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• Python begineer confused by a piece of code

  - by Protean

  I understand the gist of the code, that it forms permutations; however, I was wondering if someone could explain exactly what is going on in the return statement. def perm(l): sz = len(l) print (l) if sz <= 1: print ('sz <= 1') return [l] return [p[:i]+[l[0]]+p[i:] for i in range(sz) for p in perm(l[1:])]

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• Python __import__ parameter confusion

  - by CMC

  I'm trying to import a module, while passing some global variables, but it does not seem to work: File test_1: test_2 = __import__("test_2", {"testvar": 1}) File test_2: print testvar This seems like it should work, and print a 1, but I get the following error when I run test_1: Traceback (most recent call last): File ".../test_1.py", line 1, in <module> print testvar NameError: name 'testvar' is not defined What am I doing wrong?

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• How to read a file with variable multi-row data in Python

  - by dr.bunsen

  I have a file that is about 100Mb that looks like this: #meta data 1 skadjflaskdjfasljdfalskdjfl sdkfjhasdlkgjhsdlkjghlaskdj asdhfk #meta data 2 jflaksdjflaksjdflkjasdlfjas ldaksjflkdsajlkdfj #meta data 3 alsdkjflasdjkfglalaskdjf This file contains one row of meta data that corresponds to several, variable length data containing only alpha-numeric characters. What is the best way to read this data into a simple list like this: data = [[#meta data 1, skadjflaskdjfasljdfalskdjflsdkfjhasdlkgjhsdlkjghlaskdjasdhfk], [#meta data 2, jflaksdjflaksjdflkjasdlfjasldaksjflkdsajlkdfj], [#meta data 3, alsdkjflasdjkfglalaskdjf]] My initial idea was to use the read() method to read the whole file into memory and then use regular expressions to parse the data into the desired format. Is there a better more pythonic way? All metadata lines start with an octothorpe and all data lines are all alpha-numeric. Thanks!

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• Python: For loop problem

  - by Yasmin

  I have a simple for loop problem, when i run the code below it prints out series of 'blue green' sequences then a series of 'green' sequences. I want the output to be; if row[4] is equal to 1 to print blue else print green. for row in rows: for i in `row[4]`: if i ==`1`: print 'blue ' else: print 'green ' Any help would be grateful thanks Yas

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• Concise way to getattr() and use it if not None in Python

  - by MTsoul

  I am finding myself doing the following a bit too often: attr = getattr(obj, 'attr', None) if attr is not None: attr() # Do something, either attr(), or func(attr), or whatever else: # Do something else Is there a more pythonic way of writing that? Is this better? (At least not in performance, IMO.) try: obj.attr() # or whatever except AttributeError: # Do something else

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• String concatenation produces incorrect output in Python?

  - by Brian

  I have this code: filenames=["file1","FILE2","file3","fiLe4"] def alignfilenames(): #build a string that can be used to add labels to the R variables. #format goal: suffixes=c(".fileA",".fileB") filestring='suffixes=c(".' for filename in filenames: filestring=filestring+str(filename)+'",".' print filestring[:-3] #now delete the extra characters filestring=filestring[-1:-4] filestring=filestring+')' print "New String" print str(filestring) alignfilenames() I'm trying to get the string variable to look like this format: suffixes=c(".fileA",".fileB".....) but adding on the final parenthesis is not working. When I run this code as is, I get: suffixes=c(".file1",".FILE2",".file3",".fiLe4" New String ) Any idea what's going on or how to fix it?

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• A problem with assertRaises function in Python

  - by anton.k.

  Hello,guys! I am trying to run the following test self.assertRaises(Exception,lambda: unit_test.testBasic()) where test.testBasic() is class IsPrimeTest(unittest.TestCase): def assertRaises(self,exception,callable,*args,**kwargs): print('dfdf') temp = callable super().assertRaises(exception,temp,*args,**kwargs) def testBasic_helper(self): self.failIf(is_prime(2)) self.assertTrue(is_prime(1)) where prime is a function,and but in self.assertRaises(Exception,lambda: unit_test.testBasic()) the lambda function doesnt throws an exception after the test def testBasic_helper(self): self.failIf(is_prime(2)) self.assertTrue(is_prime(1)) fails Can somebody offers a solution to the problem?

