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• Is there an equivalent in Scala to Python's more general map function?

  - by wheaties

  I know that Scala's Lists have a map implementation with signature (f: (A) => B):List[B] and a foreach implementation with signature (f: (A) => Unit):Unit but I'm looking for something that accepts multiple iterables the same way that the Python map accepts multiple iterables. I'm looking for something with a signature of (f: (A,B) => C, Iterable[A], Iterable[B] ):Iterable[C] or equivalent. Is there a library where this exists or a comparable way of doing similar?

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• What is your strategy to avoid dynamic typing errors in Python (NoneType has not attribute x)?

  - by Koen Bok

  Python is one of my favorite languages, but I really have a love/hate relationship with it's dynamicness. Apart from the advantages, it often results in me forgetting to check a type, trying to call an attribute and getting the NoneType (or any other) has no attribute x error. A lot of them are pretty harmless but if not handled correctly they can bring down your entire app/process/etc. Over time I got better predicting where these could pop up and adding explicit type checking, but because I'm only human I miss one occasionally and then some end-user finds it. So I'm interested in your strategy to avoid these. Do you use type-checking decorators? Maybe special object wrappers? Please share...

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• how to work with strings and integers as bit strings in python?

  - by Manuel

  Hello! I'm developing a Genetic Algorithm in python were chromosomes are composed of strings and integers. To apply the genetic operations, I want to convert these groups of integers and strings into bit strings. For example, if one chromosome is: ["Hello", 4, "anotherString"] I'd like it to become something like: 0100100100101001010011110011 (this is not actual translation). So... How can I do this? Chromosomes will contain the same amount of strings and integers, but this numbers can vary from one algorithm run to another. To be clear, what I want to obtain is the bit representation of each element in the chromosome concatenated. If you think this would not be the best way to apply genetic operators (such as mutation and simple crossover) just tell me! I'm open to new ideas. Thanks a lot! Manuel

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• How can I skip the current item and the next in a Python loop?

  - by uberjumper

  This might be a really dumb question, however I've looked around online, etc. And have not seen a solid answer. Is there a simple way to do something like this? lines = open('something.txt', 'r').readlines() for line in lines: if line == '!': # force iteration forward twice line.next().next() <etc> It's easy to do in C++; just increment the iterator an extra time. Is there an easy way to do that in Python? I would just like to point, out the main purpose of this question is not about "reading files and such" and skipping things. I was more looking for C++ iterator style iteration. Also the new title is kinda dumb, and i dont really think it reflects the nature of my question.

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• Is there anything for Python that is like readability.js?

  - by Emre Sevinç

  Hi, I'm looking for a package / module / function etc. that is approximately the Python equivalent of Arc90's readability.js http://lab.arc90.com/experiments/readability http://lab.arc90.com/experiments/readability/js/readability.js so that I can give it some input.html and the result is cleaned up version of that html page's "main text". I want this so that I can use it on the server-side (unlike the JS version that runs only on browser side). Any ideas? PS: I have tried Rhino + env.js and that combination works but the performance is unacceptable it takes minutes to clean up most of the html content :( (still couldn't find why there is such a big performance difference).

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• How to parse strings representing xml.dom.minidom nodes in python?

  - by Francis Davey

  I have a collection of nodes xml.dom.Node objects created using xml.dom.minidom. I store them (individually) in a database by converting them to a string using the toxml() method of a the Node object. The problem is that I'd sometimes like to be able to convert them back to the appropriate Node object using a parser of some kind. As far as I can see the various libraries shipped with python use Expat which won't parse a string like '' or indeed anything which is not a correct xml string. So, does anyone have any ideas? I realise I could pickle the nodes in some way and then unpickle them, but that feels unpleasant and I'd much rather be storing in a form I can read for maintenance purposes. Surely there is something that will do this?

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• Can I use an opened gzip file with Popen in Python?

