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• How to reproduce System.Security.Cryptography.SHA1Managed result in Python

  - by joetyson

  Here's the deal: I'm moving a .NET website to Python. I have a database with passwords hashed using the System.Security.Cryptography.SHA1Managed utility. I'm creating the hash in .NET with the following code: string hashedPassword = Cryptographer.CreateHash("MYHasher", userInfo.Password); The MYHasher block looks like this: <add algorithmType="System.Security.Cryptography.SHA1Managed, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=blahblahblah" saltEnabled="true" type="Microsoft.Practices.EnterpriseLibrary.Security.Cryptography.HashAlgorithmProvider, Microsoft.Practices.EnterpriseLibrary.Security.Cryptography, Version=3.0.0.0, Culture=neutral, PublicKeyToken=daahblahdahdah" name="MYHasher" /> So for a given password, I get back and store in the database a 48 byte salted sha1. I assume the last 8 bytes are the salt. I have tried to reproduce the hashing process in python by doing a sha1(salt + password) and sha1(password + salt) but I'm having no luck. My question to you: How are the public keys being used? How is the password rehashed using the salt. How is the salt created? (e.g., When I say saltEnabled="true", what extra magic happens?) I need specific details that don't just reference other .NET libraries, I'm looking for the actual operational logic that happens in the blackbox. Thanks!

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• Python PyQt Timer Firmata

  - by George Cullins

  Hello. I am pretty new to python and working with firmata I am trying to play around with an arduino . Here is what I want to happen: Set arduino up with an LED as a digital out Set potentiometer to analog 0 Set PyQt timer up to update potentiometer position in application Set a threshold in PyQt to turn LED on (Analog in has 1024bit resolution, so say 800 as the threshold) I am using this firmata library : Link Here is the code that I am having trouble with: import sys from PyQt4 import QtCore, QtGui from firmata import * # Arduino setup self.a = Arduino('COM3') self.a.pin_mode(13, firmata.OUTPUT) # Create timer self.appTimer = QtCore.QTimer(self) self.appTimer.start(100) self.appTimer.event(self.updateAppTimer()) def updateAppTimer(self): self.analogPosition = self.a.analog_read(self, 0) self.ui.lblPositionValue.setNum() I am getting the error message: Traceback (most recent call last): File "D:\Programming\Eclipse\IO Demo\src\control.py", line 138, in myapp = MainWindow() File "D:\Programming\Eclipse\IO Demo\src\control.py", line 56, in init self.appTimer.event(self.updateAppTimer()) File "D:\Programming\Eclipse\IO Demo\src\control.py", line 60, in updateAppTimer self.analogPosition = self.a.analog_read(self, 0) TypeError: analog_read() takes exactly 2 arguments (3 given) If I take 'self' out I get the same error message but that only 1 argument is given What is python doing implicitly that I am not aware of? Blockquote

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• Python dictionary formating

  - by None

  I made a python function to convert dictionaries to formatted strings. My goal was to have a function take a dictionary for input and turn it into a string that looked good. For example, something like "{'text':'Hello', 'blah':{'hi':'hello','hello':'hi'}}" would be turned into this: text: Hello blah: hi: hello hello: hi This is the code I wrote: indent = 0 def format_dict(d): global indent res = "" for key in d: res += (" " * indent) + key + ":\n" if not type(d[key]) == type({}): res += (" " * (indent + 1)) + d[key] + "\n" else: indent += 1 res += format_dict(d[key]) indent -= 1 return res #test print format_dict({'key with text content':'some text', 'key with dict content': {'cheese': 'text', 'item':{'Blah': 'Hello'}}}) It works like a charm. It checks if the dictionary item is another dictionary, in which it process that, or something else, in which it would use that as the value. The problem is: I can't have a dictionary and a string together in a dictionary item. For example: if I wanted blah: hi hello: hello again there'd be no way to do it. Is there some way I could have something like a list item in a dictionary. Something like this "{'blah':{'hi', 'hello':'hello again'}}"? And if you provide a solution could you tell me how I would need to change my code (if it did require changes). Note: I am using python 2.5

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• maintaining a large list in python

