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• Python virtualenv questions

  - by orokusaki

  I'm using VirtualEnv on Windows XP. I'm wondering if I have my brain wrapped around it correctly. I ran virtualenv ENV and it created C:\WINDOWS\system32\ENV. I then changed my PATH variable to include C:\WINDOWS\system32\ENV\Scripts instead of C:\Python27\Scripts. Then, I checked out Django into C:\WINDOWS\system32\ENV\Lib\site-packages\django-trunk, updated my PYTHON_PATH variable to point the new Django directory, and continued to easy_install other things (which of course go into my new C:\WINDOWS\system32\ENV\Lib\site-packages directory). I understand why I should use VirtualEnv so I can run multiple versions of Django, and other libraries on the same machine, but does this mean that to switch between environments I have to basically change my PATH and PYTHON_PATH variable? So, I go from developing one Django project which uses Django 1.2 in an environment called ENV and then change my PATH and such so that I can use an environment called ENV2 which has the dev version of Django? Is that basically it, or is there some better way to automatically do all this (I could update my path in Python code, but that would require me to write machine-specific code in my application)? Also, how does this process compare to using VirtualEnv on Linux (I'm quite the beginner at Linux).

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• how to implement a really efficient bitvector sorting in python

  - by xiao

  Hello guys! Actually this is an interesting topic from programming pearls, sorting 10 digits telephone numbers in a limited memory with an efficient algorithm. You can find the whole story here What I am interested in is just how fast the implementation could be in python. I have done a naive implementation with the module bitvector. The code is as following: from BitVector import BitVector import timeit import random import time import sys def sort(input_li): return sorted(input_li) def vec_sort(input_li): bv = BitVector( size = len(input_li) ) for i in input_li: bv[i] = 1 res_li = [] for i in range(len(bv)): if bv[i]: res_li.append(i) return res_li if __name__ == "__main__": test_data = range(int(sys.argv[1])) print 'test_data size is:', sys.argv[1] random.shuffle(test_data) start = time.time() sort(test_data) elapsed = (time.time() - start) print "sort function takes " + str(elapsed) start = time.time() vec_sort(test_data) elapsed = (time.time() - start) print "sort function takes " + str(elapsed) start = time.time() vec_sort(test_data) elapsed = (time.time() - start) print "vec_sort function takes " + str(elapsed) I have tested from array size 100 to 10,000,000 in my macbook(2GHz Intel Core 2 Duo 2GB SDRAM), the result is as following: test_data size is: 1000 sort function takes 0.000274896621704 vec_sort function takes 0.00383687019348 test_data size is: 10000 sort function takes 0.00380706787109 vec_sort function takes 0.0371489524841 test_data size is: 100000 sort function takes 0.0520560741425 vec_sort function takes 0.374383926392 test_data size is: 1000000 sort function takes 0.867373943329 vec_sort function takes 3.80475401878 test_data size is: 10000000 sort function takes 12.9204008579 vec_sort function takes 38.8053860664 What disappoints me is that even when the test_data size is 100,000,000, the sort function is still faster than vec_sort. Is there any way to accelerate the vec_sort function?

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• Difference in regex between Python and Rubular?

  - by Rosarch

  In Rubular, I have created a regular expression: (Prerequisite|Recommended): (\w|-| )* It matches the bolded: Recommended: good comfort level with computers and some of the arts. Summer. 2 credits. Prerequisite: pre-freshman standing or permission of instructor. Credit may not be applied toward engineering degree. S-U grades only. Here is a use of the regex in Python: note_re = re.compile(r'(Prerequisite|Recommended): (\w|-| )*', re.IGNORECASE) def prereqs_of_note(note): match = note_re.match(note) if not match: return None return match.group(0) Unfortunately, the code returns None instead of a match: >>> import prereqs >>> result = prereqs.prereqs_of_note("Summer. 2 credits. Prerequisite: pre-fres hman standing or permission of instructor. Credit may not be applied toward engi neering degree. S-U grades only.") >>> print result None What am I doing wrong here?

