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  • Python nested dict comprehension with sets

    - by Jasie
    Can someone explain how to do nested dict comprehensions? >> l = [set([1, 2, 3]), set([4, 5, 6])] >> j = dict((a, i) for a in s for i, s in enumerate(l)) >> NameError: name 's' is not defined I would have liked: >> j >> {1:0, 2:0, 3:0, 4: 1, 5: 1, 6: 1} I just asked a previous question about a simpler dict comprehension where the parentheses in the generator function were reduced. How come the s in the leftmost comprehension is not recognized?

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  • Dynamic dispatch and inheritance in python

    - by Bill Zimmerman
    Hi, I'm trying to modify Guido's multimethod (dynamic dispatch code): http://www.artima.com/weblogs/viewpost.jsp?thread=101605 to handle inheritance and possibly out of order arguments. e.g. (inheritance problem) class A(object): pass class B(A): pass @multimethod(A,A) def foo(arg1,arg2): print 'works' foo(A(),A()) #works foo(A(),B()) #fails Is there a better way than iteratively checking for the super() of each item until one is found? e.g. (argument ordering problem) I was thinking of this from a collision detection standpoint. e.g. foo(Car(),Truck()) and foo(Truck(), Car()) and should both trigger foo(Car,Truck) # Note: @multimethod(Truck,Car) will throw an exception if @multimethod(Car,Truck) was registered first? I'm looking specifically for an 'elegant' solution. I know that I could just brute force my way through all the possibilities, but I'm trying to avoid that. I just wanted to get some input/ideas before sitting down and pounding out a solution. Thanks

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  • Working with multiple input and output files in Python

    - by Morlock
    I need to open multiple files (2 input and 2 output files), do complex manipulations on the lines from input files and then append results at the end of 2 output files. I am currently using the following approach: in_1 = open(input_1) in_2 = open(input_2) out_1 = open(output_1, "w") out_2 = open(output_2, "w") # Read one line from each 'in_' file # Do many operations on the DNA sequences included in the input files # Append one line to each 'out_' file in_1.close() in_2.close() out_1.close() out_2.close() The files are huge (each potentially approaching 1Go, that is why I am reading through these input files one at a time. I am guessing that this is not a very Pythonic way to do things. :) Would using the following form good? with open("file1") as f1: with open("file2") as f2: # etc. If yes, could I do it while avoiding the highly indented code that would result? Thanks for the insights!

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  • Python datetime to Unix timestamp

    - by Off Rhoden
    I have to create an "Expires" value 5 minutes in the future, but I have to supply it in UNIX Timestamp format. I have this so far, but it seems like a hack. def expires(): '''return a UNIX style timestamp representing 5 minutes from now''' epoch = datetime.datetime(1970, 1, 1) seconds_in_a_day = 60 * 60 * 24 five_minutes = datetime.timedelta(seconds=5*60) five_minutes_from_now = datetime.datetime.now() + five_minutes since_epoch = five_minutes_from_now - epoch return since_epoch.days * seconds_in_a_day + since_epoch.seconds Is there a module or function that does the timestamp conversion for me?

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  • Take the intersection of an arbitrary number of lists in python

    - by thepandaatemyface
    Suppose I have a list of lists of elements which are all the same (i'll use ints in this example) [range(100)[::4], range(100)[::3], range(100)[::2], range(100)[::1]] What would be a nice and/or efficient way to take the intersection of these lists (so you would get every element that is in each of the lists)? For the example that would be: [0, 12, 24, 36, 48, 60, 72, 84, 96]

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  • Small Python optional arguments question

    - by ooboo
    I have two functions: def f(a,b,c=g(b)): blabla def g(n): blabla c is an optional argument in function f. If the user does not specify its value, the program should compute g(b) and that would be the value of c. But the code does not compile - it says name 'b' is not defined. How to fix that? Someone suggested: def g(b): blabla def f(a,b,c=None): if c is None: c = g(b) blabla But this doesn't work, because maybe the user intended c to be None and then c will have another value.

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  • How do I calculate percentiles with python/numpy?