  - by Oren

  I need to maintain a large list of python pickleable objects that will quickly execute the following algorithm: The list will have 4 pointers and can: Read\Write each of the 4 pointed nodes Insert new nodes before the pointed nodes Increase a pointer by 1 Pop nodes from the beginning of the list (without overlapping the pointers) Add nodes at the end of the list The list can be very large (300-400 MB), so it shouldnt be contained in the RAM. The nodes are small (100-200 bytes) but can contain various types of data. The most efficient way it can be done, in my opinion, is to implement some paging-mechanism. On the harddrive there will be some database of a linked-list of pages where in every moment up to 5 of them are loaded in the memory. On insertion, if some max-page-size was reached, the page will be splitted to 2 small pages, and on pointer increment, if a pointer is increased beyond its loaded page, the following page will be loaded instead. This is a good solution, but I don't have the time to write it, especially if I want to make it generic and implement all the python-list features. Using a SQL tables is not good either, since I'll need to implement a complex index-key mechanism. I tried ZODB and zc.blist, which implement a BTree based list that can be stored in a ZODB database file, but I don't know how to configure it so the above features will run in reasonable time. I don't need all the multi-threading\transactioning features. No one else will touch the database-file except for my single-thread program. Can anyone explain me how to configure the ZODB\zc.blist so the above features will run fast, or show me a different large-list implementation?

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• Producing an view of a text's revision history in Python

  - by hekevintran

  I have two versions of a piece of text and I want to produce an HTML view of its revision similar to what Google Docs or Stack Overflow displays. I need to do this in Python. I don't know what this technique is called but I assume that it has a name and hopefully there is a Python library that can do it. Version 1: William Henry "Bill" Gates III (born October 28, 1955)[2] is an American business magnate, philanthropist, and chairman[3] of Microsoft, the software company he founded with Paul Allen. Version 2: William Henry "Bill" Gates III (born October 28, 1955)[2] is a business magnate, philanthropist, and chairman[3] of Microsoft, the software company he founded with Paul Allen. He is American. The desired output: William Henry "Bill" Gates III (born October 28, 1955)[2] is an American business magnate, philanthropist, and chairman[3] of Microsoft, the software company he founded with Paul Allen. He is American. Using the diff command doesn't work because it tells me which lines are different but not which columns/words are different. $ echo 'William Henry "Bill" Gates III (born October 28, 1955)[2] is an American business magnate, philanthropist, and chairman[3] of Microsoft, the software company he founded with Paul Allen.' > oldfile $ echo 'William Henry "Bill" Gates III (born October 28, 1955)[2] is a business magnate, philanthropist, and chairman[3] of Microsoft, the software company he founded with Paul Allen. He is American.' > newfile $ diff -u oldfile newfile --- oldfile 2010-04-30 13:32:43.000000000 -0700 +++ newfile 2010-04-30 13:33:09.000000000 -0700 @@ -1 +1 @@ -William Henry "Bill" Gates III (born October 28, 1955)[2] is an American business magnate, philanthropist, and chairman[3] of Microsoft, the software company he founded with Paul Allen. +William Henry "Bill" Gates III (born October 28, 1955)[2] is a business magnate, philanthropist, and chairman[3] of Microsoft, the software company he founded with Paul Allen. He is American.' > oldfile

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• Classes, methods, and polymorphism in Python

  - by Morlock

  I made a module prototype for building complex timer schedules in python. The classe prototypes permit to have Timer objects, each with their waiting times, Repeat objects that group Timer and other Repeat objects, and a Schedule class, just for holding a whole construction or Timers and Repeat instances. The construction can be as complex as needed and needs to be flexible. Each of these three classes has a .run() method, permitting to go through the whole schedule. Whatever the Class, the .run() method either runs a timer, a repeat group for a certain number of iterations, or a schedule. Is this polymorphism-oriented approach sound or silly? What are other appropriate approaches I should consider to build such a versatile utility that permits to put all building blocks together in as complex a way as desired with simplicity? Thanks! Here is the module code: ##################### ## Importing modules from time import time, sleep ##################### ## Class definitions class Timer: """ Timer object with duration. """ def __init__(self, duration): self.duration = duration def run(self): print "Waiting for %i seconds" % self.duration wait(self.duration) chime() class Repeat: """ Repeat grouped objects for a certain number of repetitions. """ def __init__(self, objects=[], rep=1): self.rep = rep self.objects = objects def run(self): print "Repeating group for %i times" % self.rep for i in xrange(self.rep): for group in self.objects: group.run() class Schedule: """ Groups of timers and repetitions. Maybe redundant with class Repeat. """ def __init__(self, schedule=[]): self.schedule = schedule def run(self): for group in self.schedule: group.run() ######################## ## Function definitions def wait(duration): """ Wait a certain number of seconds. """ time_end = time() + float(duration) #uncoment for minutes# * 60 time_diff = time_end - time() while time_diff > 0: sleep(1) time_diff = time_end - time() def chime(): print "Ding!"

