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  • What is the justification for Python's power operator associating to the right?

    - by Pieter Müller
    I am writing code to parse mathematical expression strings, and noticed that the order in which chained power operators are evaluated in Python differs from the order in Excel. From http://docs.python.org/reference/expressions.html: "Thus, in an unparenthesized sequence of power and unary operators, the operators are evaluated from right to left (this does not constrain the evaluation order for the operands): -1*2 results in -1."* This means that, in Python: 2**2**3 is evaluated as 2**(2**3) = 2**8 = 256 In Excel, it works the other way around: 2^2^3 is evaluated as (2^2)^3 = 4^3 = 64 I now have to choose an implementation for my own parser. The Excel order is easier to implement, as it mirrors the evaluation order of multiplication. I asked some people around the office what their gut feel was for the evaluation of 2^2^3 and got mixed responses. Does anybody know of any good reasons or conciderations in favour of the Python implementation? And if you don't have an answer, please comment with the result you get from gut feel - 64 or 256?

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  • What advantages switching to ruby might give me as a python programmer ?

    - by Richard Placide
    This is my first question on stackoverflow, so please bear with me. I'm trying to stay away from any form of trolling or flame baiting as i have a tremendous respect for both languages. I'm a python programmer (though not an expert) and i love it. My first language was C++. My line of work (web development) is pushing me towards other languages like php and javascript. Recently, I've been very excited by Ruby's increasing popularity. However I used to be under the impression that Python and Ruby were so close that there was little point in trying to learn and master both. But I get the sense that I was wrong, hence my question : I'd like to hear from python programmers who have either switched entirely to ruby or added ruby to their toolset. What specific benefits did you get from switching (entirely or partially) to Ruby from Python ? Ideally I'd like to hear from real world experiences.

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  • Can I debug with python debugger when using py.test somehow?

    - by Joel
    I am using py.test for unit testing my python program. I wish to debug my test code with the python debugger the normal way (by which i mean pdb.set_trace() in the code) but I can't make it work. Putting pdb.set_trace() in the code doesn't work (raises IOError: reading from stdin while output is captured). I have also tried running py.test with the option --pdb but that doesn't seem to do the trick if I want to explore what happens before my assertion. It breaks when an assertion fails, and moving on from that line means terminating the program. Does anyone know a way to get debugging, or is debugging and py.test just not meant to be together?

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  • Run Python Server at Startup

    - by DizzyDoo
    Hello, I've got a few Python based servers that I need to run, and would like them to start automatically when I start my Ubuntu Server box. What is the best way to execute them like this? I was hoping I could write a Bash script and use Screen to get them running in the background, where I can check on them every now and then, but where as echo screen -d -m python works just fine, echo screen -d -m `sudo python /home/matt/tornadoServer/tornadoDeploy.py` doesn't, with no error messages. Is that something to do with the spaces? Even though I did surround it with backquotes? I also tried: WEB="screen -d -m `sudo python /home/matt/tornadoServer/tornadoDeploy.py`" echo $WEB As a way of escaping the spaces, but no luck. What's Bash scripting way to do this? And, once the Bash script works, where can I put it to make it execute on startup?

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  • Installing Python in Windows XP

    - by Sam
    My work PC has restrictions that stop me from adding programs to the start menu so when I try to install Python using the Python 2.6.5 Windows installer it can't complete as it tries to add a shortcut to my start menu. Is there a way around this? I.e another way of installing without the need for a shortcut? I've tried Python portable but as it doesn't add anything to the registry it can't be detected.

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  • How should I do custom sort in Python 3?

    - by S.Mark
    In Python 2.x, I could pass custom function to sorted and .sort functions >>> x=['kar','htar','har','ar'] >>> >>> sorted(x) ['ar', 'har', 'htar', 'kar'] >>> >>> sorted(x,cmp=customsort) ['kar', 'htar', 'har', 'ar'] Because, in My language, consonents are comes with this order "k","kh",....,"ht",..."h",...,"a" But In Python 3.x, looks like I could not pass cmp keyword >>> sorted(x,cmp=customsort) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'cmp' is an invalid keyword argument for this function Is there any alternatives or should I write my own sorted function too?

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  • Install Python 2.4 or newer on Centos 4.x

    - by TomA
    I would like to use Python 2.4 features in my Django apps running on CentOS 4.7. The default version of Python is 2.3 and I think it would be best not to try replace it. Is there a way to install a newer version of Python alongside and somehow tell Apache to use that for mod_python?

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  • How can I change the wallpaper using a Python script?

