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  • Using dot To Access Object Attribute and Proper abstraction

    - by cobie
    I have been programming in python and java for quite a number of years and one thing i find myself doing is using the setters and getters from java in python but a number of blogs seem to think using the dot notation for access is the pythonic way. What I would like to know is if using dot to access methods does not violate abstraction principle. If for example I implement an attribute as a single object and use dot notation to access, if I wanted to change the code later so that the attribute is represented by a list of objects, that would require quite some heavy lifting which violates abstraction principle.

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  • What is the simplest human readable configuration file format?

    - by Juha
    Current configuration file is as follows: mainwindow.title = 'test' mainwindow.position.x = 100 mainwindow.position.y = 200 mainwindow.button.label = 'apply' mainwindow.button.size.x = 100 mainwindow.button.size.y = 30 logger.datarate = 100 logger.enable = True logger.filename = './test.log' This is read with python to a nested dictionary: { 'mainwindow':{ 'button':{ 'label': {'value':'apply'}, ... }, 'logger':{ datarate: {'value': 100}, enable: {'value': True}, filename: {'value': './test.log'} }, ... } Is there a better way of doing this? The idea is to get XML type of behavior and avoid XML as long as possible. The end user is assumed almost totally computer illiterate and basically uses notepad and copy-paste. Thus the python standard "header + variables" type is considered too difficult. The dummy user edits the config file, able programmers handle the dictionaries. Nested dictionary is chosen for easy splitting (logger does not need or even cannot have/edit mainwindow parameters).

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  • RPC protocols comparison

    - by Ricardo
    I have to select a protocol/technology to use for communicating a client-server architecture, with support both for Python and C. The main requirements are: Symmetrical communication in between ends: clients establish a connection and servers can send data back to clients through the same connection. Avoid excessive overhead by using HTTP or a big stack (if possible, TCP direct communication). TLS/SSL support for secure communications. Ease of implementation. For that, I evaluated the following protocols/communications technologies. Is the information on this table accurate and correct? (*1) TLS support for RPyC is based in a no-longer supported Python library.

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  • How to study for an Informatics Olympiad [on hold]

    - by Cloud
    One of my goals for next year is to participate in the Australian Informatics Olympiad. As far as I'm aware, it is not too different from Informatics Olympiads in other countries. What would be the best way to study for this? What content should I pay particular attention to while learning in Python? I am currently using the book 'Learn Python the hard way', but are there any other books worthy of a mention? This is the link to their site: http://orac.amt.edu.au/aio/ It contains sample questions, so you can get an idea for the structure or nature of the competition. I know this isn't really a specific programming question, but it would be great if someone could share their experience or give some suggestions for me.

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  • What do you think about gems and eggs? Alternatives?

    - by Juanlu001
    I've read recently some criticism (see 1, 2, 3) about the packaging distribution system of two popular programming languages: Ruby gems and Python eggs. The most important argument stated against them is that they replace the system package manager (in case there is one, as in every Linux distribution), which makes eggs and gems difficult to track, code difficult to patch, and so on. Are actually eggs and gems right? In case not, are there any alternatives to distributing Python or Ruby modules? Should developers focus on taking advantage of package manager (apt-get, pacman, ...) capabilities?

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  • chroot for unsecure programs execution

    - by attwad
    Hi, I have never set-up a chroot-jailed environment before and I am afraid I need some help to do it well. To explain shortly what this is all about: I have a webserver to which users send python scripts to process various files that are stored on the server (the system is for Research purpose). Everyday a cron job starts the execution of the uploaded scripts via a command of this kind: /usr/bin/python script_file.py All of this is really insecure and I would like to create a jail in which I would copy the necessary files (uploaded scripts, files to process, python binary and dependencies). I already looked at various utilities to create jails but none of them seemed up-to-date or were lacking solid documentation (ie. the links proposed in How can I run an untrusted python script) Could anyone guide me to a viable solution to my problem? like a working example of a script that creates a jail, put some files in it and executes a python script? Thank you very much.