    - by Uri
    Is there a convenient way to calculate percentiles for a sequence or single-dimensional numpy array? I am looking for something similar to Excel's percentile function. I looked in NumPy's statistics reference, and couldn't find this. All I could find is the median (50th percentile), but not something more specific.

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  • Google App Engine python - Self is not defined

    - by sdasdas
    I have a request that maps to this class ChatMsg It takes in 3 get variables, username, roomname, and msg. But it fails on this last line here. class ChatMsg(webapp.RequestHandler): # this is line 239 def get(self): username = urllib.unquote(self.request.get('username')) roomname = urllib.unquote(self.request.get('roomname')) # this is line 242 When it tries to assign roomname, it tells me: <type 'exceptions.NameError'>: name 'self' is not defined Traceback (most recent call last): File "/base/data/home/apps/chatboxes/1.341998073649951735/chatroom.py", line 239, in <module> class ChatMsg(webapp.RequestHandler): File "/base/data/home/apps/chatboxes/1.341998073649951735/chatroom.py", line 242, in ChatMsg roomname = urllib.unquote(self.request.get('roomname')) what the hell is going on to make self not defined

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  • Python ctypes argument errors

    - by Patrick Moriarty
    Hello. I wrote a test dll in C++ to make sure things work before I start using a more important dll that I need. Basically it takes two doubles and adds them, then returns the result. I've been playing around and with other test functions I've gotten returns to work, I just can't pass an argument due to errors. My code is: import ctypes import string nDLL = ctypes.WinDLL('test.dll') func = nDLL['haloshg_add'] func.restype = ctypes.c_double func.argtypes = (ctypes.c_double,ctypes.c_double) print(func(5.0,5.0)) It returns the error for the line that called "func": ValueError: Procedure probably called with too many arguments (8 bytes in excess) What am I doing wrong? Thanks.

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  • Parsing text file in python

    - by Ockonal
    Hello, I have html-file. I have to replace all text between this: [%anytext%]. As I understand, it's very easy to do with BeautifulSoup for parsing hmtl. But what is regular expression and how to remove&write back text data?

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  • python threading and performace?

    - by kumar
    I had to do heavy I/o bound operation, i.e Parsing large files and converting from one format to other format. Initially I used to do it serially, i.e parsing one after another..! Performance was very poor ( it used take 90+ seconds). So I decided to use threading to improve the performance. I created one thread for each file. ( 4 threads) for file in file_list: t=threading.Thread(target = self.convertfile,args = file) t.start() ts.append(t) for t in ts: t.join() But for my astonishment, there is no performance improvement whatsoever. Now also it takes around 90+ seconds to complete the task. As this is I/o bound operation , I had expected to improve the performance. What am I doing wrong?

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  • Python modify an xml file

    - by michele
    I have this xml model. link text So I have to add some node (see the text commented) to this file. How I can do it? I have writed this partial code but it doesn't work: xmldoc=minidom.parse(directory) child = xmldoc.createElement("map") for node in xmldoc.getElementsByTagName("Environment"): node.appendChild(child) Thanks in advance.

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  • How to loop over nodes with xmlfeed using scrapy python

    - by Kour ipm
    Hi i working on scrapy and trying xml feeds first time, below is my code class TestxmlItemSpider(XMLFeedSpider): name = "TestxmlItem" allowed_domains = {"http://www.nasinteractive.com"} start_urls = [ "http://www.nasinteractive.com/jobexport/advance/hcantexasexport.xml" ] iterator = 'iternodes' itertag = 'job' def parse_node(self, response, node): title = node.select('title/text()').extract() job_code = node.select('job-code/text()').extract() detail_url = node.select('detail-url/text()').extract() category = node.select('job-category/text()').extract() print title,";;;;;;;;;;;;;;;;;;;;;" print job_code,";;;;;;;;;;;;;;;;;;;;;" item = TestxmlItem() item['title'] = node.select('title/text()').extract() ....... return item result: File "/usr/lib/python2.7/site-packages/Scrapy-0.14.3-py2.7.egg/scrapy/item.py", line 56, in __setitem__ (self.__class__.__name__, key)) exceptions.KeyError: 'TestxmlItem does not support field: title' Totally there are 200+ items so i need to loop over and assign the node text to item but here all the results are displaying at once when we print, actually how can we loop over on nodes in scraping xml files with xmlfeedspider