    - by furtelwart
    I want to change my wallpaper in Ubuntu 11.10 (with Unity) in a small Python script. I found the possibility to change it via the gconf-editor in /desktop/gnome/background/picture_filename. With python-gconf, I'm able to change the necessary values. Apparently, the gconf string is not read out. If I change it (either via a script or via gconf-editor), the wallpaper remains and in the menu of "Change wallpaper", the old wallpaper is shown. How am I able to change the wallpaper for Unity via a Python script? The following code does work. Apparently, the gsettings are only applied, if some Gtk code is executed. #!/usr/bin/python # -*- coding: utf-8 -*- from gi.repository import Gtk, Gio class BackgroundChanger(): SCHEMA = 'org.gnome.desktop.background' KEY = 'picture-uri' def change_background(self, filename): gsettings = Gio.Settings.new(self.SCHEMA) print(gsettings.get_string(self.KEY)) print(gsettings.set_string(self.KEY, "file://" + filename)) Gtk.Window() print(gsettings.get_string(self.KEY)) if __name__ == "__main__": BackgroundChanger().change_background("/home/user/existing.jpg")

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  • Trouble typing accented letters at the terminal prompt after launching Python

    - by Nicojo
    Edit: Using Mac OSX 10.6, whether I use Terminal.app or iTerm.app, when I launch Python, I can no longer type accented letters (e.g.é or ä). Any ideas? ORIGINAL POST: I am using iTerm 0.10. I would like to type in a string with accented characters (e.g. é) but when I do so at the iTerm prompt, no character appears. This does not occur in Terminal. Could someone help me find out what the problem is, and eventually fix it? EDIT: In Terminal.app, I can use accented characters. However, when I launch the Python 2.71 prompt, I can no longer type in accented characters. When I quit python and return to the terminal prompt, I can again type accented characters. In iTerm, although I quit Python and restarted iTerm, I cannot type in accented characters (I do not know if I could before).

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  • Besides macros, are there any other metaprogramming techniques?

    - by mhr
    I'm making a programming language, and, having spent some time in Lisp/Scheme, I feel that my language should be malleable. Should I use macros, or is there something else I might/should use? Is malleable syntax even a good idea? Is it perhaps too powerful a concept? EDIT: In doing some research, I found fexprs. I don't really understand what these are. Help with that in an answer too please. EDIT2: Is it possible to have a language with macros/something-of-a-similar-nature without having s-expressions?

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  • How does Python compile some its code in C?

    - by Howcan
    I read that some constructs of Python are more efficient because they are compiled in C. https://wiki.python.org/moin/PythonSpeed/PerformanceTips Some of the examples used were map() and filter(). I was wondering how Python is able to do this? It's generally interpreted, so how does some of the code get compiled while another is interpreted - and in a different language? Why not just compile the whole thing?

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  • How to check for palindrome using Python logic

    - by DrOnline
    My background is only a 6 month college class in basic C/C++, and I'm trying to convert to Python. I may be talking nonsense, but it seems to me C, at least at my level, is very for-loop intensive. I solve most problems with these loops. And it seems to me the biggest mistake people do when going from C to Python is trying to implement C logic using Python, which makes things run slowly, and it's just not making the most of the language. I see on this website: http://hyperpolyglot.org/scripting (serach for "c-style for", that Python doesn't have C-style for loops. Might be outdated, but I interpret it to mean Python has its own methods for this. I've tried looking around, I can't find much up to date (Python 3) advice for this. How can I solve a palindrome challenge in Python, without using the for loop? I've done this in C in class, but I want to do it in Python, on a personal basis. The problem is from the Euler Project, great site btw. def isPalindrome(n): lst = [int(n) for n in str(n)] l=len(lst) if l==0 || l==1: return True elif len(lst)%2==0: for k in range (l) ##### else: while (k<=((l-1)/2)): if (list[]): ##### for i in range (999, 100, -1): for j in range (999,100, -1): if isPalindrome(i*j): print(i*j) break I'm missing a lot of code here. The five hashes are just reminders for myself. Concrete questions: 1) In C, I would make a for loop comparing index 0 to index max, and then index 0+1 with max-1, until something something. How to best do this in Python? 2) My for loop (in in range (999, 100, -1), is this a bad way to do it in Python? 3) Does anybody have any good advice, or good websites or resources for people in my position? I'm not a programmer, I don't aspire to be one, I just want to learn enough so that when I write my bachelor's degree thesis (electrical engineering), I don't have to simultaneously LEARN an applicable programming language while trying to obtain good results in the project. "How to go from basic C to great application of Python", that sort of thing. 4) Any specific bits of code to make a great solution to this problem would also be appreciated, I need to learn good algorithms.. I am envisioning 3 situations. If the value is zero or single digit, if it is of odd length, and if it is of even length. I was planning to write for loops... PS: The problem is: Find the highest value product of two 3 digit integers that is also a palindrome.