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  • Do I have to learn html and javascript to create web applications?

    - by vainolo
    I am an experienced Java programmer, and I want to create a complex web application requiring dynamic pages, drawings, etc (take SO as an example). Do I have to learn javascript/html in order to create such an application? It is not that I don't want to learn another language (I've done this before), but technology on the javascript environment seems to change so fast that when you finish learning one framework it is already obsolete. I have checked a number of java framework for web development (spring, play), but not deeply. So can these frameworks (or other possible java frameworks that I'm not aware of) be used without learning html/javascript? I also have some python experience. So if I can do the app in python it is also an option.

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  • Embedding Pygame to C++ [closed]

    - by Pendertuga
    If embedding Pygame to C++ to have a game be an executable, is there any extra process I would have to use in order to use Pygame functions when embedding into C++? As opposed to just writing embedding code in C++ for normal Python code? To clear cut the question I want to know if it's the same process without having to call different functions. EDIT: My question is if I have to call different functions in C++ when embedding Python code that uses Pygame modules. I am NOT using pygame2exe nor py2exe. I never even mentioned those. My question is solely about code embedding.

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  • Why does Ubuntu's webkit inspector look just like Safari?

    - by NoBugs
    In older Ubuntu, the python-webkit inspector looked like Chrome, as you can see in these screenshots: http://stackoverflow.com/questions/13132459 (It had some annoying bugs, too.) I see Midori's inspector also looks just like Safari, and still has some bugs. In the latest 14.04's python-webkit embedded browser, the inspector actually looks just like Safari - and also seems to still have bugs (icons missing, problems selecting). Is there a reason for this drastic change, or is it just a default configuration? Is there a recommended way to get the webkit-inspector fully working?

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  • Error is occured when I try to build and install Numeric-24.2, anybody, help please me

    - by vpras
    vprasopchai@vprasopchai-Aspire-4720Z:~/Downloads/Numeric-24.2$ python setup.py build WARNING: '' not a valid package name; please use only.-separated package names in setup.py WARNING: '' not a valid package name; please use only.-separated package names in setup.py running build running build_py running build_ext MA Version 12.2.0 Numeric Version 24.2 vprasopchai@vprasopchai-Aspire-4720Z:~/Downloads/Numeric-24.2$ python setup.py install WARNING: '' not a valid package name; please use only.-separated package names in setup.py WARNING: '' not a valid package name; please use only.-separated package names in setup.py running install running build running build_py running build_ext running install_lib creating /usr/local/lib/python2.7/dist-packages/Numeric error: could not create '/usr/local/lib/python2.7/dist-packages/Numeric': Permission denied

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  • What are the parameters that let businesses choose .NET or Java over other languages/frameworks? [on hold]

    - by Othman
    Some of the biggest enterprise applications such as HR software, Sales and ERP, are written in .NET or Java. Also, Governments online solutions such as paying parking fines, and universities courses registration systems are all in .NET or Java. On the other hand, Facebook, Google and Wikipedia, are not using .NET or Java so much (Google uses at least both Java and Python). Twitter also was using Ruby for a long time, as well as Python. These websites work on much more data and at larger scales in terms of users and performance than any enterprise applications, yet still these companies have chosen a different path. What are the parameters driving such decisions? Note This question is not about why do you prefer x over y! or why those people are using this. The question is primarily asking about the parameters that makes Java Or .NET becomes better suite in enterprise applications based on Performance, Reliability, Scalability etc.

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  • What interface does python use to implement sockets?

    - by user2738698
    When I programmed in python, I believe I interfaced with the transport layer using sockets. If python was programmed by humans, they must have used an interface that was "lower" than sockets, to provide us with the interface to sockets. I assume firewalls, also programmed by humans, use interfaces of lower layers in the same manner, so is there a way to access such lower layers, in terms of programming?

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  • How do I create a custom python interpreter? i.e. with certain modules already included?