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• Python Multiword Index

  - by Manab Chetia

  index = {'Michael': [['mj.com',1], ['Nine.com',9],['i.com', 34]], / 'Jackson': [['One.com',4],['mj.com', 2],['Nine.com', 10], ['i.com', 45]], / 'Thriller' : [['Seven.com', 7], ['Ten.com',10], ['One.com', 5], ['mj.com',3]} # In this dictionary (index), for eg: 'KEYWORD': # [['THE LINK in which KEYWORD is present,'POSITION # of KEYWORD in the page specified by link']] eg: Michael is present in MJ.com, NINE.com, and i.com at positions 1, 9, 34 of respective pages. Please help me with a python procedure which takes index and KEYWORDS as input. When i enter 'MICHAEL'. The result should be: >>['mj.com', 'nine.com', 'i.com'] When I enter 'MICHAEL JACKSON'. The result should be : >>['mj.com', 'Nine.com'] as 'Michael' and 'Jackson' are present at 'mj.com' and 'nine.com' consecutively i.e. in positions (1,2) & (9,10) respectively. The result should not show 'i.com' even though it contains both KEYWORDS but they are not placed consecutively. When I enter 'MICHAEL JACKSON THRILLER', the result should be ['mj.com'] as the 3 words 'MICHAEL', 'JACKSON', 'THRILLER' are placed consecutively in 'mj.com' ie positions (1, 2, 3) respectively. If I enter 'THRILLER JACKSON' or 'THRILLER FEDERER', the result should be NONE.

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• Python: Most efficient way to concatenate and rearrange files

  - by user300890

  Hi, I am reading from several files, each file is divided into 2 pieces, first a header section of a few thousand lines followed by a body of a few thousand. My problem is I need to concatenate these files into one file where all the headers are on the top followed by the body. Currently I am using two loops; one to pull out all the headers and write them, and the second to write the body of each file (I also include a tmp_count variable to limit the number of lines to be loading into memory before dumping to file). This is pretty slow - about 6min for 13gb file. Can anyone tell me how to optimize this or if there is a faster way to do this in python ? Thanks! Here is my code: def cat_files_sam(final_file_name,work_directory_master,file_count): final_file = open(final_file_name,"w") if len(file_count) > 1: file_count=sort_output_files(file_count) # only for @ headers for bowtie_file in file_count: #print bowtie_file tmp_list = [] tmp_count = 0 for line in open(os.path.join(work_directory_master,bowtie_file)): if line.startswith("@"): if tmp_count == 1000000: final_file.writelines(tmp_list) tmp_list = [] tmp_count = 0 tmp_list.append(line) tmp_count += 1 else: final_file.writelines(tmp_list) break for bowtie_file in file_count: #print bowtie_file tmp_list = [] tmp_count = 0 for line in open(os.path.join(work_directory_master,bowtie_file)): if line.startswith("@"): continue if tmp_count == 1000000: final_file.writelines(tmp_list) tmp_list = [] tmp_count = 0 tmp_list.append(line) tmp_count += 1 final_file.writelines(tmp_list) final_file.close()

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• Querying the Datastore in python

  - by Ray

  Greetings! I am trying to work with a single column in the datatstore, I can view and display the contents, like this - q = test.all() q.filter("adjclose =", "adjclose") q = db.GqlQuery("SELECT * FROM test") results = q.fetch(5) for p in results: p1 = p.adjclose print "The value is --> %f" % (p.adjclose) however i need to calculate the historical values with the adjclose column, and I am not able to get over the errors for c in range(len(p1)-1): TypeError: object of type 'float' has no len() here is my code! for c in range(len(p1)-1): p1.append(p1[c+1]-p1[c]/p1[c]) p2 = (p1[c+1]-p1[c]/p1[c]) print "the p1 value<-- %f" % (p2) print "dfd %f" %(p1) new to python, any help will be greatly appreciated! thanks in advance Ray HERE IS THE COMPLETE CODE class CalHandler(webapp.RequestHandler): def get(self): que = db.GqlQuery("SELECT * from test") user_list = que.fetch(limit=100) doRender( self, 'memberscreen2.htm', {'user_list': user_list} ) q = test.all() q.filter("adjclose =", "adjclose") q = db.GqlQuery("SELECT * FROM test") results = q.fetch(5) for p in results: p1 = p.adjclose print "The value is --> %f" % (p.adjclose) for c in range(len(p1)-1): p1.append(p1[c+1]-p1[c]/p1[c]) print "the p1 value<--> %f" % (p2) print "dfd %f" %(p1)

