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• python crc32 woes

  - by lazyr

  I'm writing a python program to extract data from the middle of a 6 GB bz2 file. A bzip2 file is made up of independently decryptable blocks of data, so I only need to find a block (they are delimited by magic bits), then create a temporary one-block bzip2 file from it in memory, and finally pass that to the bz2.decompress function. Easy, no? The bzip2 format has a crc32 checksum for the file at the end. No problem, binascii.crc32 to the rescue. But wait. The data to be checksummed does not necessarily end on a byte boundary, and the crc32 function operates on a whole number of bytes. My plan: use the binascii.crc32 function on all but the last byte, and then a function of my own to update the computed crc with the last 1-7 bits. But hours of coding and testing has left me bewildered, and my puzzlement can be boiled down to this question: how come crc32("\x00") is not 0x00000000? Shouldn't it be, according to the wikipedia article? You start with 0b00000000 and pad with 32 0's, then do polynomial division with 0x04C11DB7 until there are no ones left in the first 8 bits, which is immediately. Your last 32 bits is the checksum, and how can that not be all zeroes? I've searched google for answers and looked at the code of several crc32 implementations without finding any clue to why this is so.

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• Efficient way to maintain a sorted list of access counts in Python

  - by David

  Let's say I have a list of objects. (All together now: "I have a list of objects.") In the web application I'm writing, each time a request comes in, I pick out up to one of these objects according to unspecified criteria and use it to handle the request. Basically like this: def handle_request(req): for h in handlers: if h.handles(req): return h return None Assuming the order of the objects in the list is unimportant, I can cut down on unnecessary iterations by keeping the list sorted such that the most frequently used (or perhaps most recently used) objects are at the front. I know this isn't something to be concerned about - it'll make only a miniscule, undetectable difference in the app's execution time - but debugging the rest of the code is driving me crazy and I need a distraction :) so I'm asking out of curiosity: what is the most efficient way to maintain the list in sorted order, descending, by the number of times each handler is chosen? The obvious solution is to make handlers a list of (count, handler) pairs, and each time a handler is chosen, increment the count and resort the list. def handle_request(req): for h in handlers[:]: if h[1].handles(req): h[0] += 1 handlers.sort(reverse=True) return h[1] return None But since there's only ever going to be at most one element out of order, and I know which one it is, it seems like some sort of optimization should be possible. Is there something in the standard library, perhaps, that is especially well-suited to this task? Or some other data structure? (Even if it's not implemented in Python) Or should/could I be doing something completely different?

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• Why can't I handle a KeyboardInterrupt in python?

  - by Josh

  I'm writing python 2.6.6 code on windows that looks like this: try: dostuff() except KeyboardInterrupt: print "Interrupted!" except: print "Some other exception?" finally: print "cleaning up...." print "done." dostuff() is a function that loops forever, reading a line at a time from an input stream and acting on it. I want to be able to stop it and clean up when I hit ctrl-c. What's happening instead is that the code under except KeyboardInterrupt: isn't running at all. The only thing that gets printed is "cleaning up...", and then a traceback is printed that looks like this: Traceback (most recent call last): File "filename.py", line 119, in <module> print 'cleaning up...' KeyboardInterrupt So, exception handling code is NOT running, and the traceback claims that a KeyboardInterrupt occurred during the finally clause, which doesn't make sense because hitting ctrl-c is what caused that part to run in the first place! Even the generic except: clause isn't running. EDIT: Based on the comments, I replaced the contents of the try: block with sys.stdin.read(). The problem still occurs exactly as described, with the first line of the finally: block running and then printing the same traceback.