    - by Johnny Brown
    If you've used Ruby on Rails, I'm thinking of the feature where the user types 'rails console' and instantly gets a Ruby console with rails and the current app already loaded. I want to make something like this for a python program I'm working on, does anyone know how I would get to type say, 'python myPythonConsole.py' and open up a regular python interpreter but with my program and all its dependencies loaded?

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  • How do I copy a python function to a remote machine and then execute it?

    - by Hugh
    I'm trying to create a construct in Python 3 that will allow me to easily execute a function on a remote machine. Assuming I've already got a python tcp server that will run the functions it receives, running on the remote server, I'm currently looking at using a decorator like @execute_on(address, port) This would create the necessary context required to execute the function it is decorating and then send the function and context to the tcp server on the remote machine, which then executes it. Firstly, is this somewhat sane? And if not could you recommend a better approach? I've done some googling but haven't found anything that meets these needs. I've got a quick and dirty implementation for the tcp server and client so fairly sure that'll work. I can get a string representation the function (e.g. func) being passed to the decorator by import inspect string = inspect.getsource(func) which can then be sent to the server where it can be executed. The problem is, how do I get all of the context information that the function requires to execute? For example, if func is defined as follows, import MyModule def func(): result = MyModule.my_func() MyModule will need to be available to func either in the global context or funcs local context on the remote server. In this case that's relatively trivial but it can get so much more complicated depending on when and how import statements are used. Is there an easy and elegant way to do this in Python? The best I've come up with at the moment is using the ast library to pull out all import statements, using the inspect module to get string representations of those modules and then reconstructing the entire context on the remote server. Not particularly elegant and I can see lots of room for error. Thanks for your time

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  • Are there some cases where Python threads can safely manipulate shared state?

    - by erikg
    Some discussion in another question has encouraged me to to better understand cases where locking is required in multithreaded Python programs. Per this article on threading in Python, I have several solid, testable examples of pitfalls that can occur when multiple threads access shared state. The example race condition provided on this page involves races between threads reading and manipulating a shared variable stored in a dictionary. I think the case for a race here is very obvious, and fortunately is eminently testable. However, I have been unable to evoke a race condition with atomic operations such as list appends or variable increments. This test exhaustively attempts to demonstrate such a race: from threading import Thread, Lock import operator def contains_all_ints(l, n): l.sort() for i in xrange(0, n): if l[i] != i: return False return True def test(ntests): results = [] threads = [] def lockless_append(i): results.append(i) for i in xrange(0, ntests): threads.append(Thread(target=lockless_append, args=(i,))) threads[i].start() for i in xrange(0, ntests): threads[i].join() if len(results) != ntests or not contains_all_ints(results, ntests): return False else: return True for i in range(0,100): if test(100000): print "OK", i else: print "appending to a list without locks *is* unsafe" exit() I have run the test above without failure (100x 100k multithreaded appends). Can anyone get it to fail? Is there another class of object which can be made to misbehave via atomic, incremental, modification by threads? Do these implicitly 'atomic' semantics apply to other operations in Python? Is this directly related to the GIL?

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  • How do I read binary C++ protobuf data using Python protobuf?

    - by nbolton
    The Python version of Google protobuf gives us only: SerializeAsString() Where as the C++ version gives us both: SerializeToArray(...) SerializeAsString() We're writing to our C++ file in binary format, and we'd like to keep it this way. That said, is there a way of reading the binary data into Python and parsing it as if it were a string? Is this the correct way of doing it? binary = get_binary_data() binary_size = get_binary_size() string = None for i in range(len(binary_size)): string += i message = new MyMessage() message.ParseFromString(string) Update: Here's a new example, and a problem: message_length = 512 file = open('foobars.bin', 'rb') eof = False while not eof: data = file.read(message_length) eof = not data if not eof: foo_bar = FooBar() foo_bar.ParseFromString(data) When we get to the foo_bar.ParseFromString(data) line, I get this error: Exception Type: DecodeError Exception Value: Too many bytes when decoding varint. Update 2: It turns out, that the padding on the binary data was throwing protobuf off; too many bytes were being sent in, as the message suggests (in this case it was referring to the padding). This padding comes from using the C++ protobuf function, SerializeToArray on a fixed-length buffer. To eliminate this, I have used this temproary code: message_length = 512 file = open('foobars.bin', 'rb') eof = False while not eof: data = file.read(message_length) eof = not data string = '' for i in range(0, len(data)): byte = data[i] if byte != '\xcc': # yuck! string += data[i] if not eof: foo_bar = FooBar() foo_bar.ParseFromString(string) There is a design flaw here I think. I will re-implement my C++ code so that it writes variable length arrays to the binary file. As advised by the protobuf documentation, I will prefix each message with it's binary size so that I know how much to read when I'm opening the file with Python.