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• how to multithread on a python server

  - by user3732790

  HELP please i have this code import socket from threading import * import time HOST = '' # Symbolic name meaning all available interfaces PORT = 8888 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) print ('Socket created') s.bind((HOST, PORT)) print ('Socket bind complete') s.listen(10) print ('Socket now listening') def listen(conn): odata = "" end = 'end' while end == 'end': data = conn.recv(1024) if data != odata: odata = data print(data) if data == b'end': end = "" print("conection ended") conn.close() while True: time.sleep(1) conn, addr = s.accept() print ('Connected with ' + addr[0] + ':' + str(addr[1])) Thread.start_new_thread(listen,(conn)) and i would like it so that when ever a person comes onto the server it has its own thread. but i can't get it to work please someone help me. :_( here is the error code: Socket created Socket bind complete Socket now listening Connected with 127.0.0.1:61475 Traceback (most recent call last): File "C:\Users\Myles\Desktop\test recever - Copy.py", line 29, in <module> Thread.start_new_thread(listen,(conn)) AttributeError: type object 'Thread' has no attribute 'start_new_thread' i am on python version 3.4.0 and here is the users code: import socket #for sockets import time s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) print('Socket Created') host = 'localhost' port = 8888 remote_ip = socket.gethostbyname( host ) print('Ip address of ' + host + ' is ' + remote_ip) #Connect to remote server s.connect((remote_ip , port)) print ('Socket Connected to ' + host + ' on ip ' + remote_ip) while True: message = input("> ") #Set the whole string s.send(message.encode('utf-8')) print ('Message send successfully') data = s.recv(1024) print(data) s.close

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• Creating subtree from tree which is represented in xml - python

  - by Jay

  Hi I have an XML (in the form of tree), I require to create sub-tree out of it. For ex: <a> <b> <c>Hello</c> <d> <e>Hi</e> </a> Subtree would be <root> <a> <b> <c>Hello</c> </b> </a> <a> <d> <e>Hi</e> </d> </a> </root> What is the best XML library in python to do it? Any algorithm that already does this would also be helpful. Note: the XML doc won't be that big, it will easily fit in memory.

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• Python optimization problem?

  - by user342079

  Alright, i had this homework recently (don't worry, i've already done it, but in c++) but I got curious how i could do it in python. The problem is about 2 light sources that emit light. I won't get into details tho. Here's the code (that I've managed to optimize a bit in the latter part): import math, array import numpy as np from PIL import Image size = (800,800) width, height = size s1x = width * 1./8 s1y = height * 1./8 s2x = width * 7./8 s2y = height * 7./8 r,g,b = (255,255,255) arr = np.zeros((width,height,3)) hy = math.hypot print 'computing distances (%s by %s)'%size, for i in xrange(width): if i%(width/10)==0: print i, if i%20==0: print '.', for j in xrange(height): d1 = hy(i-s1x,j-s1y) d2 = hy(i-s2x,j-s2y) arr[i][j] = abs(d1-d2) print '' arr2 = np.zeros((width,height,3),dtype="uint8") for ld in [200,116,100,84,68,52,36,20,8,4,2]: print 'now computing image for ld = '+str(ld) arr2 *= 0 arr2 += abs(arr%ld-ld/2)*(r,g,b)/(ld/2) print 'saving image...' ar2img = Image.fromarray(arr2) ar2img.save('ld'+str(ld).rjust(4,'0')+'.png') print 'saved as ld'+str(ld).rjust(4,'0')+'.png' I have managed to optimize most of it, but there's still a huge performance gap in the part with the 2 for-s, and I can't seem to think of a way to bypass that using common array operations... I'm open to suggestions :D

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• Python and the self parameter