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• Python: fetching SVG file using urllib is returning binary when I need ASCII

  - by Drew Dara-Abrams

  I'm using urllib (in Python) to fetch an SVG file: import urllib urllib.urlopen('http://alpha.vectors.cloudmade.com/BC9A493B41014CAABB98F0471D759707/-122.2487,37.87588,-122.265823,37.868054?styleid=1&viewport=400x231').read() which produces output of the sort: xb6\xf6\x00\xb3\xfb2\xff\xda\xc5\xf2\xc2\x14\xef\xcd\x82\x0b\xdbU\xb0\x81\xcaF\xd8\x1a\xf6\xdf[i)\xba\xcf\x80\xab\xd6\x8c\xe3l_\xe7\n\xed2,\xbdm\xa0_|\xbb\x12\xff\xb6\xf8\xda\xd9\xc3\xd9\t\xde\x9a\xf8\xae\xb3T\xa3\r`\x8a\x08!T\xfb8\x92\x95\x0c\xdd\x8b!\x02P\xea@\x98\x1c^\xc7\xda\\\xec\xe3\xe1\xbe,0\xcd\xbeZ~\x92\xb3\xfa\xdd\xfcbyu\xb8\x83\xbb\xbdS\x0f\x82\x0b\xfe\xf5_\xdawn\xff\xef_\xff\xe5\xfa\x1f?\xbf\xffoZ\x0f\x8b\xbfV\xf4\x04\x00' when I was expecting more like this: <?xml version='1.0' encoding='UTF-8'?> <svg xmlns="http://www.w3.org/2000/svg" xmlns:cm="http://cloudmade.com/" width="400" height="231"> <rect width="100%" height="100%" fill="#eae8dd" opacity="1"/> <g transform="scale(0.209849975856)"> <g transform="translate(13610569, 4561906)" flood-opacity="0.1" flood-color="grey"> <path d="M -13610027.720000000670552 -4562403.660000000149012 I guess this is an issue of binary vs. ASCII. Can anyone help me (a Python newbie) with the appropriate conversion so that I can get on with parsing and manipulating the SVG code?

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• python - tkinter - update label from variable

  - by Tom

  I wrote a python script that does some stuff to generate and then keep changing some text stored as a string variable. This works, and I can print the string each time it gets changed. Problems have arisen while trying to display that output in a GUI (just as a basic label) using tkinter. I can get the label to display the string for the first time... but it never updates. This is really the first time I have tried to use tkinter, so it's likely I'm making a foolish error. What I've got looks logical to me, but I'm evidently going wrong somewhere! from tkinter import * outputText = 'Ready' counter = int(0) root = Tk() root.maxsize(400, 400) var = StringVar() l = Label(root, textvariable=var, anchor=NW, justify=LEFT, wraplength=398) l.pack() var.set(outputText) while True: counter = counter + 1 #do some stuff that generates string as variable 'result' outputText = result #do some more stuff that generates new string as variable 'result' outputText = result #do some more stuff that generates new string as variable 'result' outputText = result if counter == 5: break root.mainloop() I also tried: from tkinter import * outputText = 'Ready' counter = int(0) root = Tk() root.maxsize(400, 400) var = StringVar() l = Label(root, textvariable=var, anchor=NW, justify=LEFT, wraplength=398) l.pack() var.set(outputText) while True: counter = counter + 1 #do some stuff that generates string as variable 'result' outputText = result var.set(outputText) #do some more stuff that generates new string as variable 'result' outputText = result var.set(outputText) #do some more stuff that generates new string as variable 'result' outputText = result var.set(outputText) if counter == 5: break root.mainloop() In both cases, the label will show 'Ready' but won't update to change that to the strings as they're generated later. After a fair bit of googling and looking through answers on this site, I thought the solution might be to use update_idletasks - I tried putting that in after each time the variable was changed, but it didn't help. It also seems possible I am meant to be using trace and callback somehow to make all this work...but I can't get my head around how that works (I tried, but didn't manage to make anything that even looked like it would do something, let alone actually worked). I'm still very new to both python and especially tkinter, so, any help much appreciated but please spell it out for me if you can :)

