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• How do Ruby and Python implement their interactive consoles?

  - by sxa

  When implementing the interpreter for my programming language I first thought of a simple console window which allows the user to enter some code which is then executed as a standalone program as a shell. But there are severe problems: If every line of code the user enters is handled as a standalone program, it has to go through the tokenizer and parser and is then just executed by the interpreter - what about functions then? How can the Python/Ruby interactive consoles (IDLE, irb) "share" the code? How is the code entered handled? Example: >> def x: >> print("Blah") >> >> x() Where is the function stored so it can be called at any time again? How can the interactive console take everything entered as obviously one program without executing everything over and over again?

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• In Python, how to use a C++ function which returns an allocated array of structs via a ** parameter?

  - by Jon-Eric

  I'd like to use some existing C++ code, NvTriStrip, in a Python tool. SWIG easily handles the functions with simple parameters, but the main function, GenerateStrips, is much more complicated. What do I need to put in the SWIG interface file to indicate that primGroups is really an output parameter and that it must be cleaned up with delete[]? /////////////////////////////////////////////////////////////////////////// // GenerateStrips() // // in_indices: input index list, the indices you would use to render // in_numIndices: number of entries in in_indices // primGroups: array of optimized/stripified PrimitiveGroups // numGroups: number of groups returned // // Be sure to call delete[] on the returned primGroups to avoid leaking mem // bool GenerateStrips( const unsigned short* in_indices, const unsigned int in_numIndices, PrimitiveGroup** primGroups, unsigned short* numGroups, bool validateEnabled = false ); FYI, here is the PrimitiveGroup declaration: enum PrimType { PT_LIST, PT_STRIP, PT_FAN }; struct PrimitiveGroup { PrimType type; unsigned int numIndices; unsigned short* indices; PrimitiveGroup() : type(PT_STRIP), numIndices(0), indices(NULL) {} ~PrimitiveGroup() { if(indices) delete[] indices; indices = NULL; } };

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• Queue remote calls to a Python Twisted perspective broker?

  - by agartland

  The strength of Twisted (for python) is its asynchronous framework (I think). I've written an image processing server that takes requests via Perspective Broker. It works great as long as I feed it less than a couple hundred images at a time. However, sometimes it gets spiked with hundreds of images at virtually the same time. Because it tries to process them all concurrently the server crashes. As a solution I'd like to queue up the remote_calls on the server so that it only processes ~100 images at a time. It seems like this might be something that Twisted already does, but I can't seem to find it. Any ideas on how to start implementing this? A point in the right direction? Thanks!

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• How do you get the logical xor of two variables in Python?

  - by Zach Hirsch

  How do you get the logical xor of two variables in Python? For example, I have two variables that I expect to be strings. I want to test that only one of them contains a True value (is not None or the empty string): str1 = raw_input("Enter string one:") str2 = raw_input("Enter string two:") if logical_xor(str1, str2): print "ok" else: print "bad" The ^ operator seems to be bitwise, and not defined on all objects: >>> 1 ^ 1 0 >>> 2 ^ 1 3 >>> "abc" ^ "" Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for ^: 'str' and 'str'

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• Decorators vs. classes in python web development.

  - by Tristan

  I've noticed three main ways Python web frameworks deal request handing: decorators, controller classes with methods for individual requests, and request classes with methods for GET/POST. I'm curious about the virtues of these three approaches. Are there major advantages or disadvantages to any of these approaches? To fix ideas, here are three examples. Bottle uses decorators: @route('/') def index(): return 'Hello World!' Pylons uses controller classes: class HelloController(BaseController): def index(self): return 'Hello World' Tornado uses request handler classes with methods for types: class MainHandler(tornado.web.RequestHandler): def get(self): self.write("Hello, world") Which style is the best practice?

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• How can I import the sqlite3 module into Python 2.4?

  - by Tony

  The sqlite3 module is included in Python version 2.5+. However, I am stuck with version 2.4. I uploaded the sqlite3 module files, added the directory to sys.path, but I get the following error when I try to import it: Traceback (most recent call last): File "<stdin>", line 1, in ? File "sqlite3/__init__.py", line 23, in ? from dbapi2 import * File "sqlite3/dbapi2.py", line 26, in ? from _sqlite3 import * ImportError: No module named _sqlite3 The file '_sqlite3' is in lib-dynload, but if I include this in the sqlite3 directory, I get additional errors. Any suggestions? I am working in a limited environment; I don't have access to GCC, among other things.