  - by Svend

  I'm having some issues with the self parameter, and some seemingly inconsistent behavior in Python is annoying me, so I figure I better ask some people in the know. I have a class, Foo. This class will have a bunch of methods, m1, through mN. For some of these, I will use a standard definition, like in the case of m1 below. But for others, it's more convinient to just assign the method name directly, like I've done with m2 and m3. import os def myfun(x, y): return x + y class Foo(): def m1(self, y, z): return y + z + 42 m2 = os.access m3 = myfun f = Foo() print f.m1(1, 2) print f.m2("/", os.R_OK) print f.m3(3, 4) Now, I know that os.access does not take a self parameter (seemingly). And it still has no issues with this type of assignment. However, I cannot do the same for my own modules (imagine myfun defined off in mymodule.myfun). Running the above code yields the following output: 3 True Traceback (most recent call last): File "foo.py", line 16, in <module> print f.m3(3, 4) TypeError: myfun() takes exactly 2 arguments (3 given) The problem is that, due to the framework I work in, I cannot avoid having a class Foo at least. But I'd like to avoid having my mymodule stuff in a dummy class. In order to do this, I need to do something ala def m3(self,a1, a2): return mymodule.myfun(a1,a2) Which is hugely redundant when you have like 20 of them. So, the question is, either how do I do this in a totally different and obviously much smarter way, or how can I make my own modules behave like the built-in ones, so it does not complain about receiving 1 argument too many.

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• Validating and filling default values in XML based on XSD in Python

  - by PoltoS

  I have an XML like <a> <b/> <b c="2"/> </a> I have my XSD <xs:element name="a"> <xs:complexType> <xs:sequence> <xs:element name="b" maxOccurs="unbounded"> <xs:attribute name="c" default="1"/> </xs:element> </xs:sequence> </xs:complexType> </xs:element> I want to use my XSD to validate my original XML and fill all default values: <a> <b c="1"/> <b c="2"/> </a> How do I get it in Python? With validation there is no problem (e.g. XMLSchema). The problem are the default values.

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• Python: two loops at once

  - by Stephan Meijer

  I've got a problem: I am new to Python and I want to do multiple loops. I want to run a WebSocket client (Autobahn) and I want to run a loop which shows the filed which are edited in a specific folder (pyinotify or else Watchdog). Both are running forever, Great. Is there a way to run them at once and send a message via the WebSocket connection while I'm running the FileSystemWatcher, like with callbacks, multithreading, multiprocessing or just separate files? factory = WebSocketClientFactory("ws://localhost:8888/ws", debug=False) factory.protocol = self.webSocket connectWS(factory) reactor.run() If we run this, it will have success. But if we run this: factory = WebSocketClientFactory("ws://localhost:8888/ws", debug=False) factory.protocol = self.webSocket connectWS(factory) reactor.run() # Websocket client running now,running the filewatcher wm = pyinotify.WatchManager() mask = pyinotify.IN_DELETE | pyinotify.IN_CREATE # watched events class EventHandler(pyinotify.ProcessEvent): def process_IN_CREATE(self, event): print "Creating:", event.pathname def process_IN_DELETE(self, event): print "Removing:", event.pathname handler = EventHandler() notifier = pyinotify.Notifier(wm, handler) wdd = wm.add_watch('/tmp', mask, rec=True) notifier.loop() This will create 2 loops, but since we already have a loop, the code after 'reactor.run()' will not run at all.. For your information: this project is going to be a sync client. Thanks a lot!

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• python gui generate math equation

  - by Nero Dietrich

  I have a homework question for one specific item with python GUIs. My goal is to create a GUI that asks a random mathematical equation and if the equation is evaluated correctly, then I will receive a message stating that it is correct. My main problem is finding out where to place my statements so that they show up in the labels; I have 1 textbox which generates the random equation, the next textbox is blank for me to enter the solution, and then an "Enter" button at the end to evaluate my solution. It looks like this: [randomly generated equation][Empty space to enter solution] [ENTER] I've managed to get the layout and the evaluate parameters, but I don't know where to go from here. This is my code so far: class Equation(Frame): def __init__(self,parent=None): Frame.__init__(self, parent) self.pack() Equation.make_widgets(self) Equation.new_problem(self) def make_widgets(self): Label(self).grid(row=0, column=1) ent = Entry(self) ent.grid(row=0, column=1) Label(self).grid(row=0, column=2) ent = Entry(self) ent.grid(row=0, column=2) Button(self, text='Enter', command=self.evaluate).grid(row=0, column=3) def new_problem(self): pass def evaluate(self): result = eval(self.get()) self.delete(0, END) self.insert(END, result) print('Correct')

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• Python: Copying files with special characters in path