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• Starting out NLP - Python + large data set

  - by pencilNero

  Hi, I've been wanting to learn python and do some NLP, so have finally gotten round to starting. Downloaded the english wikipedia mirror for a nice chunky dataset to start on, and have been playing around a bit, at this stage just getting some of it into a sqlite db (havent worked with dbs in the past unfort). But I'm guessing sqlite is not the way to go for a full blown nlp project(/experiment :) - what would be the sort of things I should look at ? HBase (.. and hadoop) seem interesting, i guess i could run then im java, prototype in python and maybe migrate the really slow bits to java... alternatively just run Mysql.. but the dataset is 12gb, i wonder if that will be a problem? Also looked at lucene, but not sure how (other than breaking the wiki articles into chunks) i'd get that to work.. What comes to mind for a really flexible NLP platform (i dont really know at this stage WHAT i want to do.. just want to learn large scale lang analysis tbh) ? Many thanks.

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• Create a VPN with Python

  - by user213060

  I want to make a device "tunnel box" that you plug an input ethernet line, and an output ethernet line, and all the traffic that goes through it gets modified in a special way. This is similar to how a firewall, IDS, VPN, or similar boxes are connected inline in a network. I think you can just assume that I am writing a custom VPN in Python for the purpose of this question: LAN computer <--\ LAN computer <---> [LAN switch] <--> ["tunnel box"] <--> [internet modem] <--> LAN computer <--/ My question is, what is a good way to program this "tunnel box" from python? My application needs to see TCP flows at the network layer, not as individual ethernet frames. Non-TCP/IP traffic such as ICPM and other types should just be passed through. Example Twisted-like Code for my "tunnel box" tunnel appliance: from my_code import special_data_conversion_function class StreamInterceptor(twisted.Protocol): def dataReceived(self,data): data=special_data_conversion_function(data) self.outbound_connection.send(data) My initial guesses: TUN/TAP with twisted.pair.tuntap.py - Problem: This seems to only work at the ethernet frame level, not like my example? Socks proxy - Problem: Not transparent as in my diagram. Programs have to be specifically setup for it. Thanks!

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• using python 'with' statement with iterators?

  - by Stephen

  Hi, I'm using Python 2.5. I'm trying to use this 'with' statement. from __future__ import with_statement a = [] with open('exampletxt.txt','r') as f: while True: a.append(f.next().strip().split()) print a The contents of 'exampletxt.txt' are simple: a b In this case, I get the error: Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/tmp/python-7036sVf.py", line 5, in <module> a.append(f.next().strip().split()) StopIteration And if I replace f.next() with f.read(), it seems to be caught in an infinite loop. I wonder if I have to write a decorator class that accepts the iterator object as an argument, and define an __exit__ method for it? I know it's more pythonic to use a for-loop for iterators, but I wanted to implement a while loop within a generator that's called by a for-loop... something like def g(f): while True: x = f.next() if test1(x): a = x elif test2(x): b = f.next() yield [a,x,b] a = [] with open(filename) as f: for x in g(f): a.append(x)

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• Python API for VirtualBox

  - by jessica

  I have made a command-line interface for virtualbox such that the virtualbox can be controlled from a remote machine. now I am trying to implement the commmand-line interface using python virtualbox api. For that I have downloaded the pyvb package (python api documentation shows functions that can be used for implementing this under pyvb package). but when I give pyvb.vb.VB.startVM(instance of VB class,pyvb.vm.vbVM) SERVER SIDE CODE IS from pyvb.constants import * from pyvb.vm import * from pyvb.vb import * import xpcom import pyvb import os import socket import threading class ClientThread ( threading.Thread ): # Override Thread's init method to accept the parameters needed: def init ( self, channel, details ): self.channel = channel self.details = details threading.Thread.__init__ ( self ) def run ( self ): print 'Received connection:', self.details [ 0 ] while 1: s= self.channel.recv ( 1024 ) if(s!='end'): if(s=='start'): v=VB() pyvb.vb.VB.startVM(v,pyvb.vm.vbVM) else: self.channel.close() break print 'Closed connection:', self.details [ 0 ] server = socket.socket ( socket.AF_INET, socket.SOCK_STREAM ) server.bind ( ( '127.0.0.1', 2897 ) ) server.listen ( 5 ) while True: channel, details = server.accept() ClientThread ( channel, details ).start() it shows an error Exception in thread Thread-1: Traceback (most recent call last): File "/usr/lib/python2.5/threading.py", line 486, in __bootstrap_inner self.run() File "news.py", line 27, in run pyvb.vb.VB.startVM(v,pyvb.vm.vbVM.getUUID(m)) File "/usr/lib/python2.5/site-packages/pyvb-0.0.2-py2.5.egg/pyvb/vb.py", line 65, in startVM cmd='%s %s'%(VB_COMMAND_STARTVM, vm.getUUID()) AttributeError: 'str' object has no attribute 'getUUID'