  - by eric.frederich

  I have a little command line tool that reads from stdin. On the command line I would run either... ./foo < bar or ... cat bar | ./foo With a gziped file I can run zcat bar.gz | ./foo in Python I can do ... Popen(["./foo", ], stdin=open('bar'), stdout=PIPE, stderr=PIPE) but I can't do import gzip Popen(["./foo", ], stdin=gzip.open('bar'), stdout=PIPE, stderr=PIPE) I wind up having to run p0 = Popen(["zcat", "bar"], stdout=PIPE, stderr=PIPE) Popen(["./foo", ], stdin=p0.stdout, stdout=PIPE, stderr=PIPE) Am I doing something wrong? Why can't I use gzip.open('bar') as an stdin arg to Popen?

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• How to find the mime type of a file in python?

  - by Daren Thomas

  Let's say you want to save a bunch of files somewhere, for instance in BLOBs. Let's say you want to dish these files out via a web page and have the client automatically open the correct application/viewer. Assumption: The browser figures out which application/viewer to use by the mime-type (content-type?) header in the HTTP response. Based on that assumption, in addition to the bytes of the file, you also want to save the MIME type. How would you find the MIME type of a file? I'm currently on a Mac, but this should also work on Windows. Does the browser add this information when posting the file to the web page? Is there a neat python library for finding this information? A WebService or (even better) a downloadable database? Edit: Thank you, Dave Webb.

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• Why can't I get Python's urlopen() method to work?

  - by froadie

  Why isn't this simple Python code working? import urllib file = urllib.urlopen('http://www.google.com') print file.read() This is the error that I get: Traceback (most recent call last): File "C:\workspace\GarchUpdate\src\Practice.py", line 26, in <module> file = urllib.urlopen('http://www.google.com') File "C:\Python26\lib\urllib.py", line 87, in urlopen return opener.open(url) File "C:\Python26\lib\urllib.py", line 206, in open return getattr(self, name)(url) File "C:\Python26\lib\urllib.py", line 345, in open_http h.endheaders() File "C:\Python26\lib\httplib.py", line 892, in endheaders self._send_output() File "C:\Python26\lib\httplib.py", line 764, in _send_output self.send(msg) File "C:\Python26\lib\httplib.py", line 723, in send self.connect() File "C:\Python26\lib\httplib.py", line 704, in connect self.timeout) File "C:\Python26\lib\socket.py", line 514, in create_connection raise error, msg IOError: [Errno socket error] [Errno 10060] A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond I've tried it with several different pages but I can never get the urlopen method to execute correctly.

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• how i can open different linux terminal to output differnt kinds of debug information in python?

  - by Registered User KC

  Hi All, I need output different information to different terminal instances instead of print them in same output stream, say std.err or std.out. for example: I have 5 kinds of information say A-E need to be displayed on different terminal windows on same desktop, looks like [terminal 1] <- for displaying information A [terminal 2] <- for displaying information B [terminal 3] <- for displaying information C [terminal 4] <- for displaying information D [terminal 5] <- for displaying information E I know I can output them into different files, then open terminals read the file in loop, but what I want is python program can open terminal by program itself and print to them directly when it is needed. Is it possible? Thanks! KC

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• Python: does it make sense to refactor this check into it's own method?

  - by Jeff Fry

  I'm still learning python. I just wrote this method to determine if a player has won a game of tic-tac-toe yet, given a board state like:'[['o','x','x'],['x','o','-'],['x','o','o']]' def hasWon(board): players = ['x', 'o'] for player in players: for row in board: if row.count(player) == 3: return player top, mid, low = board for i in range(3): if [ top[i],mid[i],low[i] ].count(player) == 3: return player if [top[0],mid[1],low[2]].count(player) == 3: return player if [top[2],mid[1],low[0]].count(player) == 3: return player return None It occurred to me that I check lists of 3 chars several times and could refactor the checking to its own method like so: def check(list, player): if list.count(player) == 3: return player ...but then realized that all that really does is change lines like: if [ top[i],mid[i],low[i] ].count(player) == 3: return player to: if check( [top[i],mid[i],low[i]], player ): return player ...which frankly doesn't seem like much of an improvement. Do you see a better way to refactor this? Or in general a more Pythonic option? I'd love to hear it!

