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  • Accessing items from a dictionary using pickle efficiently in Python

    - by user248237
    I have a large dictionary mapping keys (which are strings) to objects. I pickled this large dictionary and at certain times I want to pull out only a handful of entries from it. The dictionary has usually thousands of entries total. When I load the dictionary using pickle, as follows: from cPickle import * # my dictionary from pickle, containing thousands of entries mydict = open(load('mypickle.pickle')) # accessing only handful of entries here for entry in relevant_entries: # find relevant entry value = mydict[entry] I notice that it can take up to 3-4 seconds to load the entire pickle, which I don't need, since I access only a tiny subset of the dictionary entries later on (shown above.) How can I make it so pickle only loads those entries that I have from the dictionary, to make this faster? Thanks.

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  • How to lazy load a data structure (python)

    - by Anton Geraschenko
    I have some way of building a data structure (out of some file contents, say): def loadfile(FILE): return # some data structure created from the contents of FILE So I can do things like puppies = loadfile("puppies.csv") # wait for loadfile to work kitties = loadfile("kitties.csv") # wait some more print len(puppies) print puppies[32] In the above example, I wasted a bunch of time actually reading kitties.csv and creating a data structure that I never used. I'd like to avoid that waste without constantly checking if not kitties whenever I want to do something. I'd like to be able to do puppies = lazyload("puppies.csv") # instant kitties = lazyload("kitties.csv") # instant print len(puppies) # wait for loadfile print puppies[32] So if I don't ever try to do anything with kitties, loadfile("kitties.csv") never gets called. Is there some standard way to do this? After playing around with it for a bit, I produced the following solution, which appears to work correctly and is quite brief. Are there some alternatives? Are there drawbacks to using this approach that I should keep in mind? class lazyload: def __init__(self,FILE): self.FILE = FILE self.F = None def __getattr__(self,name): if not self.F: print "loading %s" % self.FILE self.F = loadfile(self.FILE) return object.__getattribute__(self.F, name) What might be even better is if something like this worked: class lazyload: def __init__(self,FILE): self.FILE = FILE def __getattr__(self,name): self = loadfile(self.FILE) # this never gets called again # since self is no longer a # lazyload instance return object.__getattribute__(self, name) But this doesn't work because self is local. It actually ends up calling loadfile every time you do anything.

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  • python tarfile adding files without directory hiearchy

    - by theactiveactor
    When I invoke add() on a tarfile object with a file path, the file is added to the tarball with directory hiearchy associated .In other words, if I unzip the tarfile the directories in the original dir hiearchy are reproduced. Is there a way to simply add a plainfile without directory info that untarring the resulting tarball produce a flat list of files?

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  • convert the key in MIME encoded form in python

    - by jaysh
    this is the code : f = urllib.urlopen('http://pool.sks-keyservers.net:11371/pks/lookup?op=get&search= 0x58e9390daf8c5bf3') #Retrieve the public key from PKS data = f.read() decoded_bytes = base64.b64decode(data) print decoded_bytes i need to convert the key in MIME encoded form which is presently comes in (ascii armored) radix 64 format.for that i have to get this radix64 format in its binary form and also need to remove its header and checksum than coversion in MIME format but i didnt find any method which can do this conversion. i used the base64.b64decode method and its give me error: Traceback (most recent call last): File "RetEnc.py", line 12, in ? decoded_bytes = base64.b64decode(data) File "/usr/lib/python2.4/base64.py", line 76, in b64decode raise TypeError(msg) TypeError: Incorrect padding what to do i'didnt getting .can anybody suggest me something related to this...... thanks!!!!