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  • Youtube python: get thumbnail

    - by dkgirl
    Is there a simple way to get the default thumbnail from a youtube entry object gdata.youtube.YouTubeVideoEntry? I tried entry.media.thumbnail, but that gives me four thumbnail objects. Can I always trust that there are four? Can I know which is the default thumbnail that would also appears on the youtube search page? And how would I get that one? Or do I have to alter one of the other ones? When I know the video_id I use: http://i4.ytimg.com/vi/{{video_id}}/default.jpg so, it would also be helpful to get the video_id. Do I really have to parse one of the url's to get at the video_id ? It seems strange that they don't provide this information directly.

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  • sorting content of a text file in python

    - by rabidmachine9
    I have this small script that sorts the content of a text file # The built-in function `open` opens a file and returns a file object. # Read mode opens a file for reading only. try: f = open("tracks.txt", "r") try: # Read the entire contents of a file at once. # string = f.read() # OR read one line at a time. #line = f.readline() # OR read all the lines into a list. lines = f.readlines() lines.sort() f = open('tracks.txt', 'w') f.writelines(lines) # Write a sequence of strings to a file finally: f.close() except IOError: pass the only problem is that the text is displayed at the bottom of the text file everytime it's sortened... I assume it also sorts the blank lines...anybody knows why? thanks in advance

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  • Redirect print in Python: val = print(arg) to output mixed iterable to file

    - by emcee
    So lets say I have an incredibly nested iterable of lists/dictionaries. I would like to print them to a file as easily as possible. Why can't I just redirect print to a file? val = print(arg) gets a SyntaxError. Is there a way to access stdinput? And why does print take forever with massive strings? Bad programming on my side for outputting massive strings, but quick debugging--and isn't that leveraging the strength of an interactive prompt? There's probably also an easier way than my gripe. Has the hive-mind an answer?

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  • ListCtrl - wxPython / Python

    - by Francisco Aleixo
    Hello everyone. My question is if we can assign/bind some value to a certain item and hide that value(or if we can do the same thing in another way). Example: Lets say the columns on ListCtrl are "Name" and "Description": self.lc = wx.ListCtrl(self, -1, style=wx.LC_REPORT) self.lc.InsertColumn(0, 'Name') self.lc.InsertColumn(1, 'Description') And when I add a item I want them to show the Name parameter and the description: num_items = self.lc.GetItemCount() self.lc.InsertStringItem(num_items, "Randomname") self.lc.SetStringItem(num_items, 1, "Some description here") Now what I want to do is basically assign something to that item that is not shown so I can access later on the app. So I would like to add something that is not shown on the app but is on the item value like: hiddendescription = "Somerandomthing" Still didn't undestand? Well lets say I add a button to add a item with some other TextCtrls to set the parameters and the TextCtrls parameters are: "Name" "Description" "Hiddendescription" So then the user fills this textctrls out and clicks the button to create the item, and I basically want only to show the Name and Description and hide the "HiddenDescription" but to do it so I can use it later. Sorry for explaining more than 1 time on this post but I want to make sure you understand what I pretend to do.

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  • How to override built-in getattr in Python?

    - by Stephen Gross
    I know how to override an object's getattr() to handle calls to undefined object functions. However, I would like to achieve the same behavior for the builtin getattr() function. For instance, consider code like this: call_some_undefined_function() Normally, that simply produces an error: Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'call_some_undefined_function' is not defined I want to override getattr() so that I can intercept the call to "call_some_undefined_function()" and figure out what to do. Is this possible? Thanks, --Steve

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  • Python - Things one MUST avoid