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• Accessing a dictionary value by custom object value in Python?

  - by Sam

  So I have a square that's made up of a series of points. At every point there is a corresponding value. What I want to do is build a dictionary like this: class Point: def __init__(self, x, y): self._x = x self._y = y square = {} for x in range(0, 5): for y in range(0, 5): point = Point(x,y) square[point] = None However, if I later create a new point object and try to access the value of the dictionary with the key of that point it doesn't work.. square[Point(2,2)] Traceback (most recent call last): File "<pyshell#19>", line 1, in <module> square[Point(2,2)] KeyError: <__main__.Point instance at 0x02E6C378> I'm guessing that this is because python doesn't consider two objects with the same properties to be the same object? Is there any way around this? Thanks

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• python optparse, how to include additional info in usage output?

  - by CarpeNoctem

  Using python's optparse module I would like to add extra example lines below the regular usage output. My current help_print() output looks like this: usage: check_dell.py [options] options: -h, --help show this help message and exit -s, --storage checks virtual and physical disks -c, --chassis checks specified chassis components I would like it to include usage examples for the less *nix literate users at my work. Something like this: usage: check_dell.py [options] options: -h, --help show this help message and exit -s, --storage checks virtual and physical disks -c, --chassis checks specified chassis components Examples: check_dell -c all check_dell -c fans memory voltage check_dell -s How would I accomplish this? What optparse options allow for such? Current code: import optparse def main(): parser = optparse.OptionParser() parser.add_option('-s', '--storage', action='store_true', default=False, help='checks virtual and physical disks') parser.add_option('-c', '--chassis', action='store_true', default=False, help='checks specified chassis components') (opts, args) = parser.parse_args()

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• Find out 20th, 30th, nth prime number. (I'm getting 20th but not 30th?) [Python]

  - by gsin

  The question is to find the 1000th prime number. I wrote the following python code for this. The problem is, I get the right answer for the 10th , 20th prime but after that each increment of 10 leaves me one off the mark. I can't catch the bug here :( count=1 #to keep count of prime numbers primes=() #tuple to hold primes candidate=3 #variable to test for primes while count<20: for x in range(2,candidate): if candidate%x==0: candidate=candidate+2 else : pass primes=primes+(candidate,) candidate=candidate+2 count=count+1 print primes print "20th prime is ", primes[-1] In case you're wondering, count is initialised as 1 because I am not testing for 2 as a prime number(I'm starting from 3) and candidate is being incremented by 2 because only odd numbers can be prime numbers. I know there are other ways of solving this problem, such as the prime number theorem but I wanna know what's wrong with this approach. Also if there are any optimisations you have in mind, please suggest. Thank You

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• How do I find out if the variable is declared in Python?

  - by golergka

  I want to use a module as a singleton referenced in other modules. It looks something like this (that's not actually a code I'm working on, but I simplified it to throw away all unrelated stuff): main.py import singleton import printer def main(): singleton.Init(1,2) printer.Print() if __name__ == '__main__': pass singleton.py variable1 = '' variable2 = '' def Init(var1, var2) variable1 = var1 variable2 = var2 printer.py import singleton def Print() print singleton.variable1 print singleton.variable2 I expect to get output 1/2, but instead get empty space. I understand that after I imported singleton to the print.py module the variables got initialized again. So I think that I must check if they were intialized before in singleton.py: if not (variable1): variable1 = '' if not (variable2) variable2 = '' But I don't know how to do that. Or there is a better way to use singleton modules in python that I'm not aware of :)

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• Python del() built-in can't be used in assignment?