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  • Python sort 2-D list by time string

    - by Mark Kennedy
    How do I sort a multi dimensional list like this based on a time string? The sublists can be of different sizes (i.e. 4 and 5, here) I want to sort by comparing the first time string in each sublist (sublist[-4]) x = (['1513', '08:19PM', '10:21PM', 1, 4], ['1290', '09:45PM', '11:43PM', 1, 4], ['0690', '07:25AM', '09:19AM', 1, 4], ['0201', '08:50AM', '10:50AM', 1, 4], ['1166', '04:35PM', '06:36PM', 1, 4], ['0845', '05:40PM', '07:44PM', 1, 4], ['1267', '07:05PM', '09:07PM', 1, 4], ['1513', '08:19PM', '10:21PM', 1, 4], ['1290', '09:45PM', '11:43PM', 1, 4], ['8772', '0159', '12:33PM', '02:43PM', 1, 5], ['0888', '0570', '09:42PM', '12:20AM', 1, 5], ['2086', '2231', '04:10PM', '06:20PM', 1, 5]) The sorted result would be sortedX = (['0690', '07:25AM', '09:19AM', 1, 4], ['0201', '08:50AM', '10:50AM', 1, 4], ['1166', '04:35PM', '06:36PM', 1, 4], ['0845', '05:40PM', '07:44PM', 1, 4], ['1267', '07:05PM', '09:07PM', 1, 4], ['1513', '08:19PM', '10:21PM', 1, 4], ['1513', '08:19PM', '10:21PM', 1, 4], ['1290', '09:45PM', '11:43PM', 1, 4], ['1290', '09:45PM', '11:43PM', 1, 4], ['8772', '0159', '12:33PM', '02:43PM', 1, 5], ['2086', '2231', '04:10PM', '06:20PM', 1, 5], ['0888', '0570', '09:42PM', '12:20AM', 1, 5]) I tried the following: sortedX = sorted(x, key=lambda k : k[-4]) #k[-4] is the first time string and it works but it doesn't respect the sublist size ordering

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  • Catch clearly defined exception from sub.submodule in python

    - by mynthon
    I have 3 files. xxx which imports xxx2 and xxx2 imports xxx3 which one raises OppsError exception. xxx3.py: class OppsError(Exception):pass def go(): raise OppsError() xxx2.py: import xxx3 xxx3.go() xxx.py: try: import xxx2 except xxx3.OppsError: print 'ops' When i run xxx.py i get error NameError: name 'xxx3' is not defined. Is importing xxx3 inside xxx only way to catch OppsError?

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  • Multiple levels of 'collection.defaultdict' in Python

    - by Morlock
    Thanks to some great folks on SO, I discovered the possibilities offered by collections.defaultdict, notably in readability and speed. I have put them to use with success. Now I would like to implement three levels of dictionaries, the two top ones being defaultdict and the lowest one being int. I don't find the appropriate way to do this. Here is my attempt: from collections import defaultdict d = defaultdict(defaultdict) a = [("key1", {"a1":22, "a2":33}), ("key2", {"a1":32, "a2":55}), ("key3", {"a1":43, "a2":44})] for i in a: d[i[0]] = i[1] Now this works, but the following, which is the desired behavior, doesn't: d["key4"]["a1"] + 1 I suspect that I should have declared somewhere that the second level defaultdict is of type int, but I didn't find where or how to do so. The reason I am using defaultdict in the first place is to avoid having to initialize the dictionary for each new key. Any more elegant suggestion? Thanks pythoneers!

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  • Automatically registering "commands" for a command line program in python

    - by seandavi
    I would like to develop a command-line program that can process and give "help" for subcommands. To be concrete, say I have a single script called "cgent" and I would like to have subcommands "abc", "def", and "xyz" execute and accept the rest of the sys.args for processing by optparse. cgent abc [options] cgent help abc .... All of this is straightforward if I hard-code the subcommand names. However, I would like to be able to continue to add subcommands by adding a class or module (?). This is similar to the idea that is used by web frameworks for adding controllers, for example. I have tried digging through pylons to see if I can recreate what is done there, but I have not unravelled the logic. Any suggestions on how to do this? Thanks, Sean

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  • Python - Removing duplicates from a string

    - by Daniel
    def remove_duplicates(strng): """ Returns a string which is the same as the argument except only the first occurrence of each letter is present. Upper and lower case letters are treated as different. Only duplicate letters are removed, other characters such as spaces or numbers are not changed. >>> remove_duplicates('apple') 'aple' >>> remove_duplicates('Mississippi') 'Misp' >>> remove_duplicates('The quick brown fox jumps over the lazy dog') 'The quick brown fx jmps v t lazy dg' >>> remove_duplicates('121 balloons 2 u') '121 balons 2 u' """ s = strng.split() return strng.replace(s[0],"") Writing a function to get rid of duplicate letters but so far have been playing around for an hour and can't get anything. Help would be appreciated, thanks.