    - by Anurag Uniyal
    Today I was bitten again by "Mutable default arguments" after many years. I usually don't use mutable default arguments unless needed but I think with time I forgot about that, and today in the application I added tocElements=[] in a pdf generation function's argument list and now 'Table of Content' gets longer and longer after each invocation of "generate pdf" :) My question is what other things should I add to my list of things to MUST avoid? 1 Mutable default arguments 2 import modules always same way e.g. 'from y import x' and 'import x' are totally different things actually they are treated as different modules see http://stackoverflow.com/questions/1459236/module-reimported-if-imported-from-different-path 3 Do not use range in place of lists because range() will become an iterator anyway, so things like this will fail, so wrap it by list myIndexList = [0,1,3] isListSorted = myIndexList == range(3) # will fail in 3.0 isListSorted = myIndexList == list(range(3)) # will not same thing can be mistakenly done with xrange e.g myIndexList == xrange(3). 4 Catching multiple exceptions try: raise KeyError("hmm bug") except KeyError,TypeError: print TypeError It prints "hmm bug", though it is not a bug, it looks like we are catching exceptions of type KeyError,TypeError but instead we are catching KeyError only as variable TypeError, instead use try: raise KeyError("hmm bug") except (KeyError,TypeError): print TypeError

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  • Python try/except: Showing the cause of the error after displaying my variables

    - by NealWalters
    I'm not even sure what the right words are to search for. I want to display parts of the error object in an except block (similar to the err object in VBScript, which has Err.Number and Err.Description). For example, I want to show the values of my variables, then show the exact error. Clearly, I am causing a divided-by-zero error below, but how can I print that fact? try: x = 0 y = 1 z = y / x z = z + 1 print "z=%d" % (z) except: print "Values at Exception: x=%d y=%d " % (x,y) print "The error was on line ..." print "The reason for the error was ..."

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  • Access class instance "name" dynamically in Python

    - by user328317
    In plain english: I am creating class instances dynamically in a for loop, the class then defines a few attributes for the instance. I need to later be able to look up those values in another for loop. Sample code: class A: def init(self, name, attr): self.name=name self.attr=attr names=("a1", "a2", "a3") x=10 for name in names: name=A(name, x) x += 1 ... ... ... for name in names: print name.attr How can I create an identifier for these instances so they can be accessed later on by "name"? I've figured a way to get this by associating "name" with the memory location: class A: instances=[] names=[] def init(self, name, attr): self.name=name self.attr=attr A.instances.append(self) A.names.append(name) names=("a1", "a2", "a3") x=10 for name in names: name=A(name, x) x += 1 ... ... ... for name in names: index=A.names.index(name) print "name: " + name print "att: " + str(A.instances[index].att) This has had me scouring the web for 2 days now, and I have not been able to find an answer. Maybe I don't know how to ask the question properly, or maybe it can't be done (as many other posts seemed to be suggesting). Now this 2nd example works, and for now I will use it. I'm just thinking there has to be an easier way than creating your own makeshift dictionary of index numbers and I'm hoping I didn't waste 2 days looking for an answer that doesn't exist. Anyone have anything? Thanks in advance, Andy Update: A coworker just showed me what he thinks is the simplest way and that is to make an actual dictionary of class instances using the instance "name" as the key.

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  • Creating a simple command line interface (CLI) using a python server (TCP sock) and few scripts

    - by VN44CA
    I have a Linux box and I want to be able to telnet into it (port 77557) and run few required commands without having to access to the whole Linux box. So, I have a server listening on that port, and echos the entered command on the screen. (for now) Telnet 192.168.1.100 77557 Trying 192.168.1.100... Connected to 192.168.1.100. Escape character is '^]'. hello<br /> You typed: "hello"<br /> NOW: I want to create lot of commands that each take some args and have error codes. Anyone has done this before? It would be great if I can have the server upon initialization go through each directory and execute the init.py file and in turn, the init.py file of each command call into a main template lib API (e.g. RegisterMe()) and register themselves with the server as function call backs. At least this is how I would do it in C/C++. But I want the best Pythonic way of doing this. /cmd/ /cmd/myreboot/ /cmd/myreboot/ini.py (note underscore don't show for some reason) /cmd/mylist/ /cmd/mylist/init.py ... etc IN: /cmd/myreboot/_ini_.py: from myMainCommand import RegisterMe RegisterMe(name="reboot",args=Arglist, usage="Use this to reboot the box", desc="blabla") So, repeating this creates a list of commands and when you enter the command in the telnet session, then the server goes through the list, matches the command and passed the args to that command and the command does the job and print the success or failure to stdout. Thx

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