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  • Why can't I include these data files in a Python distribution using distutils?

    - by froadie
    I'm writing a setup.py file for a Python project so that I can distribute it. The aim is to eventually create a .egg file, but I'm trying to get it to work first with distutils and a regular .zip. This is an eclipse pydev project and my file structure is something like this: ProjectName src somePackage module1.py module2.py ... config propsFile1.ini propsFile2.ini propsFile3.ini setup.py Here's my setup.py code so far: from distutils.core import setup setup(name='ProjectName', version='1.0', packages=['somePackage'], data_files = [('config', ['..\config\propsFile1.ini', '..\config\propsFile2.ini', '..\config\propsFile3.ini'])] ) When I run this (with sdist as a command line parameter), a .zip file gets generated with all the python files - but the config files are not included. I thought that this code: data_files = [('config', ['..\config\propsFile1.ini', '..\config\propsFile2.ini', '..\config\propsFile3.ini'])] indicates that those 3 specified config files should be copied to a "config" directory in the zip distribution. Why is this code not accomplishing anything? What am I doing wrong? (I have also tried playing around with the paths of the config files... But nothing seems to help. Would Python throw an error or warning if the path was incorrect / file was not found?)

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  • Problem running python/matplotlib in background after ending ssh session.

    - by Jamie
    Hi there, I have to VPN and then ssh from home to my work server and want to run a python script in the background, then log out of the ssh session. My script makes several histogram plots using matplotlib, and as long as I keep the connection open everything is fine, but if I log out I keep getting an error message in the log file I created for the script. File "/Home/eud/jmcohen/.local/lib/python2.5/site-packages/matplotlib/pyplot.py", line 2058, in loglog ax = gca() File "/Home/eud/jmcohen/.local/lib/python2.5/site-packages/matplotlib/pyplot.py", line 582, in gca ax = gcf().gca(**kwargs) File "/Home/eud/jmcohen/.local/lib/python2.5/site-packages/matplotlib/pyplot.py", line 276, in gcf return figure() File "/Home/eud/jmcohen/.local/lib/python2.5/site-packages/matplotlib/pyplot.py", line 254, in figure **kwargs) File "/Home/eud/jmcohen/.local/lib/python2.5/site-packages/matplotlib/backends/backend_tkagg.py", line 90, in new_figure_manager window = Tk.Tk() File "/Home/eud/jmcohen/.local/lib/python2.5/lib-tk/Tkinter.py", line 1647, in __init__ self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use) _tkinter.TclError: couldn't connect to display "localhost:10.0" I'm assuming that it doesn't know where to create the figures I want since I close my X11 ssh session. If I'm logged in while the script is running I don't see any figures popping up (although that's because I don't have the show() command in my script), and I thought that python uses tkinter to display figures. The way that I'm creating the figures is, loglog() hist(list,x) ylabel('y') xlabel('x') savefig('%s_hist.ps' %source.name) close() The script requires some initial input, so the way I'm running it in the background is python scriptToRun.py << start>& logfile.log& Is there a way around this, or do I just have to stay ssh'd into my machine? Thanks.

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  • How to I pass parameters to Ruby/Python scripts from inside PHP?

