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• Operations on Python hashes

  - by cdecker

  I've got a rather strange problem. For a Distributed Hash Table I need to be able to do some simple math operations on MD5 hashes. These include a sum (numeric sum represented by the hash) and a modulo operation. Now I'm wondering what the best way to implement these operations is. I'm using hashlib to calculate the hashes, but since the hashes I get are then string, how do I calculate with them?

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• Python: Can subclasses overload inherited methods?

  - by Rosarch

  I'm making a shopping cart app in Google App Engine. I have many classes that derive from a base handler: class BaseHandler(webapp.RequestHandler): def get(self, CSIN=None): self.body(CSIN) Does this mean that the body() method of every descendant class needs to have the same argument? This is cumbersome. Only one descendant actually uses that argument. And what about when I add new args? Do I need to go through and change every class? class Detail(BaseHandler): def body(self, CSIN): class MainPage(BaseHandler): def body(self, CSIN=None): #@UnusedVariable class Cart(BaseHandler): def body(self, CSIN): #@UnusedVariable

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• How to log python exception ?

  - by Maxim Veksler

  Hi, Coming from java, being familiar with logback I used to do try { ... catch (Exception e) { log("Error at X", e); } I would like the same functionality of being able to log the exception and the stacktrace into a file. How would you recommend me implementing this? Currently using boto logging infrastructre, boto.log.info(...) I've looked at some options and found out I can access the actual exception details using this code: import sys try: 1/0 except: exc_type, exc_value, exc_traceback = sys.exc_info() traceback.print_exception(exc_type, exc_value, exc_traceback) I would like to somehow get the string print_exception() throws to stdout so that I can log it. Thank you, Maxim.

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• Formatting floats in Python without superfluous zeros

  - by TarGz

  How to format a float so it does not containt the remaing zeros? In other words, I want the resulting string to be as short as possible..? Like: 3 -> "3" 3. -> "3" 3.1 -> "3.1" 3.14 -> "3.14" 3.140 -> "3.14"

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• Remove certain filetypes in Python

  - by Gareth

  Hello. I am running a script that walks a directory structure and generates new files in each folder in the directory. I want to delete some of the files right after creation. This is my idea, but it is quite wrong I imagine: directory = os.path.dirname(obj) m = MeshExporterApplication(directory) os.remove(os.path.join(directory,"*.mesh.xml")) How to you put wildcards in a path? I guess not like /home/me/*.txt, but that is what I am trying. Thanks, Gareth

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• Can someone here explain constructors and destructors in python - simple explanation required - new

  - by rgolwalkar

  i will try to see if it makes sense :- class Person: '''Represnts a person ''' population = 0 def __init__(self,name): //some statements and population += 1 def __del__(self): //some statements and population -= 1 def sayHi(self): '''grettings from person''' print 'Hi My name is %s' % self.name def howMany(self): '''Prints the current population''' if Person.population == 1: print 'i am the only one here' else: print 'There are still %d guyz left ' % Person.population rohan = Person('Rohan') rohan.sayHi() rohan.howMany() sanju = Person('Sanjivi') sanju.howMany() del rohan # am i doing this correctly --- ? i need to get an explanation for this del - destructor O/P:- Initializing person data ****************************************** Initializing Rohan ****************************************** Population now is: 1 Hi My name is Rohan i am the only one here Initializing person data ****************************************** Initializing Sanjivi ****************************************** Population now is: 2 In case Person dies: ****************************************** Sanjivi Bye Bye world there are still 1 people left i am the only one here In case Person dies: ****************************************** Rohan Bye Bye world i am the last person on earth Population now is: 0 If required i can paste the whole lesson as well --- learning from :- http://www.ibiblio.org/swaroopch/byteofpython/read/

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• Python: Decent config file format

  - by miracle2k

  I'd like to use a configuration file format which supports key value pairs and nestable, repeatable structures, and which is as light on syntax as possible. I'm imagining something along the lines of: cachedir = /var/cache mail_to = [email protected] job { name = my-media frequency = 1 day source { from = /home/michael/Images source { } source { } } job { } I'd be happy with something using significant-whitespace as well. JSON requires too many explicit syntax rules (quoting, commas, etc.). YAML is actually pretty good, but would require the jobs to be defined as a YAML list, which I find slightly awkward to use.