  - by erikderwikinger

  Hi is there any possibility in Python 2.5 to copy files having special chars (Japanese chars, cyrillic letters) in their path? shutil.copy cannot handle this. here is some example code: import copy, os,shutil,sys fname=os.getenv("USERPROFILE")+"\\Desktop\\testfile.txt" print fname print "type of fname: "+str(type(fname)) fname0 = unicode(fname,'mbcs') print fname0 print "type of fname0: "+str(type(fname0)) fname1 = unicodedata.normalize('NFKD', fname0).encode('cp1251','replace') print fname1 print "type of fname1: "+str(type(fname1)) fname2 = unicode(fname,'mbcs').encode(sys.stdout.encoding) print fname2 print "type of fname2: "+str(type(fname2)) shutil.copy(fname2,'C:\\') the output on a Russian Windows XP C:\Documents and Settings\+????????????\Desktop\testfile.txt type of fname: <type 'str'> C:\Documents and Settings\?????????????\Desktop\testfile.txt type of fname0: <type 'unicode'> C:\Documents and Settings\+????????????\Desktop\testfile.txt type of fname1: <type 'str'> C:\Documents and Settings\?????????????\Desktop\testfile.txt type of fname2: <type 'str'> Traceback (most recent call last): File "C:\Test\getuserdir.py", line 23, in <module> shutil.copy(fname2,'C:\\') File "C:\Python25\lib\shutil.py", line 80, in copy copyfile(src, dst) File "C:\Python25\lib\shutil.py", line 46, in copyfile fsrc = open(src, 'rb') IOError: [Errno 2] No such file or directory: 'C:\\Documents and Settings\\\x80\ xa4\xac\xa8\xad\xa8\xe1\xe2\xe0\xa0\xe2\xae\xe0\\Desktop\\testfile.txt'

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• linear combinations in python/numpy

  - by nmaxwell

  greetings, I'm not sure if this is a dumb question or not. Lets say I have 3 numpy arrays, A1,A2,A3, and 3 floats, c1,c2,c3 and I'd like to evaluate B = A1*c1+ A2*c2+ A3*c3 will numpy compute this as for example, E1 = A1*c1 E2 = A2*c2 E3 = A3*c3 D1 = E1+E2 B = D1+E3 or is it more clever than that? In c++ I had a neat way to abstract this kind of operation. I defined series of general 'LC' template functions, LC for linear combination like: template<class T,class D> void LC( T & R, T & L0,D C0, T & L1,D C1, T & L2,D C2) { R = L0*C0 +L1*C1 +L2*C2; } and then specialized this for various types, so for instance, for an array the code looked like for (int i=0; i<L0.length; i++) R.array[i] = L0.array[i]*C0 + L1.array[i]*C1 + L2.array[i]*C2; thus avoiding having to create new intermediate arrays. This may look messy but it worked really well. I could do something similar in python, but I'm not sure if its nescesary. Thanks in advance for any insight. -nick

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• Parse a CSV file using python (to make a decision tree later)

  - by Margaret

  First off, full disclosure: This is going towards a uni assignment, so I don't want to receive code. :). I'm more looking for approaches; I'm very new to python, having read a book but not yet written any code. The entire task is to import the contents of a CSV file, create a decision tree from the contents of the CSV file (using the ID3 algorithm), and then parse a second CSV file to run against the tree. There's a big (understandable) preference to have it capable of dealing with different CSV files (I asked if we were allowed to hard code the column names, mostly to eliminate it as a possibility, and the answer was no). The CSV files are in a fairly standard format; the header row is marked with a # then the column names are displayed, and every row after that is a simple series of values. Example: # Column1, Column2, Column3, Column4 Value01, Value02, Value03, Value04 Value11, Value12, Value13, Value14 At the moment, I'm trying to work out the first part: parsing the CSV. To make the decisions for the decision tree, a dictionary structure seems like it's going to be the most logical; so I was thinking of doing something along these lines: Read in each line, character by character If the character is not a comma or a space Append character to temporary string If the character is a comma Append the temporary string to a list Empty string Once a line has been read Create a dictionary using the header row as the key (somehow!) Append that dictionary to a list However, if I do things that way, I'm not sure how to make a mapping between the keys and the values. I'm also wondering whether there is some way to perform an action on every dictionary in a list, since I'll need to be doing things to the effect of "Everyone return their values for columns Column1 and Column4, so I can count up who has what!" - I assume that there is some mechanism, but I don't think I know how to do it. Is a dictionary the best way to do it? Would I be better off doing things using some other data structure? If so, what?

