class, we talk about the pivot value can effect the depth of recursion tree. For my implementation, the last value of the array is chosen as pivot value. I do not use randomized scheme to select pivot value. int partition( vector<int> &vec, int p, int r) { int x = vec[r]; int i = (p-1); int j = p; while(1) { if (vec[j] <= x){ i = (i+1); int temp = vec[j]; vec[j] = vec[i]; vec[i] = temp; } j=j+1; if (j==r) break; } int temp = vec[i+1]; vec[i+1] = vec[r]; vec[r] = temp; return i+1; } void quicksort ( vector<int> &vec, int p, int r) { if (p<r){ int q = partition(vec, p, r); quicksort(vec, p, q-1); quicksort(vec, q+1, r); } } void random_generator(int num, int * array) { srand((unsigned)time(0)); int random_integer; for(int index=0; index< num; index++){ random_integer = (rand()%10000)+1; *(array+index) = random_integer; } } int main() { int array_size = 1000000; int input_array[array_size]; random_generator(array_size, input_array); vector<int> vec(input_array, input_array+array_size); clock_t t1, t2; t1 = clock(); quicksort(vec, 0, (array_size - 1)); // call quick sort int length = vec.size(); t2 = clock(); float diff = ((float)t2 - (float)t1); cout << diff << endl; cout << diff/CLOCKS_PER_SEC <<endl; }

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  • Binary search of unaccesible data field in ldap from python

    - by EricR
    I'm interested in reproducing a particular python script. I have a friend who was accessing an ldap database, without authentication. There was a particular field of interest, we'll call it nin (an integer) for reference, and this field wasn't accessible without proper authentication. However, my friend managed to access this field through some sort of binary search (rather than just looping through integers) on the data; he would check the first digit, check if it was greater or less than the starting value, he would augment that until it returned a true value indicating existence, adding digits and continuing checking until he found the exact value of the integer nin. Any ideas on how he went about this? I've access to a similarly set up database.

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  • Unable to access LinkedIn conections using python rauth library

    - by srinath sastry
    I was trying out this example at https://github.com/litl/rauth/blob/master/examples/linkedin-web.py I get a 403, Access to connections denied error and it returns KeyError: '_total'. r_network option is present. Has anyone faced this issue? Also if you look at http://docs.python-requests.org/en/latest/user/quickstart/#oauth-authentication, the 'requests' library is initializing resource_owner_key, resource_owner_secret apart from the application keys. Not sure how these are getting passed from the 'rauth' library, Was wondering if that was causing this 403 error.

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  • Python: avoiding fraction simplification

    - by Anthony Labarre
    Hi all, I'm working on a music app' in Python and would like to use the fractions module to handle time signatures amongst other things. My problem is that fractions get simplified, i.e.: >>> from fractions import Fraction >>> x = Fraction(4, 4) >>> x Fraction(1, 1) However, it is important from a musical point of view that 4/4 stays 4/4 even though it equals 1. Is there any built-in way to avoid that behaviour? Thanks!

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  • Python - Things I shouldn't be doing?

    - by cornjuliox
    I've got a few questions about best practices in Python. Not too long ago I would do something like this with my code: ... junk_block = "".join(open("foo.txt","rb").read().split()) ... I don't do this anymore because I can see that it makes code harder to read, but would the code run slower if I split the statements up like so: f_obj = open("foo.txt", "rb") f_data = f_obj.read() f_data_list = f_data.split() junk_block = "".join(f_data_list) I also noticed that there's nothing keeping you from doing an 'import' within a function block, is there any reason why I should do that?

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  • List of IP addresses/hostnames from local network in Python

    - by joshhunt
    How can I get a list of the IP addresses or host names from a local network easily in Python? It would be best if it was multi-platform, but it needs to work on Mac OS X first, then others follow. Edit: By local I mean all active addresses within a local network, such as 192.168.xxx.xxx. So, if the IP address of my computer (within the local network) is 192.168.1.1, and I have three other connected computers, I would want it to return the IP addresses 192.168.1.2, 192.168.1.3, 192.168.1.4, and possibly their hostnames.

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  • Python: Trying to get index of an intersection

    - by user1620716
    I have the following line of code: for i in [i for i,x in enumerate(catdate) if x == set(NNSRCfile['datetimenew']).intersection(catdate)]: print i I am trying to find the index of the intersection for the two components above. Both are lengthy lists that have several commonalities. The intersection part works perfectly; however, the for loop seems to output nothing. (ie: there is nothing that is printed). Python outputs no error, and when I run the code in IPython, I notice that i is equivalent to to the very last element in the list "catdate", instead of listing the indices of "catdate" that are equivalent to the intersection values. Any help is greatly appreciated!

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  • Reading a triangle of numbers into a 2d array of ints in Python

    - by Gabriel Silk
    I want to read a triangle of integer values from a file into a 2D array of ints using Python. The numbers would look like this: 75 95 64 17 47 82 18 35 87 10 20 04 82 47 65 ... The code I have so far is as follows: f = open('problem18.input', 'r') arr = [] for i in range(0, 15): arr.append([]) str = f.readline() a = str.split(' ') for tok in a: arr[i].append(int(tok[:2])) print arr I have a feeling this could be done in a tighter, more Pythonesque way. How would you do it?

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  • Python code that needs some overview

    - by fabio
    Hi guys, im currently learning python (in the very begining), so I still have some doubts about good code manners and how should I proceed with it. Today I created this code that should random trought 01 to 60 (but is running from 01 to 69) import random dez = ['0', '1', '2', '3', '4', '5', '6'] uni = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'] sort = [] while len(sort) <= 5: random.shuffle(dez) random.shuffle(uni) w = random.choice(dez) z = random.choice(uni) chosen = str(w) + str(z) if chosen != "00" and chosen not in sort: sort.append(chosen) print chosen I'm also in doubt how to make the code stop at "60".