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• Django/Python best practice template_dict

  - by fredrik

  Hi, After just been coding for about 6-9 months. I probably changed my coding style a number of times after reading some code or read best practices. But one thing I haven't yet come a cross is a good why to populate the template_dict. As of now I pass the template_dict across a number of methods (that changes/modifies it) and returns is. The result is that every methods takes template_dict as first argument and the returns it and this in my eyes doesn't seems to be the best solution. An idea is to have a method that handles all the changes. But I'm curios if there's a best practice for this? Or is it "do what you feel like"-type of thing? The 2 things I think is pretty ugly is to send as an argument and return it in all methods. And the just the var name is written xxx number of times in the code :) ..fredrik

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• Download whole directories in Python SimpleHTTPServer

  - by awegawef

  I really like how I can easily share files on a network using the SimpleHTTPServer, but I wish there was an option like "download entire directory". Is there an easy (one liner) way to implement this? Thanks

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• Sorting objects in Python

  - by Curious2learn

  I want to sort objects using by one of their attributes. As of now, I am doing it in the following way USpeople.sort(key=lambda person: person.utility[chosenCar],reverse=True) This works fine, but I have read that using operator.attrgetter() might be a faster way to achieve this sort. First, is this correct? Assuming that it is correct, how do I use operator.attrgetter() to achieve this sort? I tried, keyFunc=operator.attrgetter('utility[chosenCar]') USpeople.sort(key=keyFunc,reverse=True) However, I get an error saying that there is no attribute 'utility[chosenCar]'. The problem is that the attribute by which I want to sort is in a dictionary. For example, the utility attribute is in the following form: utility={chosenCar:25000,anotherCar:24000,yetAnotherCar:24500} I want to sort by the utility of the chosenCar using operator.attrgetter(). How could I do this? Thanks in advance.

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• Get last n lines of a file with Python, similar to tail

  - by Armin Ronacher

  I'm writing a log file viewer for a web application and for that I want to paginate through the lines of the log file. The items in the file are line based with the newest item on the bottom. So I need a tail() method that can read n lines from the bottom and supports an offset. What I came up with looks like this: def tail(f, n, offset=0): """Reads a n lines from f with an offset of offset lines.""" avg_line_length = 74 to_read = n + offset while 1: try: f.seek(-(avg_line_length * to_read), 2) except IOError: # woops. apparently file is smaller than what we want # to step back, go to the beginning instead f.seek(0) pos = f.tell() lines = f.read().splitlines() if len(lines) >= to_read or pos == 0: return lines[-to_read:offset and -offset or None] avg_line_length *= 1.3 Is this a reasonable approach? What is the recommended way to tail log files with offsets?

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• Joining the previous and next sentence using python

  - by JudoWill

  I'm trying to join a set of sentences contained in a list. I have a function which determines whether a sentence in worth saving. However, in order to keep the context of the sentence I need to also keep the sentence before and after it. In the edge cases, where its either the first or last sentence then, I'll just keep the sentence and its only neighbor. An example is best: ex_paragraph = ['The quick brown fox jumps over the fence.', 'Where there is another red fox.', 'They run off together.', 'They live hapily ever after.'] t1 = lambda x: x.startswith('Where') t2 = lambda x: x'startswith('The ') The result for t1 should be: ['The quick brown fox jumps over the fence. Where there is another red fox. They run off together.'] The result for t2 should be: ['The quick brown fox jumps over the fence. Where there is another red fox.'] My solution is: def YieldContext(sent_list, cont_fun): def JoinSent(sent_list, ind): if ind == 0: return sent_list[ind]+sent_list[ind+1] elif ind == len(sent_list)-1: return sent_list[ind-1]+sent_list[ind] else: return ' '.join(sent_list[ind-1:ind+1]) for sent, sentnum in izip(sent_list, count(0)): if cont_fun(sent): yield JoinSent(sent_list, sent_num) Does anyone know a "cleaner" or more pythonic way to do something like this. The if-elif-else seems a little forced. Thanks, Will PS. I'm obviously doing this with a more complicated "context-function" but this is just for a simple example.

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• Python Mechanize select a form with no name

  - by mvid

  I am attempting to have mechanize select a form from a page, but the form in question has no "name" attribute in the html. What should I do? when I try to use br.select_form(name = "") i get errors that no form is declared with that name, and the function requires a name input. There is only one form on the page, is there some other way I can select that form?

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• Python: OSX Library for fast full screen jpg/png display

  - by Parand

  Frustrated by lack of a simple ACDSee equivalent for OS X, I'm looking to hack one up for myself. I'm looking for a gui library that accommodates: Full screen image display High quality image fit-to-screen (for display) Low memory usage Fast display Reasonable learning curve (the simpler the better) Looks like there are several choices, so which is the best? Here are some I've run across: PyOpenGL PyGame PyQT wxpython I don't have any particular experience with any of these, nor any strong desire to become an expert - I'm looking for the simplest solution. What do you recommend? [Update] For those not familiar with ACDSee, here's what it does that I care about: Simple list/thubmnail display of images in a directory Sort by name/size/type Ability to view images full screen Single-key delete while viewing full screen Move to next/previous image while viewing full screen Ability to select a group of images for: move to / copy to directory delete resize ACDSee has a bunch of niceties as well, such as remembering directories you've moved images to in the past, remembering your resize settings, displaying the total size of the images you've selected, etc. I've tried most of the options I could find (including Xee) and none of them quite get there. Please keep in mind that this is a programming/library question, not a criticism of any of the existing tools.