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• does adding static library need xcode project of static library for linking?

  - by mirdad

  I have seen some static library projects in iOS.I see two different types of linking static library. 1)adding .a static library to new xcode project and its header files only. 2)adding .a static library to new xcode project and adding the xcode project through which static library has created. when I remove the the xcode project through which static library has created from the 2nd project, it gives error.I tried first approach for 2nd one.But it is not working. Can you please explain why it is differed? Will it be differed by the xcode versions we use? is The second approach for old xcode versions?

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• Python, Matplotlib, subplot: How to set the axis range?

  - by someone

  How can I set the y axis range of the second subplot to e.g. [0,1000] ? The FFT plot of my data (a column in a text file) results in a (inf.?) spike so that the actual data is not visible. pylab.ylim([0,1000]) has no effect, unfortunately. This is the whole script: # based on http://www.swharden.com/blog/2009-01-21-signal-filtering-with-python/ import numpy, scipy, pylab, random xs = [] rawsignal = [] with open("test.dat", 'r') as f: for line in f: if line[0] != '#' and len(line) > 0: xs.append( int( line.split()[0] ) ) rawsignal.append( int( line.split()[1] ) ) h, w = 3, 1 pylab.figure(figsize=(12,9)) pylab.subplots_adjust(hspace=.7) pylab.subplot(h,w,1) pylab.title("Signal") pylab.plot(xs,rawsignal) pylab.subplot(h,w,2) pylab.title("FFT") fft = scipy.fft(rawsignal) #~ pylab.axis([None,None,0,1000]) pylab.ylim([0,1000]) pylab.plot(abs(fft)) pylab.savefig("SIG.png",dpi=200) pylab.show() Other improvements are also appreciated!

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• How can I deploy a Perl/Python/Ruby script without installing an interpreter?

  - by Brian G

  I want to write a piece of software which is essentially a regex data scrubber. I am going to take a contact list in CSV and remove all non-word characters and such from the person's name. This project has Perl written all over it but my client base is largely non-technical and installing Perl on Windows would not be worth it for them. Any ideas on how I can use a Perl/Python/Ruby type language without all the headaches of getting the interpreter on their computer? Thought about web for a second but it would not work for business reasons.

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• How to call a specific, unknown Python object attribute?

  - by Michael Morisy

  I'm working to create a simple Python script that will ultimately tell you how many blog entries were posted in a given month, and the pyblog app is proving very helpful. However, when I create the blog object, I don't know how to access it's various attributes. I can print them all out by printing one item from the dictionary, as shown (in excerpts) below: print blog.get_recent_posts(1) 'post_status': 'publish', 'date_created_gmt': <DateTime '20100601T19:27:17' at 2853300>, 'mt_excerpt': '', 'userid': '288', 'dateCreated': <DateTime '20100601T14:27:17' at 2853350>, 'custom_fields': [{'value': '', 'id': '1317', 'key': 'brightcove_code'}, {'value': 'http://bit.ly/d0Rywl', 'id': '1403', But how can I just get it to provide that DateTime information?

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• how to merge file lines having the same first word in python?

  - by user1377135

  I have written a program to merge lines in a file containing the same first word in python. However I am unable to get the desired output. Can anyone please suggest me the mistake in my program? input "file.txt" line1: a b c line2: a b1 c1 line3: d e f line4: i j k line5: i s t line6: i m n ` output a b c a b1 c1 d e f i j k i s t i m n my code a = [line.split() for line in open('file.txt')] L=[] for i in range(0,len(a)): j=i while True: if a[j][0] == a[j+1][0]: L.append(a[j]) L.append(a[j+1]) j=j+2 else: print a[i] print L break

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• cd Terminal at a given directory after running a Python script?

  - by Dave Everitt

  I'm working on a simple Python script that can use subprocess and/or os to execute some commands, which is working fine. However, when the script exits I'd like to cd the actual Terminal (in this case OS X) so on exit, the new files are ready to use in the directory where the have been created. All the following (subprocess.Popen, os.system, os.chdir) can do what I want from within the script (i.e. they execute stuff in the target directory) but on exit leave the Terminal at the script's own directory, not the target directory. I'd like to avoid writing a shell script to temporary file just to achieve this, if this is at all possible anyway?