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  • Python: why can't descriptors be instance variables?

    - by Continuation
    Say I define this descriptor: class MyDescriptor(object): def __get__(self, instance, owner): return self._value def __set__(self, instance, value): self._value = value def __delete__(self, instance): del(self._value) And I use it in this: class MyClass1(object): value = MyDescriptor() >>> m1 = MyClass1() >>> m1.value = 1 >>> m2 = MyClass1() >>> m2.value = 2 >>> m1.value 2 So value is a class attribute and is shared by all instances. Now if I define this: class MyClass2(object) value = 1 >>> y1 = MyClass2() >>> y1.value=1 >>> y2 = MyClass2() >>> y2.value=2 >>> y1.value 1 In this case value is an instance attribute and is not shared by the instances. Why is it that when value is a descriptor it can only be a class attribute, but when value is a simple integer it becomes an instance attribute?

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  • How to do elif statments more elegantly if appending to array in python

    - by user1741339
    I am trying to do a more elegant version of this code. This just basically appends a string to categorynumber depending on the number. Would appreciate any help. number = [100,150,200,500] categoryNumber = [] for i in range (0,len(number)): if (number [i] >=1000): categoryNumber.append('number > 1000') elif (number [i] >=200): categoryNumber.append('200 < number < 300') elif (number [i] >=100): categoryNumber.append('100 < number < 200') elif (number [i] >=50): categoryNumber.append('50 < number < 100') elif (number [i] < 50): categoryNumber.append('number < 50') for i in range(0,len(categoryNumber)): print i

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  • (Python) algorithm to randomly select a key based on proportionality/weight

    - by LaundroMat
    Hi - I'm a bit at a loss as to how to find a clean algorithm for doing the following: Suppose I have a dict k: >>> k = {'A': 68, 'B': 62, 'C': 47, 'D': 16, 'E': 81} I now want to randomly select one of these keys, based on the 'weight' they have in the total (i.e. sum) amount of keys. >>> sum(k.values()) >>> 274 So that there's a >>> 68.0/274.0 >>> 0.24817518248175183 24.81% percent change that A is selected. How would you write an algorithm that takes care of this? In other words, that makes sure that on 10.000 random picks, A will be selected 2.481 times?

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  • Network Communication program in python

    - by lamnep
    Hi all, Basically what I'm trying to achieve is a program which allow users to connect to a each other over a network in, essentially, a chat room. What I'm currently struggling with is writing the code so that the users can connect to each other without knowing the IP-address of the computer that the other users are using or knowing the IP-address of a server. Does anyone know of a way in which I could simply have all of the users scan the IP range of my network in order to find any active 'room' and then give the user a chance to connect to it? Also, the hope is that there will be no need for a central server to run this from, rather every user will simply be connected to all other user, essentially being the server and client at the same time.