  - by emcee

  I noticed a problem when I was trying to use del in a lambda to thin out a list of threads to just those running: map(lambda x: del(x) if not x.isAlive() else x, self.threads) Ignore for a second that this doesn't do anything, I'm just fooling around with map, reduce, and lambda. This fails with a syntax error at del(x). With some messing around, I think the problem is del() doesn't return a value. For example, this fails with the same error: b = 5 x = del(b) This doesn't, however: def rmThis(x): del(x) Which means I'm using this workaround: map(lambda x: rmThis(x) if not x.isAlive() else x, self.threads) So is the limitation just because del() doesn't return a value? Why not? I'm using python 2.6.2

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• Python file input string: how to handle escaped unicode characters?

  - by Michi

  In a text file (test.txt), my string looks like this: Gro\u00DFbritannien Reading it, python escapes the backslash: >>> file = open('test.txt', 'r') >>> input = file.readline() >>> input 'Gro\\u00DFbritannien' How can I have this interpreted as unicode? decode() and unicode() won't do the job. The following code writes Gro\u00DFbritannien back to the file, but I want it to be Großbritannien >>> input.decode('latin-1') u'Gro\\u00DFbritannien' >>> out = codecs.open('out.txt', 'w', 'utf-8') >>> out.write(input)

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• Why doesn't negative values for the second index in a jagged array work in Python?

  - by univerio

  For example, if I have the following (data from Project Euler): s = [[75], [95, 64], [17, 47, 82], [18, 35, 87, 10], [20, 4, 82, 47, 65], [19, 1, 23, 75, 3, 34], [88, 2, 77, 73, 7, 63, 67], [99, 65, 4, 28, 6, 16, 70, 92], [41, 41, 26, 56, 83, 40, 80, 70, 33], [41, 48, 72, 33, 47, 32, 37, 16, 94, 29], [53, 71, 44, 65, 25, 43, 91, 52, 97, 51, 14], [70, 11, 33, 28, 77, 73, 17, 78, 39, 68, 17, 57], [91, 71, 52, 38, 17, 14, 91, 43, 58, 50, 27, 29, 48], [63, 66, 4, 68,89, 53, 67, 30, 73, 16, 69, 87, 40, 31], [4, 62, 98, 27, 23, 9, 70, 98, 73, 93, 38, 53, 60, 4, 23]] Why does s[1:][:-1] give me the same thing as s[1:] instead of (what I want) [s[i][:-1] for i in range(1,len(s))]. In other words, why does Python ignore my second index?

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• How do I configure the Python logging module in Django?

  - by mipadi

  I'm trying to configure logging for a Django app using the Python logging module. I have placed the following bit of configuration code in my Django project's settings.py file: import logging import logging.handlers import os date_fmt = '%m/%d/%Y %H:%M:%S' log_formatter = logging.Formatter(u'[%(asctime)s] %(levelname)-7s: %(message)s (%(filename)s:%(lineno)d)', datefmt=date_fmt) log_dir = os.path.join(PROJECT_DIR, "var", "log", "my_app") log_name = os.path.join(log_dir, "nyrb.log") bytes = 1024 * 1024 # 1 MB if not os.path.exists(log_dir): os.makedirs(log_dir) handler = logging.handlers.RotatingFileHandler(log_name, maxBytes=bytes, backupCount=7) handler.setFormatter(log_formatter) handler.setLevel(logging.DEBUG) logging.getLogger().setLevel(logging.DEBUG) logging.getLogger().addHandler(handler) logging.getLogger(__name__).info("Initialized logging subsystem") At startup, I get a couple Django-related messages, as well as the "Initialized logging subsystem", in the log files, but then all the log messages end up going to the web server logs (/var/log/apache2/error.log, since I'm using Apache), and use the standard log format (not the formatter I designated). Am I configuring logging incorrectly?

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• How can I set Invitee in Google Calendar through Python?