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• How to define and use Python generators appropriately

  - by Morlock

  I want to define a generator from a list that will output the elements one at a time, then use this generator object in an appropriate manner. a = ["Hello", "world", "!"] b = (x for x in a) c = next(b, None) while c != None: print c, c = next(b, None) Is there anything wrong or improvable with the while approach here? Is there a way to avoid having to assign 'c' before the loop? Thanks!

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• Converting python objects for rpy2

  - by bgbg

  The following code is supposed to created a heatmap in rpy2 import numpy as np from rpy2.robjects import r data = np.random.random((10,10)) r.heatmap(data) However, it results in the following error Traceback (most recent call last): File "z.py", line 8, in <module> labRow=rowNames, labCol=colNames) File "C:\Python25\lib\site-packages\rpy2\robjects\__init__.py", line 418, in __call__ new_args = [conversion.py2ri(a) for a in args] File "C:\Python25\lib\site-packages\rpy2\robjects\__init__.py", line 93, in default_py2ri raise(ValueError("Nothing can be done for the type %s at the moment." %(type(o)))) ValueError: Nothing can be done for the type <type 'numpy.ndarray'> at the moment. From the documentation I learn that r.heatmap expects "a numeric matrix". How do I convert np.array to the required data type?

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• Cleaning an XML file in Python before parsing

  - by Sam

  I'm using minidom to parse an xml file and it threw an error indicating that the data is not well formed. I figured out that some of the pages have characters like ไอเฟล &, causing the parser to hiccup. Is there an easy way to clean the file before I start parsing it? Right now I'm using a regular expressing to throw away anything that isn't an alpha numeric character and the </> characters, but it isn't quite working.

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• Python key word arguments

  - by pythonic metaphor

  I have several layers of function calls, passing around a common dictionary of key word arguments: def func1(**qwargs): func2(**qwargs) func3(**qwargs) I would like to supply some default arguments in some of the subsequent function calls, something like this: def func1(**qwargs): func2(arg = qwargs.get("arg", default), **qwargs) func3(**qwargs) The problem with this approach is that if arg is inside qwargs, a TypeError is raised with "got multiple values for keyword argument". I don't want to set qwargs["arg"] to default, because then func3 gets this argument without warrant. I could make a copy.copy of the qwargs and set "arg" in the copy, but qwargs could have large data structures in it and I don't want to copy them (maybe copy.copy wouldn't, only copy.deepcopy?). What's the pythonic thing to do here?

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• python dict function on enumerate object

  - by Lundus

  Hi, If I have an enumerate object x, why does doing the following: dict(x) clear all the items in the enumerate sequence?

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• Python class decorator and maximum recursion depth exceeded

  - by Michal Lula

  I try define class decorator. I have problem with __init__ method in decorated class. If __init__ method invokes super the RuntimeError maximum recursion depth exceeded is raised. Code example: def decorate(cls): class NewClass(cls): pass return NewClass @decorate class Foo(object): def __init__(self, *args, **kwargs): super(Foo, self).__init__(*args, **kwargs) What I doing wrong? Thanks, Michal

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• Copy whole SQL Server database into JSON from Python

  - by Oli

  I facing an atypical conversion problem. About a decade ago I coded up a large site in ASP. Over the years this turned into ASP.NET but kept the same database. I've just re-done the site in Django and I've copied all the core data but before I cancel my account with the host, I need to make sure I've got a long-term backup of the data so if it turns out I'm missing something, I can copy it from a local copy. To complicate matters, I no longer have Windows. I moved to Ubuntu on all my machines some time back. I could ask the host to send me a backup but having no access to a machine with MSSQL, I wouldn't be able to use that if I needed to. So I'm looking for something that does: db = {} for table in database: db[table.name] = [row for row in table] And then I could serialize db off somewhere for later consumption... But how do I do the table iteration? Is there an easier way to do all of this? Can MSSQL do a cross-platform SQLDump (inc data)? For previous MSSQL I've used pymssql but I don't know how to iterate the tables and copy rows (ideally with column headers so I can tell what the data is). I'm not looking for much code but I need a poke in the right direction.

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• In python: how to apply itertools.product to elements of a list of lists

  - by Guilherme Rocha

  I have a list of arrays and I would like to get the cartesian product of the elements in the arrays. I will use an example to make this more concrete... itertools.product seems to do the trick but I am stuck in a little detail. arrays = [(-1,+1), (-2,+2), (-3,+3)]; If I do cp = list(itertools.product(arrays)); I get cp = cp0 = [((-1, 1),), ((-2, 2),), ((-3, 3),)] But what I want to get is cp1 = [(-1,-2,-3), (-1,-2,+3), (-1,+2,-3), (-1,+2,+3), ..., (+1,+2,-3), (+1,+2,+3)]. I have tried a few different things: cp = list(itertools.product(itertools.islice(arrays, len(arrays)))); cp = list(itertools.product(iter(arrays, len(arrays)))); They all gave me cp0 instead of cp1. Any ideas? Thanks in advance.