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• Very simple python functions takes spends long time in function and not subfunctions

  - by John Salvatier

  I have spent many hours trying to figure what is going on here. The function 'grad_logp' in the code below is called many times in my program, and cProfile and runsnakerun the visualize the results reveals that the function grad_logp spends about .00004s 'locally' every call not in any functions it calls and the function 'n' spends about .00006s locally every call. Together these two times make up about 30% of program time that I care about. It doesn't seem like this is function overhead as other python functions spend far less time 'locally' and merging 'grad_logp' and 'n' does not make my program faster, but the operations that these two functions do seem rather trivial. Does anyone have any suggestions on what might be happening? Have I done something obviously inefficient? Am I misunderstanding how cProfile works? def grad_logp(self, variable, calculation_set ): p = params(self.p,self.parents) return self.n(variable, self.p) def n (self, variable, p ): gradient = self.gg(variable, p) return np.reshape(gradient, np.shape(variable.value)) def gg(self, variable, p): if variable is self: gradient = self._grad_logps['x']( x = self.value, **p) else: gradient = __builtin__.sum([self._pgradient(variable, parameter, value, p) for parameter, value in self.parents.iteritems()]) return gradient

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• Python re module becomes 20 times slower when called on greater than 101 different regex

  - by Wiil

  My problem is about parsing log files and removing variable parts on each lines to be able to group them. For instance: s = re.sub(r'(?i)User [_0-9A-z]+ is ', r"User .. is ", s) s = re.sub(r'(?i)Message rejected because : (.*?) \(.+\)', r'Message rejected because : \1 (...)', s) I have about 120+ matching rules like those above. I have found no performances issues while searching successively on 100 different regex. But a huge slow down comes when applying 101 regex. Exact same behavior happens when replacing my rules set by for a in range(100): s = re.sub(r'(?i)caught here'+str(a)+':.+', r'( ... )', s) Got 20 times slower when putting range(101) instead. # range(100) % ./dashlog.py file.bz2 == Took 2.1 seconds. == # range(101) % ./dashlog.py file.bz2 == Took 47.6 seconds. == Why such thing is happening ? And is there any known workaround ? (Happens on Python 2.6.6/2.7.2 on Linux/Windows.)

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• Dictionaries with more than one key per value in Python

  - by nickname

  I am attempting to create a nice interface to access a data set where each value has several possible keys. For example, suppose that I have both a number and a name for each value in the data set. I want to be able to access each value using either the number OR the name. I have considered several possible implementations: Using two separate dictionaries, one for the data values organized by number, and one for the data values organized by name. Simply assigning two keys to the same value in a dictionary. Creating dictionaries mapping each name to the corresponding number, and vice versa Attempting to create a hash function that maps each name to a number, etc. (related to the above) Creating an object to encapsulate all three pieces of data, then using one key to map dictionary keys to the objects and simply searching the dictionary to map the other key to the object. None of these seem ideal. The first seems ugly and unmaintainable. The second also seems fragile. The third/fourth seem plausible, but seem to require either much manual specification or an overly complex implementation. Finally, the fifth loses constant-time performance for one of the lookups. In C/C++, I believe that I would use pointers to reference the same piece of data from different keys. I know that the problem is rather similar to a database lookup problem by a non-key column, however, I would like (if possible), to maintain the approximate O(1) performance of Python dictionaries. What is the most Pythonic way to achieve this data structure?

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• Python for statement giving an Invalid Syntax error with list

  - by Cold Diamondz

  I have some code in which is throwing an error (I'm using repl.it) import random students = ['s1:0','s2:0','s3:0'] while True: print'\n'*50 print'Ticket Machine'.center(80) print'-'*80 print'1. Clear Student Ticket Values'.center(80) print'2. Draw Tickets'.center(80) menu = raw_input('-'*80+'\nChoose an Option: ') if menu == '1': print'\n'*50 print'CLEARED!' students = ['s1:0','s2:0','s3:0'] raw_input('Press enter to return to the main menu!') elif menu == '2': tickets = [] print'\n'*50 times = int(raw_input('How many tickets to draw? ') for a in students: for i in range(a.split(':')[1]): tickets.append(a.split(':')[0]) for b in range(1,times+1): print str(b) + '. ' + random.choice(tickets) else: print'\n'*50 print'That was not an option!' raw_input('Press enter to return to the main menu!') But it is throwing this error: File "<stdin>", line 19 for a in students: ^ SyntaxError: invalid syntax I am planning on using this in a class, but I can't use it until the bug is fixed, also, student names have been removed for privacy reasons.