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• How do you invoke a python script inside a jar file using python ?

  - by Trevor

  I'm working on an application that intersperses a bunch of jython and java code. Due to the nature of the program (using wsadmin) we are really restricted to Python 2.1 We currently have a jar containing both java source and .py modules. The code is currently invoked using java, but I'd like to remove this in favor of migrating as much functionality as possible to jython. The problem I have is that I want to either import or execute python modules inside the existing jar file from a calling jython script. I've tried a couple of different ways without success. My directory structure looks like: application.jar |-- com |--example |-- action |-- MyAction.class |-- pre_myAction.py The 1st approach I tried was to do imports from the jar. I added the jar to my sys.path and tried to import the module using both import com.example.action.myAction and import myAction. No success however, even when I put init.py files into the directory at each level. The 2nd approach I tried was to load the resource using the java class. So I wrote the below code: import sys import os import com.example.action.MyAction as MyAction scriptName = str(MyAction.getResource('/com/example/action/myAction.py')) scriptStr = MyAction.getResourceAsStream('/com/example/action/myAction.py') try: print execfile(scriptStr) except: print "failed 1" try: print execfile(scriptName) except: print "failed 2" Both of these failed. I'm at a bit of a loss now as to how I should proceed. Any ideas ? cheers, Trevor

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• Python doctest error

  - by user74283

  Hi I recently started experimenting with python currently reading "Think like a computer scientist: Learning python v2nd edition" I have been having some trouble with doctest. I use a windows 7 machine and Eclipse IDE with pydev. My question is when i run the script below i get the error below. Said script is below the the error message Traceback (most recent call last): File "C:\Users\shaytac\PythonProjects\test.py", line 21, in doctest.testmod() File "C:\Python26\lib\doctest.py", line 1829, in testmod for test in finder.find(m, name, globs=globs, extraglobs=extraglobs): File "C:\Python26\lib\doctest.py", line 852, in find self._find(tests, obj, name, module, source_lines, globs, {}) File "C:\Python26\lib\doctest.py", line 906, in _find globs, seen) File "C:\Python26\lib\doctest.py", line 894, in _find test = self._get_test(obj, name, module, globs, source_lines) File "C:\Python26\lib\doctest.py", line 978, in _get_test filename, lineno) File "C:\Python26\lib\doctest.py", line 597, in get_doctest return DocTest(self.get_examples(string, name), globs, File "C:\Python26\lib\doctest.py", line 611, in get_examples return [x for x in self.parse(string, name) File "C:\Python26\lib\doctest.py", line 573, in parse self._parse_example(m, name, lineno) File "C:\Python26\lib\doctest.py", line 631, in _parse_example self._check_prompt_blank(source_lines, indent, name, lineno) File "C:\Python26\lib\doctest.py", line 718, in _check_prompt_blank line[indent:indent+3], line)) ValueError: line 2 of the docstring for main.compare lacks blank after : 'compare(5, 4) ' def compare(a, b): """ >>>compare(5, 4) 1 >>>compare(7, 7) 0 >>>compare(2, 3) -1 >>>compare(42, 1) 1 """ if a > b : return 1 if a == b : return 0 if a < b : return -1 if __name__ == '__main__': import doctest doctest.testmod()

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• Python Pre-testing for exceptions when coverage fails

  - by Tal Weiss

  I recently came across a simple but nasty bug. I had a list and I wanted to find the smallest member in it. I used Python's built-in min(). Everything worked great until in some strange scenario the list was empty (due to strange user input I could not have anticipated). My application crashed with a ValueError (BTW - not documented in the official docs). I have very extensive unit tests and I regularly check coverage to avoid surprises like this. I also use Pylint (everything is integrated in PyDev) and I never ignore warnings, yet I failed to catch this bug before my users did. Is there anything I can change in my methodology to avoid these kind of runtime errors? (which would have been caught at compile time in Java / C#?). I'm looking for something more than wrapping my code with a big try-except. What else can I do? How many other build in Python functions are hiding nasty surprises like this???