    - by Roger
    Hi, everybody. I need to turn HTML into equivalent Markdown-structured text. From what I could discover, I have only two good choices: Python: Aaron Swartz's html2text.py Ruby: Singpolyma's html2markdown.rb As I am programming in PHP, I need to pass the HTML code, call the Ruby/Python Script and receive the output back. I started creating a simple test just to know if my server was configured to run both languages. PHP code: echo exec('./hi.rb'); Ruby code: #!/usr/bin/ruby puts "Hello World!" It worked fine and I am ready to go to the next step. Unfortunately, all I know is that the function is Ruby works like this: HTML2Markdown.new('<h1>HTMLcode</h1>').to_s I don't know how to make PHP pass the string (with the HTML code) to Ruby nor how to make the ruby script receive the variable and pass it back to PHP (after have parsed it into Markdown). Believe it or not: I know less of Python. A folk made a similar question here ("how to call ruby script from php?") but with no practical information to my case. Any help would be a joy - thanks. Rogério Madureira. atipico.com.br

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  • What are simple instructions for creating a Python package structure and egg?

    - by froadie
    I just completed my first (minor) Python project, and my boss wants me to package it nicely so that it can be distributed and called from other programs easily. He suggested I look into eggs. I've been googling and reading, but I'm just getting confused. Most of the sites I'm looking at explain how to use Python eggs that were already created, or how to create an egg from a setup.py file (which I don't yet have). All I have now is an Eclipse pydev project with about 4 modules and a settings/configuration file. In easy steps, how do I go about structuring it into folders/packages and compiling it into an egg? And once it's an egg, what do I have to know about deploying/building/using it? I'm really starting from scratch here, so don't assume I know anything; simple step-by-step instructions would be really helpful... These are some of the sites that I've been looking at so far: http://peak.telecommunity.com/DevCenter/PythonEggs http://www.packtpub.com/article/writing-a-package-in-python http://www.ibm.com/developerworks/library/l-cppeak3.html#N10232 I've also browsed a few SO questions but haven't really found what I need. Thanks!

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  • How to use python to create a GUI application which have cool animation/effects under Linux (like 3D

    - by sgon00
    Hi, I am not sure if my question title makes sense to you or not. I am seeing many cool applications which have cool animations/effects. I would like to learn how to use python to create this kind of GUI applications under Linux. "cool animation/effects" like 3D wall in Cooliris which is written in flash and compiz effects with opengl. I also heard of some python GUI library like wxPython and pyQT. Since I am completely new to python GUI programming, can anyone suggest me where to start and what I should learn to achieve and create such application? maybe learn pyQT with openGL feature? pyopengl binding? I have no clue on where to start. thank you very much for your time and suggestion. By the way, in case if someone need to know which kind of application I am going to create, well, just any kind of applications. maybe photo explorer with 3D wall, maybe IM client, maybe facebook client etc...

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  • Python CGI Premature end of script error depending on script parameters.

    - by nickengland
    I have a python script which should parse a file and produce some output to disk, as well as returning a webpage linking to the outputted files. When run with a file posted from the HTML form I get no HTML output back, just a 500 error page and the error_log contains the line: [Mon Apr 19 15:03:23 2010] [error] [client xxx.xxx.121.79] Premature end of script headers: uploadcml.py, referer: http://xxx.ch.cam.ac.uk:9000/ However, the files which the script should be saving are indeed saved to disk. If I run it without any arguments, the script returns the correct HTML indicating no file was parsed. All the information I have found on the web about Premature end of script headers implies it is due to either a missing header, or lack of permissions on the python script but neither can apply to me. The first lines of the script are: #!/home/nwe23/bin/bin/python import cgitb; cgitb.enable() import cgi import pybel,openbabel import random print "Content-Type: text/html" print so when run, I can see no way for it to fail to output the header, and it DOES output the header when run without a file to parse, but when given a file produces the error(but still parsed the file and saves the output to disk!). Does anyone know how this is happening and what can be done to fix it? I have tried adding wrongly-indented gibberish (such as foobar) at various points in the file, and this results in adding an indent error to the error_log wherever it is, even if its the very last line in the script. The Premature script headers error remains though. Does this mean the script is executing all the way through?