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• Sending buffered images between Java client and Twisted Python socket server

  - by PattimusPrime

  I have a server-side function that draws an image with the Python Imaging Library. The Java client requests an image, which is returned via socket and converted to a BufferedImage. I prefix the data with the size of the image to be sent, followed by a CR. I then read this number of bytes from the socket input stream and attempt to use ImageIO to convert to a BufferedImage. In abbreviated code for the client: public String writeAndReadSocket(String request) { // Write text to the socket BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())); bufferedWriter.write(request); bufferedWriter.flush(); // Read text from the socket BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream())); // Read the prefixed size int size = Integer.parseInt(bufferedReader.readLine()); // Get that many bytes from the stream char[] buf = new char[size]; bufferedReader.read(buf, 0, size); return new String(buf); } public BufferedImage stringToBufferedImage(String imageBytes) { return ImageIO.read(new ByteArrayInputStream(s.getBytes())); } and the server: # Twisted server code here # The analog of the following method is called with the proper client # request and the result is written to the socket. def worker_thread(): img = draw_function() buf = StringIO.StringIO() img.save(buf, format="PNG") img_string = buf.getvalue() return "%i\r%s" % (sys.getsizeof(img_string), img_string) This works for sending and receiving Strings, but image conversion (usually) fails. I'm trying to understand why the images are not being read properly. My best guess is that the client is not reading the proper number of bytes, but I honestly don't know why that would be the case. Side notes: I realize that the char[]-to-String-to-bytes-to-BufferedImage Java logic is roundabout, but reading the bytestream directly produces the same errors. I have a version of this working where the client socket isn't persistent, ie. the request is processed and the connection is dropped. That version works fine, as I don't need to care about the image size, but I want to learn why the proposed approach doesn't work.

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• Python FTP grabbing and saving images issue

  - by PylonsN00b

  OK So I have been messing with this all day long. I am fairly new to Python FTP. So I have searched through here and came up w/ this: images = notions_ftp.nlst() for image_name in image_names: if found_url == False: try: for image in images: ftp_image_name = "./%s" % image_name if ftp_image_name == image: found_url = True image_name_we_want = image_name except: pass # We failed to find an image for this product, it will have to be done manually if found_url == False: log.info("Image ain't there baby -- SKU: %s" % sku) return False # Hey we found something! Open the image.... notions_ftp.retrlines("RETR %s" % image_name_we_want, open(image_name_we_want, "rb")) 1/0 So I have narrowed the error down to the line before I divide by zero. Here is the error: Traceback (most recent call last): File "<console>", line 6, in <module> File "<console>", line 39, in insert_image IOError: [Errno 2] No such file or directory: '411483CC-IT,IM.jpg' So if you follow the code you will see that the image IS in the directory because image_name_we_want is set if found in that directory listing on the first line of my code. And I KNOW it's there because I am looking at the FTP site myself and ...it's freakin there. So at some point during all of this I got the image to save locally, which is most desired, but I have long since forgot what I used to make it do that. Either way, why does it think that the image isn't there when it clearly finds it in the listing.

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• Python Multiprocessing Question

  - by Avan

  My program has 2 parts divided into the core and downloader. The core handles all the app logic while the downloader just downloads urls. Right now, I am trying to use the python multiprocessing module to accomplish the task of the core as a process and the downloader as a process. The first problem I noticed was that if I spawn the downloader process from the core process so that the downloader is the child process and the core is the parent, the core process(parent) is blocked until the child is finished. I do not want this behaivor though. I would like to have a core process and a downloader process that are both able to execute their code and communicate between each other. example ... def main(): jobQueue = Queue() jobQueue.put("http://google.com) d = Downloader(jobQueue) p = Process(target=d.start()) p.start() if __name__ == '__main__': freeze_support() main() where Downloader's start() just takes the url out of the queue and downloads it. In order to have the 2 processes unblocked, would I need to create 2 processes from the parent process and then share something between them?