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• Python: problem with tiny script to delete files

  - by Rosarch

  I have a project that used to be under SVN, but now I'm moving it to Mercurial, so I want to clear out all the .svn files. It's a little too big to do it by hand, so I decided to write a python script to do it. But it isn't working. def cleandir(dir_path): print "Cleaning %s\n" % dir_path toDelete = [] files = os.listdir(dir_path) for filedir in files: print "considering %s" % filedir # continue if filedir == '.' or filedir == '..': print "skipping %s" % filedir continue path = dir_path + os.sep + filedir if os.path.isdir(path): cleandir(path) else: print "not dir: %s" % path if 'svn' in filedir: toDelete.append(path) print "Files to be deleted:" for candidate in toDelete: print candidate print "Delete all? [y|n]" choice = raw_input() if choice == 'y': for filedir in toDelete: if os.path.isdir(filedir): os.rmdir(filedir) else: os.unlink(filedir) exit() if __name__ == "__main__": cleandir(dir) The print statements show that it's only "considering" the filedirs whose names start with ".". However, if I uncomment the continue statement, all the filedirs are "considered". Why is this? Or is there some other utility that already exists to recursively de-SVN-ify a directory tree?

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• Python coin-toss

  - by Andy

  i am new to Python, and i can't wrap my head around this. I have following function defined: def FlipCoins(num_flips): heads_rounds_won = 0 for i in range(10000): heads = 0 tails = 0 for j in range(num_flips): dice = random.randint(0,1) if dice==1: heads += 1 else: tails += 1 if heads > tails: heads_rounds_won += 1 return heads_rounds_won Here is what it should do (but apparently doesn't): flip a coin num_flip times, count heads and tails, and see if there are more heads than tails. If yes, increment head_rounds_won by 1. Repeat 10000 times. I would assume that head_rounds_won will approximate 5000 (50%). And it does that for odd numbers as input. For example, 3, 5 or 7 will produce about 50%. However, even numbers will produce much lower results, more like 34%. Small numbers especially, with higher even numbers, like for example 800, the difference to 50% is much narrower. Why is this the case? Shouldn't any input produce about 50% heads/tails?

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• Faster quadrature decoder loops with Python code

  - by Kelei

  I'm working with a BeagleBone Black and using Adafruit's IO Python library. Wrote a simple quadrature decoding function and it works perfectly fine when the motor runs at about 1800 RPM. But when the motor runs at higher speeds, the code starts missing some of the interrupts and the encoder counts start to accumulate errors. Do you guys have any suggestions as to how I can make the code more efficient or if there are functions which can cycle the interrupts at a higher frequency. Thanks, Kel Here's the code: # Define encoder count function def encodercount(term): global counts global Encoder_A global Encoder_A_old global Encoder_B global Encoder_B_old global error Encoder_A = GPIO.input('P8_7') # stores the value of the encoders at time of interrupt Encoder_B = GPIO.input('P8_8') if Encoder_A == Encoder_A_old and Encoder_B == Encoder_B_old: # this will be an error error += 1 print 'Error count is %s' %error elif (Encoder_A == 1 and Encoder_B_old == 0) or (Encoder_A == 0 and Encoder_B_old == 1): # this will be clockwise rotation counts += 1 print 'Encoder count is %s' %counts print 'AB is %s %s' % (Encoder_A, Encoder_B) elif (Encoder_A == 1 and Encoder_B_old == 1) or (Encoder_A == 0 and Encoder_B_old == 0): # this will be counter-clockwise rotation counts -= 1 print 'Encoder count is %s' %counts print 'AB is %s %s' % (Encoder_A, Encoder_B) else: #this will be an error as well error += 1 print 'Error count is %s' %error Encoder_A_old = Encoder_A # store the current encoder values as old values to be used as comparison in the next loop Encoder_B_old = Encoder_B # Initialize the interrupts - these trigger on the both the rising and falling GPIO.add_event_detect('P8_7', GPIO.BOTH, callback = encodercount) # Encoder A GPIO.add_event_detect('P8_8', GPIO.BOTH, callback = encodercount) # Encoder B # This is the part of the code which runs normally in the background while True: time.sleep(1)