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• [LINQ noob] Please help me convert this Python 3.x snippet to .net LINQ.

  - by Hamish Grubijan

  I want to sort elements of a HashSet<string> and join them by a ; character. Python interpreter version: >>> st = {'jhg', 'uywer', 'nbcm', 'utr'} >>> strng = ';'.join(sorted(s)) >>> strng 'ASD;anmbh;ashgg;jhghjg' C# signature of a method I seek: private string getVersionsSorted(HashSet<string> versions); I can do this without using Linq, but I really want to learn it better. Many thanks!

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• Java or Python distributed compute job (on a student budget)?

  - by midget_sadhu

  I have a large dataset (c. 40G) that I want to use for some NLP (largely embarrassingly parallel) over a couple of computers in the lab, to which i do not have root access, and only 1G of user space. I experimented with hadoop, but of course this was dead in the water-- the data is stored on an external usb hard drive, and i cant load it on to the dfs because of the 1G user space cap. I have been looking into a couple of python based options (as I'd rather use NLTK instead of Java's lingpipe if I can help it), and it seems distributed compute options look like: Ipython DISCO After my hadoop experience, i am trying to make sure i try and make an informed choice -- any help on what might be more appropriate would be greatly appreciated. Amazon's EC2 etc not really an option, as i have next to no budget.

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• idiomatic way to take groups of n items from a list in Python?

  - by Wang

  Given a list A = [1 2 3 4 5 6] Is there any idiomatic (Pythonic) way to iterate over it as though it were B = [(1, 2) (3, 4) (5, 6)] other than indexing? That feels like a holdover from C: for a1,a2 in [ (A[i], A[i+1]) for i in range(0, len(A), 2) ]: I can't help but feel there should be some clever hack using itertools or slicing or something. (Of course, two at a time is just an example; I'd like a solution that works for any n.) Edit: related http://stackoverflow.com/questions/1162592/iterate-over-a-string-2-or-n-characters-at-a-time-in-python but even the cleanest solution (accepted, using zip) doesn't generalize well to higher n without a list comprehension and *-notation.

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• What's the most scalable way to handle somewhat large file uploads in a Python webapp?

  - by Jason Baker

  We have a web application that takes file uploads for some parts. The file uploads aren't terribly big (mostly word documents and such), but they're much larger than your typical web request and they tend to tie up our threaded servers (zope 2 servers running behind an Apache proxy). I'm mostly in the brainstorming phase right now and trying to figure out a general technique to use. Some ideas I have are: Using a python asynchronous server like tornado or diesel or gunicorn. Writing something in twisted to handle it. Just using nginx to handle the actual file uploads. It's surprisingly difficult to find information on which approach I should be taking. I'm sure there are plenty of details that would be needed to make an actual decision, but I'm more worried about figuring out how to make this decision than anything else. Can anyone give me some advice about how to proceed with this?

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• Asking for input without stopping the script in python.

  - by ImTooStupidForThis

  I am (trying) to make a simple IRC client in python (as kind of a project while I learn the language). I have a loop that I use to receive and parse what the IRC server sends me, but if I use raw_input to input stuff, it stops the loop dead in its tracks until I input something (obviously). How can I input something without the loop stopping? Thanks in advance. (I don´t think I need to post the code, I just want to input something without the while 1 loop stopping.)

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• Python - Flatten a dict of lists into unique values?

  - by Jonathan Vanasco

  I have a dict of lists in python: content = {88962: [80, 130], 87484: [64], 53662: [58,80]} I want to turn it into a list of the unique values [58,64,80,130] I wrote a manual solution, but it's a manual solution. I know there are more concise and more elegant way to do this with list comprehensions, map/reduce , itertools , etc. anyone have a clue ? content = {88962: [80, 130], 87484: [64], 53662: [58,80]} result = set({}) for k in content.keys() : for i in content[k]: result.add(i) # and list/sort/print just to compare the output r2 = list( result ) r2.sort() print r2

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• Python - what's your conventions to declare your attributes in a class ?