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  • syntax error in python:

    - by pecker
    Hello, I'm learning python. It gives syntax error in this script. I'm unable to figure out. import exceptions class FOUND(Exception): pass x = [1,2,3,4,56,73,29,35,12,32,63,12,76,75,89] while True: test = int(raw_input('Enter integer to be checked in list:')) try: count = -1 for y in x: count += 1 if y == test: raise FOUND except ValueError,e: print "Not a valid integer (%d)"%(e) except FOUND: print "Found (%d) at (%d)"%(test,count) else: print "Not found ,Appending (%d) to list at location (%d)"%(test,count+1) x.append(test) finally: print "The List:" print x print " " Invalid syntax & it highlights comma in this line: 'except ValueError,e:'

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  • Problem about python import with error

    - by xiao
    Hello, I have write a small python module with one class and two functions. The skeleton of the module is as following: #file name: test_module.py class TestClass: @classmethod def method1(cls, param1): #to do something pass def __init__(self, param1): #to do something ... def fun1(*params): #to do something ... def fun2(*params): #to do something ... Another py file is a small script which imports function and class from the module, as following: import sys from test_module import TestClass, fun1, fun2 def main(sys_argv): li = range(5) inst1 = TestClass(li) fun1(inst1) fun2(inst1) return if __name__ == "__main__": main(sys.argv) But when I execute the script, it is broken with following message: ./script.py: line 4: syntax error near unexpected token `(' ./script.py: line 4: `def main(sys_argv):' I am not sure what the problem is. Is it a problem with import? But when I try to import the module in ipython, everything is just ok.

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  • Load JSON in Python as header character set

    - by mridang
    Hi everyone, I've always found character sets and encodings complicated to understand and here I'm faced with another problem. My apologies for any inaccuracies. I'll do my best. I'm requesting data from a server which returns JSON. In the HTTP headers it also returns the character set like so: Content-Type: text/html; charset=UTF-8 I'm using the JSON library in Python to load the JSON using the json.loads method. When I pass it the returned JSON, it gives me a dictionary in Unicode. I've Googled around and I know that JSON should return Unicode as JavaScript strings are Unicode objects. How can I load the JSON as UTF-8? I would like to use the same encoding as specified in the response header. I've read this post but it didn't help. Thank you.

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  • How to use OpenCV in Python?

    - by Roman
    I have just installed OpenCV on my Windows 7 machine. As a result I get a new directory: C:\OpenCV2.2\Python2.7\Lib\site-packages In this directory I have two files: cv.lib and cv.pyd. Then I try to use the opencv from Python. I do the following: import sys sys.path.append('C:\OpenCV2.2\Python2.7\Lib\site-packages') import cv As a result I get the following error message: File "<stdin>", line 1, in <module> ImportError: DLL load failed: The specified module could not be found. What am I doing wrong? ADDED As it was recommended here, I have copied content of C:\OpenCV2.0\Python2.6\Lib\site-packages to the C:\Python26\Lib\site-packages. It did not help.

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  • python: list modules within the package

    - by ak
    I have a package with a few modules, each module has a class (or a few classes) defined within it. I need to get the list of all modules within the package. Is there an API for this in python? Here is the file structure: \pkg\ \pkg\__init__.py \pkg\module1.py -> defines Class1 \pkg\module2.py -> defines Class2 \pkg\module3.py -> defines Class3 and Class31 from within module1 I need to get the list of modules within pkg, and then import all the classes defined in these modules Thanks ak

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  • Python: Elegant way to check if at least one regex in list matches a string

    - by houbysoft
    Hi. I have a list of regexes in python, and a string. Is there an elegant way to check if the at least one regex in the list matches the string? By elegant, I mean something better than simply looping through all of the regexes and checking them against the string and stopping if a match is found. Basically, I had this code: list = ['something','another','thing','hello'] string = 'hi' if string in list: pass # do something else: pass # do something else Now I would like to have some regular expressions in the list, rather than just strings, and I am wondering if there is an elegant solution to check for a match to replace if string in list:. Thanks in advance.

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  • Automatic logout in python web app

    - by Ali
    I have a web application in python wherein the user submits their email and password. These values are compared to values stored in a mysql database. If successful, the script generates a session id, stores it next to the email in the database and sets a cookie with the session id, with allows the user to interact with other parts of the sight. When the user clicks logout, the script erases the session id from the database and deletes the cookie. The cookie expires after 5 hours. My concern is that if the user doesnt log out, and the cookie expires, the script will force him to login, but if he has copied the session id from before, it can still be validated. How do i automatically delete the session id from the mysql database after 5 hours?

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  • Testing with Unittest Python

    - by chrissygormley
    Hello, I am runninig test's with Python Unittest. I am running tests but I want to do negative testing and I would like to test if a function throw's an exception, it passes but if no exception is thrown the test fail's. The script I have is: try: result = self.client.service.GetStreamUri(self.stream, self.token) self.assertFalse except suds.WebFault, e: self.assertTrue else: self.assertTrue This alway's passes as True even when the function work's perfectly. I have also tried various other way's including: try: result = self.client.service.GetStreamUri(self.stream, self.token) self.assertFalse except suds.WebFault, e: self.assertTrue except Exception, e: self.assertTrue Does anyone have any suggestions? Thanks

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