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• Python logging in Django

  - by Jeff

  I'm developing a Django app, and I'm trying to use Python's logging module for error/trace logging. Ideally I'd like to have different loggers configured for different areas of the site. So far I've got all of this working, but one thing has me scratching my head. I have the root logger going to sys.stderr, and I have configured another logger to write to a file. This is in my settings.py file: sviewlog = logging.getLogger('MyApp.views.scans') view_log_handler = logging.FileHandler('C:\\MyApp\\logs\\scan_log.log') view_log_handler.setLevel(logging.INFO) view_log_handler.setFormatter(logging.Formatter('%(asctime)s %(name)-12s %(levelname)-8s %(message)s')) sviewlog.addHandler(view_log_handler) Seems pretty simple. Here's the problem, though: whatever I write to the sviewlog gets written to the log file twice. The root logger only prints it once. It's like addHandler() is being called twice. And when I put my code through a debugger, this is exactly what I see. The code in settings.py is getting executed twice, so two FileHandlers are created and added to the same logger instance. But why? And how do I get around this? Can anyone tell me what's going on here? I've tried moving the sviewlog logger/handler instantiation code to the file where it's used (since that actually seems like the appropriate place to me), but I have the same problem there. Most of the examples I've seen online use only the root logger, and I'd prefer to have multiple loggers.

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• Nested <ul><li> navigation menu using a recursive Python function

  - by Alex

  Hi. I want to render this data structure as an unordered list. menu = [ [1, 0], [2, 1], [3, 1], [4, 3], [5, 3], [6, 5], [7,1] ] [n][0] is the key [n][1] references the parent key The desired output is: <ul> <li>Node 1</li> <ul> <li>Node 2</li> <li>Node 3</li> <ul> <li>Node 4</li> <li>Node 5</li> <ul> <li>Node 6</li> </ul> </ul> <li>Node 7</li> </ul> </ul> I could probably do this without recursion but that would be no fun. Unfortunately, I am having problems putting it all together. I don't have much experience with recursion and this is proving to be very difficult for me to build and debug. What is the most efficient way to solve this problem in Python? Thanks!

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• List modification in Python

  - by user2945143

  We are given an algorithm to modify a list of numbers from 1 to 28. There are 5 steps in the algorithm. We have written functions for each step (all correct). We need to write a function that combines all 5 steps. The algorithm modifies the list to get a value. Each time you get a new value, you use the list created by the algorithm from the previous step. This is what we have gotten so far for the code: get_card_at_top_index(insert_top_to_bottom(triple_cut((move_joker_2( move_joker_1(deck)))))) When we run the code to generate the get_card_at_top_index, the first answer is correct. However, the rest are not. Instead of using from the new list, python uses the value that it generated from the last step. What did we do wrong? UPDATE: The other 5 codes passed the tests, they are correct. Code 1 (List) = list1 Code 2 (list1) = list2 Code 3 (list2) = list3 Code 4 (list3) = list4 Code 5 (list4) = list5 we generate a number from 5. We need to run the algorithm again to generate 25 more numbers. We will use list 5 start from step 1

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• Python-based password tracker (or dictionary)

  - by Arrieta

  Hello: Where we work we need to remember about 10 long passwords which need to change every so often. I would like to create a utility which can potentially save these passwords in an encrypted file so that we can keep track of them. I can think of some sort of dictionary passwd = {'host1':'pass1', 'host2':'pass2'}, etc, but I don't know what to do about encryption (absolutely zero experience in the topic). So, my question is really two questions: Is there a Linux-based utility which lets you do that? If you were to program it in Python, how would you go about it? A perk of approach two, would be for the software to update the ssh public keys after the password has been changed (you know the pain of updating ~15 tokens once you change your password). As it can be expected, I have zero control over the actual network configuration and the management of scp keys. I can only hope to provide a simple utility to me an my very few coworkers so that, if we need to, we can retrieve a password on demand. Cheers.