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• python: nonblocking subprocess, check stdout

  - by Will Cavanagh

  Ok so the problem I'm trying to solve is this: I need to run a program with some flags set, check on its progress and report back to a server. So I need my script to avoid blocking while the program executes, but I also need to be able to read the output. Unfortunately, I don't think any of the methods available from Popen will read the output without blocking. I tried the following, which is a bit hack-y (are we allowed to read and write to the same file from two different objects?) import time import subprocess from subprocess import * with open("stdout.txt", "wb") as outf: with open("stderr.txt", "wb") as errf: command = ['Path\\To\\Program.exe', 'para', 'met', 'ers'] p = subprocess.Popen(command, stdout=outf, stderr=errf) isdone = False while not isdone : with open("stdout.txt", "rb") as readoutf: #this feels wrong for line in readoutf: print(line) print("waiting...\\r\\n") if(p.poll() != None) : done = True time.sleep(1) output = p.communicate()[0] print(output) Unfortunately, Popen doesn't seem to write to my file until after the command terminates. Does anyone know of a way to do this? I'm not dedicated to using python, but I do need to send POST requests to a server in the same script, so python seemed like an easier choice than, say, shell scripting. Thanks! Will

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• Endless problems with a very simple python subprocess.Popen task

  - by Thomas

  I'd like python to send around a half-million integers in the range 0-255 each to an executable written in C++. This executable will then respond with a few thousand integers. Each on one line. This seems like it should be very simple to do with subprocess but i've had endless troubles. Right now im testing with code: // main() u32 num; std::cin >> num; u8* data = new u8[num]; for (u32 i = 0; i < num; ++i) std::cin >> data[i]; // test output / spit it back out for (u32 i = 0; i < num; ++i) std::cout << data[i] << std::endl; return 0; Building an array of strings ("data"), each like "255\n", in python and then using: output = proc.communicate("".join(data))[0] ...doesn't work (says stdin is closed, maybe too much at one time). Neither has using proc.stdin and proc.stdout worked. This should be so very simple, but I'm getting constant exceptions, and/or no output data returned to me. My Popen is currently: proc = Popen('aux/test_cpp_program', stdin=PIPE, stdout=PIPE, bufsize=1) Advise me before I pull my hair out. ;)

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• Getting all new messages from a Maildir in python

  - by Jesper

  I have a mail dir: foo@foo:~/Maildir$ ls -l total 288 drwx------ 2 foo foo 155648 2010-04-19 15:19 cur -rw------- 1 foo foo 440 2010-03-20 08:50 dovecot.index.log -rw------- 1 foo foo 112 2010-03-20 08:49 dovecot-uidlist -rw------- 1 foo foo 8 2010-03-20 08:49 dovecot-uidvalidity -rw------- 1 foo foo 0 2010-03-20 08:49 dovecot-uidvalidity.4ba48c0e drwx------ 2 foo foo 114688 2010-04-19 16:07 new drwx------ 2 foo foo 4096 2010-04-19 16:07 tmp And in python I'm trying to get all new messages (Python 2.6.5rc2). First, getting "Maildir" works: >>> import mailbox >>> md = mailbox.Maildir('/home/foo/Maildir') >>> md.iterkeys().next() '1269924477.Vfc01I4249fM708004.foo' But how do I access "Maildir/new"? This does not work: >>> md = mailbox.Maildir('/home/foo/Maildir/new') >>> md.iterkeys().next() Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/python2.6/mailbox.py", line 346, in iterkeys self._refresh() File "/usr/lib/python2.6/mailbox.py", line 467, in _refresh for entry in os.listdir(subdir_path): OSError: [Errno 2] No such file or directory: '/home/foo/Maildir/new/new' >>> Any ideas?