  - by SeyZ

  Hello, In Python, I can declare attributes all over the class. For example : class Foo: def __init__(self): self.a = 0 def foo(self): self.b = 0 It's difficult to retrieve all attributes in my class when I have a big class with a lot of attributes. Is it better to have the following code (a) or the next following code (b) : a) Here, it's difficult to locate all attributes : class Foo: def __init__(self): foo_1() foo_2() def foo_1(self): self.a = 0 self.b = 0 def foo_2(self): self.c = 0 b) Here, it's easy to locate all attributes but is it beautiful ? class Foo: def __init__(self): (self.a, self.b) = foo_1() self.c = foo_2() def foo_1(self): a = 0 b = 0 return (a, b) def foo_2(self): c = 0 return c In a nutshell, what is your conventions to declare your attributes in a class ?

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• Python: How To copy function parameters into object's fields effortlessly ?

  - by bandana

  Many times I have member functions that copy parameters into object's fields. For Example: class NouveauRiches(object): def __init__(self, car, mansion, jet, bling): self.car = car self.mansion = mansion self.jet = jet self.bling = bling Is there a python language construct that would make the above code less tedious? One could use *args: def __init__(self, *args): self.car, self.mansion, self.jet, self.bling = args +: less tedious -: function signature not revealing enough. need to dive into function code to know how to use function -: does not raise a TypeError on call with wrong # of parameters (but does raise a ValueError) Any other ideas? (Whatever your suggestion, make sure the code calling the function does stays simple)

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• Why doesn't Python's `re.split()` split on zero-length matches?

  - by Tim Pietzcker

  One particular quirk of the (otherwise quite powerful) re module in Python is that re.split() will never split a string on a zero-length match, for example if I want to split a string along word boundaries: >>> re.split(r"\s+|\b", "Split along words, preserve punctuation!") ['Split', 'along', 'words,', 'preserve', 'punctuation!'] instead of ['', 'Split', 'along', 'words', ',', 'preserve', 'punctuation', '!'] Why does it have this limitation? Is it by design? Do other regex flavors behave like this?

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• How do I change my current directory from a python script?

  - by misterloogs

  I'm trying to implement my own version of the 'cd' command that presents the user with a list of hard-coded directories to choose from, and the user has to enter a number corresponding to an entry in the list. The program, named my_cd.py for now, should then effectively 'cd' the user to the chosen directory. Example of how this should work: /some/directory $ my_cd.py 1) ~ 2) /bin/ 3) /usr Enter menu selection, or q to quit: 2 /bin $ Currently, I'm trying to 'cd' using os.chdir('dir'). However, this doesn't work, probably because my_cd.py is kicked off in its own child process. I tried wrapping the call to my_cd.py in a sourced bash script named my_cd.sh: #! /bin/bash function my_cd() { /path/to/my_cd.py } /some/directory $ . my_cd.sh $ my_cd ... shows list of dirs, but doesn't 'cd' in the interactive shell Any ideas on how I can get this to work? Is it possible to change my interactive shell's current directory from a python script?

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• Whats the python way for recursively setting file permissions?

  - by Geoff

  What's the "python way" to recursively set the owner and group to files in a directory? I could just pass a 'chown -R' command to shell, but I feel like I'm missing something obvious. I'm mucking about with this: import os path = "/tmp/foo" for root, dirs, files in os.walk(path): for momo in dirs: os.chown(momo, 502, 20) This seems to work for setting the directory, but fails when applied to files. I suspect the files are not getting the whole path, so chown fails since it can't find the files. The error is: 'OSError: [Errno 2] No such file or directory: 'foo.html' What am I overlooking here?

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• Is it inefficient to access a python class member container in a loop statement?

  - by Dave

  Hi there. I'm trying to adopt some best practices to keep my python code efficient. I've heard that accessing a member variable inside of a loop can incur a dictionary lookup for every iteration of the loop, so I cache these in local variables to use inside the loop. My question is about the loop statement itself... if I have the following class: class A(object): def init(self) self.myList = [ 'a','b','c', 'd', 'e' ] Does the following code in a member function incur one, or one-per-loop-iteration (5) dictionary lookups? for letter in self.myList: print letter IE, should I adopt the following pattern, if I am concerned about efficiency... localList = self.myList for letter in localList: print letter or is that actually LESS efficient due to the local variable assign? Note, I am aware that early optimization is a dangerous pitfall if I'm concerned about the overall efficiency of code development. Here I am specifically asking about the efficiency of the code, not the coding. Thanks in advance! D

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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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