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• Image Gurus: Optimize my Python PNG transparency function

  - by ozone

  I need to replace all the white(ish) pixels in a PNG image with alpha transparency. I'm using Python in AppEngine and so do not have access to libraries like PIL, imagemagick etc. AppEngine does have an image library, but is pitched mainly at image resizing. I found the excellent little pyPNG module and managed to knock up a little function that does what I need: make_transparent.py pseudo-code for the main loop would be something like: for each pixel: if pixel looks "quite white": set pixel values to transparent otherwise: keep existing pixel values and (assuming 8bit values) "quite white" would be: where each r,g,b value is greater than "240" AND each r,g,b value is within "20" of each other This is the first time I've worked with raw pixel data in this way, and although works, it also performs extremely poorly. It seems like there must be a more efficient way of processing the data without iterating over each pixel in this manner? (Matrices?) I was hoping someone with more experience in dealing with these things might be able to point out some of my more obvious mistakes/improvements in my algorithm. Thanks!

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• python list Index out of range error

  - by dman762000

  I am working on a python tetris game that my proffessor assigned for the final project of a concepts of programming class. I have got just about everything he wanted to work on it at this point but I am having a slight problem with one part of it. Whenever I start moving pieces left and right I keep getting "index out of range error". This only happens when it is up against a piece. Here are the culprits that are giving me grief. def clearRight(block=None): global board, activeBlock, stackedBlocks isClear = True if(block == None): block = activeBlock if(block != None): for square in block['squares']: row = square[1] col = square[0]+1 if(col >= 0 and stackedBlocks[row][col] !=None): isClear=False return isClear def clearLeft(block=None): global board, activeBlock, stackedBlocks isClear = True if(block == None): block = activeBlock if(block != None): for square in block['squares']: row = square[1] col = square[0]-1 if(col >= 0 and stackedBlocks[row][col] !=None): isClear=False return isClear I am not looking to get anyone to fix it for me, I'm only looking for tips on how to fix it myself. Thanks in advance for any help that is given.

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• parse a special xml in python

  - by zhaojing

  I have s special xml file like below: <alarm-dictionary source="DDD" type="ProxyComponent"> <alarm code="402" severity="Alarm" name="DDM_Alarm_402"> <message>Database memory usage low threshold crossed</message> <description>dnKinds = database type = quality_of_service perceived_severity = minor probable_cause = thresholdCrossed additional_text = Database memory usage low threshold crossed </description> </alarm> ... </alarm-dictionary> I know in python, I can get the "alarm code", "severity" in tag alarm by: for alarm_tag in dom.getElementsByTagName('alarm'): if alarm_tag.hasAttribute('code'): alarmcode = str(alarm_tag.getAttribute('code')) And I can get the text in tag message like below: for messages_tag in dom.getElementsByTagName('message'): messages = "" for message_tag in messages_tag.childNodes: if message_tag.nodeType in (message_tag.TEXT_NODE, message_tag.CDATA_SECTION_NODE): messages += message_tag.data But I also want to get the value like dnkind(database), type(quality_of_service), perceived_severity(thresholdCrossed) and probable_cause(Database memory usage low threshold crossed ) in tag description. That is, I also want to parse the content in the tag in xml. Could anyone help me with this? Thanks a lot!

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• Python ctypes in_dll string assignment

  - by ackdesha

  I could use some help assigning to a global C variable in DLL using ctypes. The following is an example of what I'm trying: test.c contains the following #include <stdio.h> char name[60]; void test(void) { printf("Name is %s\n", name); } On windows (cygwin) I build a DLL (Test.dll) as follows: gcc -g -c -Wall test.c gcc -Wall -mrtd -mno-cygwin -shared -W1,--add-stdcall-alias -o Test.dll test.o When trying to modify the name variable and then calling the C test function using the ctypes interface I get the following... >>> from ctypes import * >>> dll = windll.Test >>> dll <WinDLL 'Test', handle ... at ...> >>> f = c_char_p.in_dll(dll, 'name') >>> f c_char_p(None) >>> f.value = 'foo' >>> f c_char_p('foo') >>> dll.test() Name is Name is 48+? 13 Why does the test function print garbage in this case?