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• Help me find an appropriate ruby/python parser generator

  - by Geo

  The first parser generator I've worked with was Parse::RecDescent, and the guides/tutorials available for it were great, but the most useful feature it has was it's debugging tools, specifically the tracing capabilities ( activated by setting $RD_TRACE to 1 ). I am looking for a parser generator that can help you debug it's rules. The thing is, it has to be written in python or in ruby, and have a verbose mode/trace mode or very helpful debugging techniques. Does anyone know such a parser generator ? EDIT: when I said debugging, I wasn't referring to debugging python or ruby. I was referring to debugging the parser generator, see what it's doing at every step, see every char it's reading, rules it's trying to match. Hope you get the point. BOUNTY EDIT: to win the bounty, please show a parser generator framework, and illustrate some of it's debugging features. I repeat, I'm not interested in pdb, but in parser's debugging framework. Also, please don't mention treetop. I'm not interested in it.

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• Replicating SQL's 'Join' in Python

  - by Daniel Mathews

  I'm in the process of trying to switch from R to Python (mainly issues around general flexibility). With Numpy, matplotlib and ipython, I've am able to cover all my use cases save for merging 'datasets'. I would like to simulate SQL's join by clause (inner, outer, full) purely in python. R handles this with the 'merge' function. I've tried the numpy.lib.recfunctions join_by, but it critical issues with duplicates along the 'key': join_by(key, r1, r2, jointype='inner', r1postfix='1', r2postfix='2', defaults=None, usemask=True, asrecarray=False) Join arrays r1 and r2 on key key. The key should be either a string or a sequence of string corresponding to the fields used to join the array. An exception is raised if the key field cannot be found in the two input arrays. Neither r1 nor r2 should have any duplicates along key: the presence of duplicates will make the output quite unreliable. Note that duplicates are not looked for by the algorithm. source: http://presbrey.mit.edu:1234/numpy.lib.recfunctions.html Any pointers or help will be most appreciated!

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• Converting python collaborative filtering code to use Map Reduce

  - by Neil Kodner

  Using Python, I'm computing cosine similarity across items. given event data that represents a purchase (user,item), I have a list of all items 'bought' by my users. Given this input data (user,item) X,1 X,2 Y,1 Y,2 Z,2 Z,3 I build a python dictionary {1: ['X','Y'], 2 : ['X','Y','Z'], 3 : ['Z']} From that dictionary, I generate a bought/not bought matrix, also another dictionary(bnb). {1 : [1,1,0], 2 : [1,1,1], 3 : [0,0,1]} From there, I'm computing similarity between (1,2) by calculating cosine between (1,1,0) and (1,1,1), yielding 0.816496 I'm doing this by: items=[1,2,3] for item in items: for sub in items: if sub >= item: #as to not calculate similarity on the inverse sim = coSim( bnb[item], bnb[sub] ) I think the brute force approach is killing me and it only runs slower as the data gets larger. Using my trusty laptop, this calculation runs for hours when dealing with 8500 users and 3500 items. I'm trying to compute similarity for all items in my dict and it's taking longer than I'd like it to. I think this is a good candidate for MapReduce but I'm having trouble 'thinking' in terms of key/value pairs. Alternatively, is the issue with my approach and not necessarily a candidate for Map Reduce?

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• Decoding tcp packets using python

  - by mikip

  Hello I am trying to decode data received over a tcp connection. The packets are small, no more than 100 bytes. However when there is a lot of them I receive some of the the packets joined together. Is there a way to prevent this. I am using python I have tried to separate the packets, my source is below. The packets start with STX byte and end with ETX bytes, the byte following the STX is the packet length, (packet lengths less than 5 are invalid) the checksum is the last bytes before the ETX def decode(data): while True: start = data.find(STX) if start == -1: #no stx in message pkt = '' data = '' break #stx found , next byte is the length pktlen = ord(data[1]) #check message ends in ETX (pktken -1) or checksum invalid if pktlen < 5 or data[pktlen-1] != ETX or checksum_valid(data[start:pktlen]) == False: print "Invalid Pkt" data = data[start+1:] continue else: pkt = data[start:pktlen] data = data[pktlen:] break return data , pkt I use it like this #process reports try: data = sock.recv(256) except: continue else: while data: data, pkt = decode(data) if pkt: process(pkt) Also if there are multiple packets in the data stream, is it best to return the packets as a collection of lists or just return the first packet I am not that familiar with python, only C, is this method OK. Any advice would be most appreciated. Thanks in advance Thanks