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  • What should I think about when switching from Python to Java?

    - by Nick Rosencrantz
    I was a Java developer in the early 2000s, switched to Python in 2008 and now Iäm working in Java again. Is there anything special you think I should keep in mind when going back to a Java environment? I used to work with EJB 1.0, I didn't work with EJB 2.0 and now we have JPA instead. I'm comfortable programming in Java and my new job with Java is much better than my Python job even though Python is my favorite language the tools and others things about my Java job makes it much better. I found when I searched jobs that demand for Java developer was much greater than demand for Python programmers- do you have a similar experience? Thank you

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  • Windows is not passing command line arguments to Python programs executed from the shell.

    - by mckoss
    I'm having trouble getting command line arguments passed to Python programs if I try to execute them directly as executable commands from a Windows command shell. For example, if I have this program (test.py): import sys print "Args: %r" % sys.argv[1:] And execute: >test foo Args: [] as compared to: >python test.py foo Args: ['foo'] My configuration has: PATH=...;C:\python25;... PATHEXT=...;.PY;.... >assoc .py .py=Python.File >ftype | grep Python Python.CompiledFile="C:\Python25\python.exe" "%1" %* Python.File="C:\Python25\python.exe" "%1" %* Python.NoConFile="C:\Python25\pythonw.exe" "%1" %*

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  • Why is the Python interpreter provided by Django suddenly showing me Python tab completion upon a single Tab press?

    - by ysim
    This issue seems to have just started happening; basically I just noticed that whenever I press the Tab key in the Python interpreter that comes with Django, it gives me the Display all ... possibilities? (y or no) prompt. I opened a similar question just now, where I noticed that removing set show-all-if-ambiguous on from .inputrc fixed the problem in the non-Django Python interpreter that was showing me bash tab completion, but the problem persists with the Django one, only with Python tab completion. It's very odd and it seems to have come out of nowhere. There's nothing else in my .inputrc other than set completion-ignore-case on, which shouldn't be conflicting with the Python interpreter, but I've also tried removing that (leaving my .inputrc blank), but it's still happening. I'm not sure why this is suddenly happening, but it would be great if someone had an idea of why and how to fix it.

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  • Should we use python 2.6 or 2.7 or 3.x?

    - by lamwaiman1988
    The version of python which I am using is 2.6, and there is a 2.7 and 3.x. Usually I use python for some trivial program/snippet. I realize there are some major difference between 2.x and 3.x. I would really like to know, if I am going to make a bigger project with python, which version of python should I use? Should I upgrade to 2.7, or go to 3.x or stay with 2.6? The decision should be based on these terms: Number of user in the internet as a community. More users mean more open-source package and help from them. Functionality. Support from official development team. Compatibility for existing module/package. Thanks!

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  • Computer Graphics: Principles and Practice in C ( in Python? )

    - by user29163
    I am attending a Computer graphics course after the summer. I have read lots of good things about the book "Computer Graphics: Principles and Practice in C" for people who are willing to put in some work. My school does not focus on C/C++ until next year, so I have decided to learn Python this summer and get good at Python this following year. How language dependent is this book? Can I work through it in Python?

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  • I am having a hard time learning Python, is it just me? [closed]

    - by Carpet
    For the past two weeks I am trying to learn Python and a framework for web development, while doing so I learned a lot but not what I was looking for. I did manage to get everything set up and running, followed tutorials, but I still have not managed to create a navigation bar and a simple template website. My goal is to create web applications (like a blog) and perhaps platforms similar to stackoverflow. In which language was stackoverflow created in? I believe that Python Django or Python Tornado (which I tried) is more for people who have learned desktop application development. It is hard for me to make sense out of the complex and fragmented system. I'm able to develop with PHP and have already created blogs and similar applications. If Python and a framework is not for me, what type of language would be for me, which languages are used for these type of platforms, I would like to develop myself? I only omitted PHP because I found it later on a bit too inheriting, and the code is hardly readable and becomes quickly cluttered, I love how readable Python code is.