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  • python win32api registery key change

    - by user340495
    Hi, I am trying to trigger an event every time a registry value is being modified. import win32api import win32event import win32con import _winreg key = _winreg.OpenKey(_winreg.HKEY_CURRENT_USER,'Control Panel\Desktop',0,_winreg.KEY_READ) sub_key = _winreg.CreateKey(key,'Wallpaper') evt = win32event.CreateEvent(None,0,0,None) win32api.RegNotifyChangeKeyValue(sub_key,1,win32api.REG_NOTIFY_CHANGE_ATTRIBUTES,evt,True) ret_code=win32event.WaitForSingleObject(evt,3000) if ret_code == win32con.WAIT_OBJECT_0: print "CHANGED" if ret_code == win32con.WAIT_TIMEOUT: print "TIMED" my problem is that this is never triggered , the event always time-out. (the reg key I am trying to follow is the wallpaper) [ please note I trigger the event by 1) manually changing the registry value in regedit 2) an automated script which run this : from ctypes import windll from win32con import * windll.user32.SystemParametersInfoA(SPI_SETDESKWALLPAPER, 0,"C:\wall.jpg",SPIF_UPDATEINIFILE | SPIF_SENDWININICHANGE) ] Thanks for any help in advance :) EDIT:: sorry about formatting

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  • Python unittest: Generate multiple tests programmatically?

    - by Rosarch
    I have a function to test, under_test, and a set of expected input/output pairs: [ (2, 332), (234, 99213), (9, 3), # ... ] I would like each one of these input/output pairs to be tested in its own test_* method. Is that possible? This is sort of what I want, but forcing every single input/output pair into a single test: class TestPreReqs(unittest.TestCase): def setUp(self): self.expected_pairs = [(23, 55), (4, 32)] def test_expected(self): for exp in self.expected_pairs: self.assertEqual(under_test(exp[0]), exp[1]) if __name__ == '__main__': unittest.main()

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  • python send/receive hex data via TCP socket

    - by Mike
    I have a ethenet access control device that is said to be able to communicate via TCP. How can i send a pachet by entering the HEX data, since this is what i have from their manual (a standard format for the communication packets sent and received after each command)

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  • Efficient way to build a MySQL update query in Python

    - by ensnare
    I have a class variable called attributes which lists the instance variables I want to update in a database: attributes = ['id', 'first_name', 'last_name', 'name', 'name_url', 'email', 'password', 'password_salt', 'picture_id'] Each of the class attributes are updated upon instantiation. I would like to loop through each of the attributes and build a MySQL update query in the form of: UPDATE members SET id = self._id, first_name = self._first name ... Thanks.

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  • Number of elements in Python Set

    - by Tim
    I have a list of phone numbers that have been dialed (nums_dialed). I also have a set of phone numbers which are the number in a client's office (client_nums) How do I efficiently figure out how many times I've called a particular client (total) For example: >>>nums_dialed=[1,2,2,3,3] >>>client_nums=set([2,3]) >>>??? total=4 Problem is that I have a large-ish dataset: len(client_nums) ~ 10^5; and len(nums_dialed) ~10^3.

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  • python matrices - list index out of range

    - by user1888493
    I am writing a function, that takes a matrix as input, such as the one below. Then the it returns the matrix' inverse, where all the 1s are changed to 0s and all the 0s changed to 1s, while keeping the diagonal from top left to bottom right 0s. An example input: g1 = [[0, 1, 1, 0], [1, 0, 0, 1], [1, 0, 0, 1], [0, 1, 1, 0]] the function should output this: g1 = [[0, 0, 0, 1], [0, 0, 1, 0], [0, 1, 0, 0], [1, 0, 0, 0]] When I run the program, it raises a list index out of range error. I'm sure this happens, because the loops I have set up are trying to access values that do not exist. But how do I allow an input of unknown row and column size? I only know how to do this with a single list, but a list of lists? Following you see the transforming function, but not the test function that calls it: def inverse_graph(graph): # take in graph # change all zeros to ones and ones to zeros r, c = 0, 0 # row, column equal zero while (graph[r][c] == 0 or graph[r][c] == 1): # while the current row has a value. while (graph[r][c] == 0 or graph[r][c] == 1): # while the current column has a value if (graph[r][c] == 0): graph[r][c] = 1 elif (graph[r][c] == 1): graph[r][c] = 0 c+=1 c=0 r+=1 c=0 r=0 # sets diagonal to zeros while (g1[r][c] == 0 or g1[r][c] == 1): g1[r][c]=0 c+=1 r+=1 return graph

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