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• Reading UTF-8 XML and writing it to a file with Python

  - by Harri

  I'm trying to parse UTF-8 XML file and save some parts of it to another file. Problem is, that this is my first Python script ever and I'm totally confused about the character encoding problems I'm finding. My script fails immediately when it tries to write non-ascii character to a file, but it can print it to command prompt (at least in some level) Here's the XML (from the parts that matter at least, it's a *.resx file which contains UI strings) <?xml version="1.0" encoding="utf-8"?> <root> <resheader name="foo"> <value>bar</value> </resheader> <data name="lorem" xml:space="preserve"> <value>ipsum öä</value> </data> </root> And here's my python script from xml.dom.minidom import parse names = [] values = [] def getStrings(path): dom = parse(path) data = dom.getElementsByTagName("data") for i in range(len(data)): name = data[i].getAttribute("name") names.append(name) value = data[i].getElementsByTagName("value") values.append(value[0].firstChild.nodeValue.encode("utf-8")) def writeToFile(): with open("uiStrings-fi.py", "w") as f: for i in range(len(names)): line = names[i] + '="'+ values[i] + '"' #varName='varValue' f.write(line) f.write("\n") getStrings("ResourceFile.fi-FI.resx") writeToFile() And here's the traceback: Traceback (most recent call last): File "GenerateLanguageFiles.py", line 24, in writeToFile() File "GenerateLanguageFiles.py", line 19, in writeToFile line = names[i] + '="'+ values[i] + '"' #varName='varValue' UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 2: ordinal not in ran ge(128) How should I fix my script so it would read and write UTF-8 characters properly? The files I'm trying to generate would be used in test automation with Robots Framework.

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• Python: puzzling behaviour inside httplib

  - by Anna

  I have added one line ( import pdb; pdb.set_trace() ) to httplib's HTTPConnection.putheader, so I can see what's going on inside. httplib.py, line 489: def putheader(self, header, value): """Send a request header line to the server. For example: h.putheader('Accept', 'text/html') """ import pdb; pdb.set_trace() if self.__state != _CS_REQ_STARTED: raise CannotSendHeader() str = '%s: %s' % (header, value) self._output(str) then ran this from the interpreter import urllib2 urllib2.urlopen('http://www.ioerror.us/ip/headers') ... and as expected PDB kicks in: > c:\python26\lib\httplib.py(858)putheader() -> if self.__state != _CS_REQ_STARTED: (Pdb) in PDB I have the luxury of evaluating expressions on the fly, so I have tried to enter self.__state: (Pdb) self.__state *** AttributeError: HTTPConnection instance has no attribute '__state' Alas, there is no __state of this instance. However when I enter step, the debugger gets past the if self.__state != _CS_REQ_STARTED: line without a problem. Why is this happening? If the self.__state doesn't exist python would have to raise an exception as it did when I entered the expression. Python version: 2.6.4 on win32

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• Base class deleted before subclass during python __del__ processing

  - by Oddthinking

  Context I am aware that if I ask a question about Python destructors, the standard argument will be to use contexts instead. Let me start by explaining why I am not doing that. I am writing a subclass to logging.Handler. When an instance is closed, it posts a sentinel value to a Queue.Queue. If it doesn't, a second thread will be left running forever, waiting for Queue.Queue.get() to complete. I am writing this with other developers in mind, so I don't want a failure to call close() on a handler object to cause the program to hang. Therefore, I am adding a check in __del__() to ensure the object was closed properly. I understand circular references may cause it to fail in some circumstances. There's not a lot I can do about that. Problem Here is some simple example code: explicit_delete = True class Base: def __del__(self): print "Base class cleaning up." class Sub(Base): def __del__(self): print "Sub-class cleaning up." Base.__del__(self) x = Sub() if explicit_delete: del x print "End of thread" When I run this I get, as expected: Sub-class cleaning up. Base class cleaning up. End of thread If I set explicit_delete to False in the first line, I get: End of thread Sub-class cleaning up. Exception AttributeError: "'NoneType' object has no attribute '__del__'" in <bound method Sub.__del__ of <__main__.Sub instance at 0x00F0B698>> ignored It seems the definition of Base is removed before the x._del_() is called. The Python Documentation on _del_() warns that the subclass needs to call the base-class to get a clean deletion, but here that appears to be impossible. Can you see where I made a bad step?

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