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• Returning JSON from JavaScript to Python

  - by Chris Lacy

  I'm writing a simple App Engine app. I have a simple page that allows a user to move a marker on a Google map instance. Each time the user drops the marker, I want to return the long/lat to my Python app. function initialize() { ... // Init map var marker = new GMarker(center, {draggable: true}); GEvent.addListener(marker, "dragend", function() { // I want to return the marker.x/y to my app when this function is called .. }); } To my (admittedly limited) knowledge, I should be: 1). Returning a JSON structure with my required data in the listener callback above 2). In my webapp.RequestHandler Handler class, trying to retrieve the JSON structure during the post method. I would very much like to pass this JSOn data back to the app without causing a page reload (which is what has happened when I've used various post/form.submit methods so far). Can anyone provide me with some psuedo code or an example on how I might achieve what I'm after? Thanks.

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• Filtering string in Python

  - by Ecce_Homo

  I am making algorithm for checking the string (e-mail) - like "E-mail addres is valid" but their are rules. First part of e-mail has to be string that has 1-8 characters (can contain alphabet, numbers, underscore [ _ ]...all the parts that e-mail contains) and after @ the second part of e-mail has to have string that has 1-12 characters (also containing all legal expressions) and it has to end with top level domain .com EDIT email = raw_input ("Enter the e-mail address:") length = len (email) if length > 20 print "Address is too long" elif lenght < 5: print "Address is too short" if not email.endswith (".com"): print "Address doesn't contain correct domain ending" first_part = len (splitting[0]) second_part = len(splitting[1]) account = splitting[0] domain = splitting[1] for c in account: if c not in "abcdefghijklmopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_.": print "Invalid char", "->", c,"<-", "in account name of e-mail" for c in domain: if c not in "abcdefghijklmopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_.": print "Invalid char", "->", c,"<-", "in domain of e-mail" if first_part == 0: print "You need at least 1 character before the @" elif first_part> 8: print "The first part is too long" if second_part == 4: print "You need at least 1 character after the @" elif second_part> 16: print "The second part is too long" else: # if everything is fine return this print "E-mail addres is valid" EDIT: After reproting what is wrong with our input, now I need to make Python recognize valid address and return ("E-mail adress is valid") This is the best i can do with my knowledge....and we cant use regular expressions, teacher said we are going to learn them later.

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• Unit Testing Interfaces in Python

  - by Nicholas Mancuso

  I am currently learning python in preperation for a class over the summer and have gotten started by implementing different types of heaps and priority based data structures. I began to write a unit test suite for the project but ran into difficulties into creating a generic unit test that only tests the interface and is oblivious of the actual implementation. I am wondering if it is possible to do something like this.. suite = HeapTestSuite(BinaryHeap()) suite.run() suite = HeapTestSuite(BinomialHeap()) suite.run() What I am currently doing just feels... wrong (multiple inheritance? ACK!).. class TestHeap: def reset_heap(self): self.heap = None def test_insert(self): self.reset_heap() #test that insert doesnt throw an exception... for x in self.inseq: self.heap.insert(x) def test_delete(self): #assert we get the first value we put in self.reset_heap() self.heap.insert(5) self.assertEquals(5, self.heap.delete_min()) #harder test. put in sequence in and check that it comes out right self.reset_heap() for x in self.inseq: self.heap.insert(x) for x in xrange(len(self.inseq)): val = self.heap.delete_min() self.assertEquals(val, x) class BinaryHeapTest(TestHeap, unittest.TestCase): def setUp(self): self.inseq = range(99, -1, -1) self.heap = BinaryHeap() def reset_heap(self): self.heap = BinaryHeap() class BinomialHeapTest(TestHeap, unittest.TestCase): def setUp(self): self.inseq = range(99, -1, -1) self.heap = BinomialHeap() def reset_heap(self): self.heap = BinomialHeap() if __name__ == '__main__': unittest.main()

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• Python lists/arrays: disable negative indexing wrap-around