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• A Python Wrapper for Shutterfly. Uploading an Image

  - by iJames

  I'm working on a Django app in which I want to order prints through Shutterfly's Open API: http://www.shutterfly.com/documentation/start.sfly So far I've been able to build the appropriate POSTs and GETs using the modules and suggested code snippets including httplib, httplib2, urllib, urllib2, mimetype, etc. But I'm stuck on the image uploading when placing an order (the ordering process is not the same process as uploading images to albums which I haven't tried.) From what I can tell, I'm supposed to basically create the multipart form data by concatenating the HTTP request body together with the binary data of the image. I take the strings: --myuniqueboundary1273149960.175.1 Content-Disposition: form-data; name="AuthenticationID" auniqueauthenticationid --myuniqueboundary1273149960.175.1 Content-Disposition: file; name="Image.Data"; filename="1_41_orig.jpg" Content-Type: image/jpeg and I put this data into it and end with the final boundary: ...\xb5|\xf88\x1dj\t@\xd9\'\x1f\xc6j\x88{\x8a\xc0\x18\x8eGaJG\x03\xe9J-\xd8\x96[\x91T\xc3\x0eTu\xf4\xaa\xa5Ty\x80\x01\x8c\x9f\xe9Z\xad\x8cg\xba# g\x18\xe2\xaa:\x829\x02\xb4["\x17Q\xe7\x801\xea?\xad7j\xfd\xa2\xdf\x81\xd2\x84D\xb6)\xa8\xcb\xc8O\\\x9a\xaf(\x1cqM\x98\x8d*\xb8\'h\xc8+\x8e:u\xaa\xf3*\x9b\x95\x05F8\xedN%\xcb\xe1B2\xa9~Tw\xedF\xc4\xfe\xe8\xfc\xa9\x983\xff\xd9... That ends up making it look like this (when I use print to debug): ... --myuniqueboundary1273149960.175.1 Content-Disposition: file; name="Image.Data"; filename="1_41_orig.jpg" Content-Type: image/jpeg ????q?ExifMM* ? ??(1?2?<??i?b?NIKON CORPORATIONNIKON D40HHQuickTime 7.62009:02:17 13:05:25Mac OS X 10.5.6%??????"?'??0220?????? ???? ? ?|_???,b???50??5 ... --myuniqueboundary1273149960.175.1-- My code for grabbing the binary data is pretty much this: filedata = open('myjpegfile.jpeg','rb').read() Which I then add to the rest of the body. I've see something like this code everywhere. I'm then using this to post the full request (with the headers too): response = urllib2.urlopen(request).read() This seems to me to be the standard way that form POSTS with files happens. Am I missing something here? At some point I might be able to make this into a library worth posting up on github, but this problem has stopped me cold in my tracks. Thanks for any insight!

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• recursively implementing 'minimum number of coins' in python

  - by user5198

  This problem is same as asked in here. Given a list of coins, their values (c1, c2, c3, ... cj, ...), and the total sum i. Find the minimum number of coins the sum of which is i (we can use as many coins of one type as we want), or report that it's not possible to select coins in such a way that they sum up to S. I"m just introduced to dynamic programming yesterday and I tried to make a code for it. # Optimal substructure: C[i] = 1 + min_j(C[i-cj]) cdict = {} def C(i, coins): if i <= 0: return 0 if i in cdict: return cdict[i] else: answer = 1 + min([C(i - cj, coins) for cj in coins]) cdict[i] = answer return answer Here, C[i] is the optimal solution for amount of money 'i'. And available coins are {c1, c2, ... , cj, ...} for the program, I've increased the recursion limit to avoid maximum recursion depth exceeded error. But, this program gives the right answer only someones and when a solution is not possible, it doesn't indicate that. What is wrong with my code and how to correct it?

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• Fast iterating over first n items of an iterable in python

  - by martinthenext

  Hello! I'm looking for a pythonic way of iterating over first n items of a list, and it's quite important to do this as fast as possible. This is how I do it now: count = 0 for item in iterable: do_somethin(item) count += 1 if count >= n: break Doesn't seem neat to me. Another way of doing this is: for item in itertools.islice(iterable, n): do_something(item) This looks good, the question is it fast enough to use with some generator(s)? For example: pair_generator = lambda iterable: itertools.izip(*[iter(iterable)]*2) for item in itertools.islice(pair_generator(iterable), n): so_something(item) Will it run fast enough as compared to the first method? Is there some easier way to do it?

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