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• Access static class variable of parent class in Python

  - by fuenfundachtzig

  I have someting like this class A: __a = 0 def __init__(self): A.__a = A.__a + 1 def a(self): return A.__a class B(A): def __init__(self): # how can I access / modify A.__a here? A.__a = A.__a + 1 # does not work def a(self): return A.__a Can I access the __astatic variable in B? It's possible writing a instead of __a, is this the only way? (I guess the answer might be rather short: yes :)

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• Recognizing file - Python

  - by Francisco Aleixo

  Ok, so the title may trick you a bit, and I'm sorry for that but didn't find a better title. This question might be a bit hard to understand so I'll try my best. I have no idea how this works or if it is even possible but what I want to do is for example create a file type (lets imagine .test (in which a random file name would be random.test)). Now before I continue, its obviously easy to do this using for example: filename = "random.test" file = open(filename, 'w') file.write("some text here") But now what I would like to know is if it is possible to write the file .test so if I set it to open with a wxPython program, it recognizes it and for example opens up a Message Dialog automatically. I'm sorry if I'm being vague and in case you don't understand, let me know so I can try my best to explain you.

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• Best practice for Python Assert

  - by meade

  Is there a performance or code maintenance issue with using assert as part of the standard code instead of using it just for debugging purposes? Is assert x >= 0, 'x is less then zero' and better or worse then if x < 0: raise Exception, 'x is less then zero' Also, is there anyway to set a business rule like if x < 0 raise error that is always checked with out the try, except, finally so, if at anytime throughout the code x is < 0 an error is raised, like if you set assert x < 0 at the start of a function, anywhere within the function where x becomes less then 0 an exception is raised?

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• How can I dispatch Firefox with Python?

  - by Shady

  How can I do this with Firefox? ie = win32com.client.Dispatch('InternetExplorer.Application') ie.visible = 1 ie.navigate('http://google.com') Is there a way to do it?

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• finding max in python as per some custom criterion

  - by MK

  Hi, I can do max(s) to find the max of a sequence. But suppose I want to compute max according to my own function , something like so - currmax = 0 def mymax(s) : for i in s : #assume arity() attribute is present currmax = i.arity() if i.arity() > currmax else currmax Is there a clean pythonic way of doing this? Thanks!

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• Python: Converting a tuple to a string with 'err'

  - by skylarking

  Given this : import os import subprocess def check_server(): cl = subprocess.Popen(["nmap","10.7.1.71"], stdout=subprocess.PIPE) result = cl.communicate() print result check_server() check_server() returns this tuple: ('\nStarting Nmap 4.53 ( http://insecure.org ) at 2010-04-07 07:26 EDT\nInteresting ports on 10.7.1.71:\nNot shown: 1711 closed ports\nPORT STATE SERVICE\n21/tcp open ftp\n22/tcp open ssh\n80/tcp open http\n\nNmap done: 1 IP address (1 host up) scanned in 0.293 seconds\n', None) Changing the second line in the method to result, err = cl.communicate() results in check_server() returning : Starting Nmap 4.53 ( http://insecure.org ) at 2010-04-07 07:27 EDT Interesting ports on 10.7.1.71: Not shown: 1711 closed ports PORT STATE SERVICE 21/tcp open ftp 22/tcp open ssh 80/tcp open http Nmap done: 1 IP address (1 host up) scanned in 0.319 seconds Looks to be the case that the tuple is converted to a string, and the \n's are being stripped.... but how? What is 'err' and what exactly is it doing?

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• Python: how to execute generated code ?

  - by Natim

  Hello guys I have this code, and I would like to use the app parameter to generate the code instead of duplicating it. if app == 'map': try: from modulo.map.views import map return map(request, *args, **kwargs) except ImportError: pass elif app == 'schedule': try: from modulo.schedule.views import schedule_day return schedule_day(request, *args, **kwargs) except ImportError: pass elif app == 'sponsors': try: from modulo.sponsors.views import sponsors return sponsors(request, *args, **kwargs) except ImportError: pass elif app == 'streaming': try: from modulo.streaming.views import streaming return streaming(request, *args, **kwargs) except ImportError: pass Do you have any idea ? Thanks

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• Python - Subprocess Popen and Thread error

  - by n0idea

  In both functions record and ftp, i have subprocess.Popen if __name__ == '__main__': try: t1 = threading.Thread(target = record) t1.daemon = True t1.start() t2 = threading.Thread(target = ftp) t2.daemon = True t2.start() except (KeyboardInterrupt, SystemExit): sys.exit() The error I'm receiving is: Exception in thread Thread-1 (most likely raised during interpreter shutdown): Traceback (most recent call last): File "/usr/lib/python2.7/threading.py", line 551, in __bootstrap_inner File "/usr/lib/python2.7/threading.py", line 504, in run File "./in.py", line 20, in recordaudio File "/usr/lib/python2.7/subprocess.py", line 493, in call File "/usr/lib/python2.7/subprocess.py", line 679, in __init__ File "/usr/lib/python2.7/subprocess.py", line 1237, in _execute_child <type 'exceptions.AttributeError'>: 'NoneType' object has no attribute 'close' What might the issue be ?