  - by wim

  While I find the negative number wraparound (i.e. A[-2] indexing the second-to-last element) extremely useful in many cases, there are often use cases I come across where it is more of an annoyance than helpful, and I find myself wishing for an alternate syntax to use when I would rather disable that particular behaviour. Here is a canned 2D example below, but I have had the same peeve a few times with other data structures and in other numbers of dimensions. import numpy as np A = np.random.randint(0, 2, (5, 10)) def foo(i, j, r=2): '''sum of neighbours within r steps of A[i,j]''' return A[i-r:i+r+1, j-r:j+r+1].sum() In the slice above I would rather that any negative number to the slice would be treated the same as None is, rather than wrapping to the other end of the array. Because of the wrapping, the otherwise nice implementation above gives incorrect results at boundary conditions and requires some sort of patch like: def ugly_foo(i, j, r=2): def thing(n): return None if n < 0 else n return A[thing(i-r):i+r+1, thing(j-r):j+r+1].sum() I have also tried zero-padding the array or list, but it is still inelegant (requires adjusting the lookup locations indices accordingly) and inefficient (requires copying the array). Am I missing some standard trick or elegant solution for slicing like this? I noticed that python and numpy already handle the case where you specify too large a number nicely - that is, if the index is greater than the shape of the array it behaves the same as if it were None.

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• python recursive iteration exceeding limit for tree implementation

  - by user3698027

  I'm implementing a tree dynamically in python. I have defined a class like this... class nodeobject(): def __init__(self,presentnode=None,parent=None): self.currentNode = presentnode self.parentNode = parent self.childs = [] I have a function which gets possible childs for every node from a pool def findchildren(node, childs): # No need to write the whole function on how it gets childs Now I have a recursive function that starts with the head node (no parent) and moves down the chain recursively for every node (base case being the last node having no children) def tree(dad,children): for child in children: childobject = nodeobject(child,dad) dad.childs.append(childobject) newchilds = findchildren(child, children) if len(newchilds) == 0: lastchild = nodeobject(newchilds,childobject) childobject.childs.append(lastchild) loopchild = copy.deepcopy(lastchild) while loopchild.parentNode != None: print "last child" else: tree(childobject,newchilds) The tree formation works for certain number of inputs only. Once the pool gets bigger, it results into "MAXIMUM RECURSION DEPTH EXCEEDED" I have tried setting the recursion limit with set.recursionlimit() and it doesn't work. THe program crashes. I want to implement a stack for recursion, can someone please help, I have gone no where even after trying for a long time ?? Also, is there any other way to fix this other than stack ?

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• How to parse multiple dates from a block of text in Python (or another language)

  - by mlissner

  I have a string that has several date values in it, and I want to parse them all out. The string is natural language, so the best thing I've found so far is dateutil. Unfortunately, if a string has multiple date values in it, dateutil throws an error: >>> s = "I like peas on 2011-04-23, and I also like them on easter and my birthday, the 29th of July, 1928" >>> parse(s, fuzzy=True) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/pymodules/python2.7/dateutil/parser.py", line 697, in parse return DEFAULTPARSER.parse(timestr, **kwargs) File "/usr/lib/pymodules/python2.7/dateutil/parser.py", line 303, in parse raise ValueError, "unknown string format" ValueError: unknown string format Any thoughts on how to parse all dates from a long string? Ideally, a list would be created, but I can handle that myself if I need to. I'm using Python, but at this point, other languages are probably OK, if they get the job done. PS - I guess I could recursively split the input file in the middle and try, try again until it works, but it's a hell of a hack.

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• Python/Sqlite app for web or desktop?

  - by ChrisC

  I am in the planning stages of rewriting an Access db I wrote several years ago in a full fledged program. I have very slight experience coding, but not enough to call myself a programmer by far. I'll definitely be learning as I go, so I'd like to keep everything as simple as possible. I've decided on Python and SQLite for my program, but I need help on my next decision. Here is my situation 1) It'll be a desktop program, run locally on each machine, all Windows 2) I want a nice looking GUI with colors, different shaped buttons, nice menus, lists, etc, etc 3) I'm thinking about using a browser interface because (a) from what I've read, browser apps can look really great, and (b) I understand there are lots of free tools to assist in setting up the GUI/GUI code with drag and drop tools, so that helps my "keep it simple" goal. 4) I want the program to be totally portable so it runs completely from one single folder on a user's PC. If I do go the browser app router, a major concern I have is the possibility that a user's browser settings could affect or break the app. How likely is this? What other pros and cons are there for my situation?

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