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  • Purge complete Python installation on OS X

    - by Konrad Rudolph
    I’m working on a recently-upgraded OS X Snow Leopard and MacPorts and I’m running into problems at every corner. The first problem is the sheer number of installed Python versions: altogether, there are four: 2.5, 2.6 and 3.0 in /Library/Frameworks/Python.framework 2.6 in /opt/local/Library/Frameworks/Python.framework/ (MacPorts installation) So there are at least two useless/redundant versions: 2.5 and the redundant 2.6. Additionally, the pre-installed Python is giving me severe problems because some of the pre-installed libraries (in particular, scipy, numpy and matplotlib) don’t work properly. I am sorely tempted to purge the complete /Library/Frameworks/Python.framework path, as well as the MacPorts Python installation. After that, I’ll start from a clean slate by installing a properly configured Python, e.g. that from Enthought. Am I running headlong into trouble? Or is this a sane undertaking? (In particular, I need a working Python in the next few days and if I end up with a non-working Python this would be a catastrophe of medium proportions. On the other hand, some features I need from matplotlib aren’t working now.)

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  • Python 3.0 IDE - Komodo and Eclipse both flaky?

    - by victorhooi
    heya, I'm trying to find a decent IDE that supports Python 3.x, and offers code completion/in-built Pydocs viewer, Mercurial integration, and SSH/SFTP support. Anyhow, I'm trying Pydev, and I open up a .py file, it's in the Pydev perspective and the Run As doesn't offer any options. It does when you start a Pydev project, but I don't want to start a project just to edit one single Python script, lol, I want to just open a .py file and have It Just Work... Plan 2, I try Komodo 6 Alpha 2. I actually quite like Komodo, and it's nice and snappy, offers in-built Mercurial support, as well as in-built SSH support (although it lacks SSH HTTP Proxy support, which is slightly annoying). However, for some reason, this refuses to pick up Python 3. In Edit-Preferences-Languages, there's two option, one for Python and Python3, but the Python3 one refuses to work, with either the official Python.org binaries, or ActiveState's own ActivePython 3. Of course, I can set the "Python" interpreter to the 3.1 binary, but that's an ugly hack and breaks Python 2.x support. So, does anybody who uses an IDE for Python have any suggestions on either of these accounts, or can you recommend an alternate IDE for Python 3.0 development? Cheers, Victor

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  • How to execute python script on the BaseHTTPSERVER created by python?

    - by user1731699
    I have simply created a python server with : python -m SimpleHTTPServer I had a .htaccess (I don't know if it is usefull with python server) with: AddHandler cgi-script .py Options +ExecCGI Now I am writing a simple python script : #!/usr/bin/python import cgitb cgitb.enable() print 'Content-type: text/html' print ''' <html> <head> <title>My website</title> </head> <body> <p>Here I am</p> </body> </html> ''' I make test.py (name of my script) an executed file with: chmod +x test.py I am launching in firefox with this addres: (http : //) 0.0.0.0:8000/test.py Problem, the script is not executed... I see the code in the web page... And server error is: localhost - - [25/Oct/2012 10:47:12] "GET / HTTP/1.1" 200 - localhost - - [25/Oct/2012 10:47:13] code 404, message File not found localhost - - [25/Oct/2012 10:47:13] "GET /favicon.ico HTTP/1.1" 404 - How can I manage the execution of python code simply? Is it possible to write in a python server to execute the python script like with something like that: import BaseHTTPServer import CGIHTTPServer httpd = BaseHTTPServer.HTTPServer(\ ('localhost', 8123), \ CGIHTTPServer.CGIHTTPRequestHandler) ###  here some code to say, hey please execute python script on the webserver... ;-) httpd.serve_forever() Or something else...

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  • cgi.FieldStorage always empty - never returns POSTed form Data

    - by Dan Carlson
    This problem is probably embarrassingly simple. I'm trying to give python a spin. I thought a good way to start doing that would be to create a simple cgi script to process some form data and do some magic. My python script is executed properly by apache using mod_python, and will print out whatever I want it to print out. My only problem is that cgi.FieldStorage() is always empty. I've tried using both POST and GET. Each trial I fill out both form fields. <form action="pythonScript.py" method="POST" name="ARGH"> <input name="TaskName" type="text" /> <input name="TaskNumber" type="text" /> <input type="submit" /> </form> If I change the form to point to a perl script it reports the form data properly. The python page always gives me the same result: number of keys: 0 #!/usr/bin/python import cgi def index(req): pageContent = """<html><head><title>A page from""" pageContent += """Python</title></head><body>""" form = cgi.FieldStorage() keys = form.keys() keys.sort() pageContent += "<br />number of keys: "+str(len(keys)) for key in keys: pageContent += fieldStorage[ key ].value pageContent += """</body></html>""" return pageContent I'm using Python 2.5.2 and Apache/2.2.3. This is what's in my apache conf file (and my script is in /var/www/python): <Directory /var/www/python/> Options FollowSymLinks +ExecCGI Order allow,deny allow from all AddHandler mod_python .py PythonHandler mod_python.publisher </Directory>

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