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• Invalid syntax in this simple Python application.

  - by Sergio Boombastic

  Getting an invalid syntax when creating the template_value variable: class MainPage(webapp.RequestHandler): def get(self): blogPosts_query = BlogPost.all().order('-postDate') blogPosts = blogPosts_query.fetch(10) if users.get_current_user(): url = users.create_logout_url(self.request.uri) url_linktext = 'Logout' else: url = url = users.create_login_url(self.request.uri) url_linktext = 'Login' template_value = ( 'blogPosts': blogPosts, 'url': url, 'url_linktext': url_linktext, ) path = os.path.join(os.path.dirname(__file__), 'index.html') self.response.out.write(template.render(path, template_values)) The error fires specifically on the 'blogPosts': blogPosts line. What am I doing wrong? Thanks!

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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 iterators and thread-safety

  - by Igor

  I have a class which is being operated on by two functions. One function creates a list of widgets and writes it into the class: def updateWidgets(self): widgets = self.generateWidgetList() self.widgets = widgets the other function deals with the widgets in some way: def workOnWidgets(self): for widget in self.widgets: self.workOnWidget(widget) each of these functions runs in it's own thread. the question is, what happens if the updateWidgets() thread executes while the workOnWidgets() thread is running? I am assuming that the iterator created as part of the for...in loop will keep some kind of reference to the old self.widgets object? So I will finish iterating over the old list... but I'd love to know for sure.

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• python file manipulation

  - by lakshmipathi

  I have a directory /tmp/dir with two types of file names /tmp/dir/abc-something-server.log /tmp/dir/xyz-something-server.log .. .. and /tmp/dir/something-client.log I need append a few lines (these lines are constant) to files end with "client.log" line 1 line 2 line 3 line 4 append these four lines to files end with "client.log" and For files end with "server.log" I needed to append after a keyword say "After-this". "server.log " file has multiple entries of "After-this" I need to find the first entry of "After-this" and append above said four lines keep the remaining file as it is. Any help will be great appreciated :) Thanks in advance.

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• Python Script to check website for a tag

  - by LinuxGnut

  Hello all. I'm trying to figure out how to go about writing a website monitoring script (cron job in the end) to open up a given URL, check to see if a tag exists, and if the tag does not exist, or doesn't contain the expected data, then to write some to a log file, or to send an e-mail. The tag would be something like or something relatively similar. Anyone have any ideas?

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• What are the steps taken with pip install in python

  - by Lawrence Chernin

  I am trying to install a package via pip, but there were missing files from the zip file. So I copy the files and then compile with gcc. But now I cannot continue with the installation by calling pip install because it sees a pre-existing directory and will not proceed. This is with pip version 1.5.6, but I thought that with earlier versions of pip that it was less fussy about this. What are the remaining steps to complete the package installation?

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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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• Split a string in python taking care of quotes

  - by santu

  I want to extract key value pairs of some form elements in a html page for example name="frmLogin" method="POST" onSubmit="javascript:return validateAndSubmit();" action="TG_cim_logon.asp?SID=^YcMunDFDQUoWV32WPUMqPxeSxD4L_slp_rhc_rNvW7Fagp7FgH3l0uJR/3_slp_rhc_dYyJ_slp_rhc_vsPW0kJl&RegType=Lite_Home" is there any method using which I can safely get the key and value pairs. I tried using splitting by spaces and then using '=' characters but string inside quotes can also have '='. is there any different kind of split method which can also take care of quotes?

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• Python: import the containing package

  - by guy

  In a module residing inside a package, i have the need to use a function defined within the __init__.py of that package. how can i import the package within the module that resides within the package, so i can use that function? Importing __init__ inside the module will not import the package, but instead a module named __init__, leading to two copies of things with different names... Is there a pythonic way to do this?

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• sorting in python

  - by tipu

  I have a hashmap like so: results[tweet_id] = {"score" : float(dot(query,doc) / (norm(query) * norm(doc))), "tweet" : tweet} What I'd like to do is to sort results by the innser "score" key. I don't know how possible this is, I saw many sorting tutorials but they were for simple (not nested) data structures.

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