  - by Dhaval dave

  I am Setting Google Calendar via python command like this def _InsertQuickAddEvent(self, content="Tennis with dddddd on 5/19/2010 4am-5:30am"): """Creates an event with the quick_add property set to true so the content is processed as quick add content instead of as an event description.""" event = gdata.calendar.CalendarEventEntry() who = whois("[email protected]") event.content = atom.Content(text=content) event.quick_add = gdata.calendar.QuickAdd(value='true'); new_event = self.cal_client.InsertEvent(event, '/calendar/feeds/default/private/full') return new_event this code is given by Google API Can any one suggest what to do to add invitee in this? Important links for that http://code.google.com/apis/calendar/data/1.0/developers_guide_python.html

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• What's the right way to use idlestartup on python 2.6.5?

  - by user210481

  Idlestartup is analogous to pythonstartup variable, but for IDLE, instead of command line. But it seems not to work properly. I'm using python 2.6.5 on Windows. I have the following script assigned to it: from pprint import pprint import sys newPath = 'C:\\Python26\test') sys.path.append(newPath) print "initial config loaded" Both variables Idlestartup and pythonstartup are assigned to the same file (script above). When running IDLE, pprint and sys are NOT available, the final message is NOT printed, but newPath was added to sys.path. Running the command line, pprint and sys are available, the final message is printed and newPath was added to sys.path. Is it a bug? Am I doing something wrong? Thanks

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• Can I add custom methods/attributes to built-in Python types?

  - by sfjedi

  For example—say I want to add a helloWorld() method to Python's dict type. Can I do this? JavaScript has a prototype object that behaves this way. Maybe it's bad design and I should subclass the dict object, but then it only works on the subclasses and I want it to work on any and all future dictionaries. Here's how it would go down in JavaScript: String.prototype.hello = function() { alert("Hello, " + this + "!"); } "Jed".hello() //alerts "Hello, Jed!" Here's a useful link with more examples— http://www.javascriptkit.com/javatutors/proto3.shtml

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• Error while trying to parse a website url using python . how to debug it ?

  - by mekasperasky

  #!/usr/bin/python import json import urllib from BeautifulSoup import BeautifulSoup from BeautifulSoup import BeautifulStoneSoup import BeautifulSoup def showsome(searchfor): query = urllib.urlencode({'q': searchfor}) url = 'http://ajax.googleapis.com/ajax/services/search/web?v=1.0&%s' % query search_response = urllib.urlopen(url) search_results = search_response.read() results = json.loads(search_results) data = results['responseData'] print 'Total results: %s' % data['cursor']['estimatedResultCount'] hits = data['results'] print 'Top %d hits:' % len(hits) for h in hits: print ' ', h['url'] resp = urllib.urlopen(h['url']) res = resp.read() soup = BeautifulSoup(res) print soup.prettify() print 'For more results, see %s' % data['cursor']['moreResultsUrl'] showsome('sachin') What is the wrong in this code ? Note all the 4 links that I am getting out of the search , I am feeding it back to extract the contents out of it , and then use BeautifulSoup to parse it . How should I go about it ?

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• How to display a PostScript file in a Python GUI application.

  - by Mike Graham

  I would like to build a cross-platform GUI application in Python that displays PostScript files I generate, among some other stuff. What is the best way to accomplish this? Ideally I would be able to do things like zoom and pan the displayed graphic. Do any/some/all of the GUI toolkits have something I can drop in to do this, and if so what are they called and how do they work? If necessary, I can convert the postscript file to PDF or a raster format behind the scenes, but I'd rather not do the latter.

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• Python: How do I pass a variable by reference?

  - by David Sykes

  The Python documentation seems unclear about whether parameters are passed by reference or value, and the following code produces the unchanged value 'Original' class PassByReference: def __init__(self): self.variable = 'Original' self.Change(self.variable) print self.variable def Change(self, var): var = 'Changed' Is there something I can do to pass the variable by actual reference? Update: I am coming to the conclusion that while Andrea answered my actual question (Can you... No but you can...), on the subject of pass by reference Blair Conrad is more technically correct. As I understand it the crux is that a copy of a reference is being passed. If you assign that copy, as in my example, then you lose the reference to the original and it remains unchanged. If, however, you 'use' that reference, for example append on a passed list, then the original is changed. I will see how the comments and votes go before choosing the answer people think is the best

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