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  • How to find Tomcat's PID and kill it in python?

    - by 4herpsand7derpsago
    Normally, one shuts down Apache Tomcat by running its shutdown.sh script (or batch file). In some cases, such as when Tomcat's web container is hosting a web app that does some crazy things with multi-threading, running shutdown.sh gracefully shuts down some parts of Tomcat (as I can see more available memory returning to the system), but the Tomcat process keeps running. I'm trying to write a simple Python script that: Calls shutdown.sh Runs ps -aef | grep tomcat to find any process with Tomcat referenced If applicable, kills the process with kill -9 <PID> Here's what I've got so far (as a prototype - I'm brand new to Python BTW): #!/usr/bin/python # Imports import sys import subprocess # Load from imported module. if __init__ == "__main__": main() # Main entry point. def main(): # Shutdown Tomcat shutdownCmd = "sh ${TOMCAT_HOME}/bin/shutdown.sh" subprocess.call([shutdownCmd], shell=true) # Check for PID grepCmd = "ps -aef | grep tomcat" grepResults = subprocess.call([grepCmd], shell=true) if(grepResult.length > 1): # Get PID and kill it. pid = ??? killPidCmd = "kill -9 $pid" subprocess.call([killPidCmd], shell=true) # Exit. sys.exit() I'm struggling with the middle part - with obtaining the grep results, checking to see if their size is greater than 1 (since grep always returns a reference to itself, at least 1 result will always be returned, methinks), and then parsing that returned PID and passing it into the killPidCmd. Thanks in advance!

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  • In what order should the Python concepts be explained to absolute beginners?

    - by Tomaž Pisanski
    I am teaching Python to undergraduate math majors. I am interested in the optimal order in which students should be introduced to various Python concepts. In my view, at each stage the students should be able to solve a non-trivial programming problem using only the tools available at that time. Each new tool should enable a simpler solution to a familiar problem. A selection of numerous concepts available in Python is essential in order to keep students focused. They should also motivated and should appreciate each newly mastered tool without too much memorization. Here are some specific questions: For instance, my predecessor introduced lists before strings. I think the opposite is a better solution. Should function definitions be introduced at the very beginning or after mastering basic structured programming ideas, such as decisions (if) and loops (while)? Should sets be introduced before dictionaries? Is it better to introduce reading and writing files early in the course or should one use input and print for most of the course? Any suggestions with explanations are most welcome.

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  • Problems with Threading in Python 2.5, KeyError: 51, Help debugging?

    - by vignesh-k
    I have a python script which runs a particular script large number of times (for monte carlo purpose) and the way I have scripted it is that, I queue up the script the desired number of times it should be run then I spawn threads and each thread runs the script once and again when its done. Once the script in a particular thread is finished, the output is written to a file by accessing a lock (so my guess was that only one thread accesses the lock at a given time). Once the lock is released by one thread, the next thread accesses it and adds its output to the previously written file and rewrites it. I am not facing a problem when the number of iterations is small like 10 or 20 but when its large like 50 or 150, python returns a KeyError: 51 telling me element doesn't exist and the error it points out to is within the lock which puzzles me since only one thread should access the lock at once and I do not expect an error. This is the class I use: class errorclass(threading.Thread): def __init__(self, queue): self.__queue=queue threading.Thread.__init__(self) def run(self): while 1: item = self.__queue.get() if item is None: break result = myfunction() lock = threading.RLock() lock.acquire() ADD entries from current thread to entries in file and REWRITE FILE lock.release() queue = Queue.Queue() for i in range(threads): errorclass(queue).start() for i in range(desired iterations): queue.put(i) for i in range(threads): queue.put(None) Python returns with KeyError: 51 for large number of desired iterations during the adding/write file operation after lock access, I am wondering if this is the correct way to use the lock since every thread has a lock operation rather than every thread accessing a shared lock? What would be the way to rectify this?

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