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• Python: Serial Transmission

  - by Silent Elektron

  I have an image stack of 500 images (jpeg) of 640x480. I intend to make 500 pixels (1st pixels of all images) as a list and then send that via COM1 to FPGA where I do my further processing. I have a couple of questions here: How do I import all the 500 images at a time into python and how do i store it? How do I send the 500 pixel list via COM1 to FPGA? I tried the following: Converted the jpeg image to intensity values (each pixel is denoted by a number between 0 and 255) in MATLAB, saved the intensity values in a text file, read that file using readlines(). But it became too cumbersome to make the intensity value files for all the 500 images! Used NumPy to put the read files in a matrix and then pick the first pixel of all images. But when I send it, its coming like: [56, 61, 78, ... ,71, 91]. Is there a way to eliminate the [ ] and , while sending the data serially? Thanks in Advance! :)

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• Python: Errors saving and loading objects with pickle module

  - by Peterstone

  Hi, I am trying to load and save objects with this piece of code I get it from a question I asked a week ago: Python: saving and loading objects and using pickle. The piece of code is this: class Fruits: pass banana = Fruits() banana.color = 'yellow' banana.value = 30 import pickle filehandler = open("Fruits.obj","wb") pickle.dump(banana,filehandler) filehandler.close() file = open("Fruits.obj",'rb') object_file = pickle.load(file) file.close() print(object_file.color, object_file.value, sep=', ') At a first glance the piece of code works well, getting load and see the 'color' and 'value' of the saved object. But, what I pursuit is to close a session, open a new one and load what I save in a past session. I close the session after putting the line filehandler.close() and I open a new one and I put the rest of your code, then after putting object_file = pickle.load(file) I get this error: Traceback (most recent call last): File "<pyshell#5>", line 1, in <module> object_file = pickle.load(file) File "C:\Python31\lib\pickle.py", line 1365, in load encoding=encoding, errors=errors).load() AttributeError: 'module' object has no attribute 'Fruits' Can anyone explain me what this error message means and telling me how to solve this problem? Thank so much and happy new year!!

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• Calculating a total cost in Python

  - by Sérgio Lourenço

  I'm trying to create a trip planner in python, but after I defined all the functions I'm not able to call and calculate them in the last function tripCost(). In tripCost, I want to put the days and travel destination (city) and the program runs the functions and gives me the exact result of all the 3 functions previously defined. Code: def hotelCost(): days = raw_input ("How many nights will you stay at the hotel?") total = 140 * int(days) print "The total cost is",total,"dollars" def planeRideCost(): city = raw_input ("Wich city will you travel to\n") if city == 'Charlotte': return "The cost is 183$" elif city == 'Tampa': return "The cost is 220$" elif city == 'Pittsburgh': return "The cost is 222$" elif city == 'Los Angeles': return "The cost is 475$" else: return "That's not a valid destination" def rentalCarCost(): rental_days = raw_input ("How many days will you rent the car\n") discount_3 = 40 * int(rental_days) * 0.2 discount_7 = 40 * int(rental_days) * 0.5 total_rent3 = 40 * int(rental_days) - discount_3 total_rent7 = 40 * int(rental_days) - discount_7 cost_day = 40 * int(rental_days) if int(rental_days) >= 3: print "The total cost is", total_rent3, "dollars" elif int(rental_days) >= 7: print "The total cost is", total_rent7, "dollars" else: print "The total cost is", cost_day, "dollars" def tripCost(): travel_city = raw_input ("What's our destination\n") days_travel = raw_input ("\nHow many days will you stay\n") total_trip_cost = hotelCost(int(day_travel)) + planeRideCost (str(travel_city)) + rentalCost (int(days_travel)) return "The total cost with the trip is", total_trip_cost tripCost()

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• How do I override a python import?

  - by Evan Plaice

  So I'm working on pypreprocessor which is a preprocessor that takes c-style directives and I've been able to make it work like a traditional preprocessor (it's self-consuming and executes postprocessed code on-the-fly) except that it breaks library imports. The problem is. The preprocessor runs through the file, processes' it, outputs to a temp file, and exec() the temp file. Libraries that are imported need to be handled a little different because they aren't executed but rather loaded and made accessible to the caller module. What I need to be able to do is. Interrupt the import (since the preprocessor is being run in the middle of the import), load the postprocessed code as a tempModule, and replace the original import with the tempModule to trick the calling script with the import into believing that the tempModule is the original module. I have searched everywhere and so far, have no solution. This question is the closest I've seen so far to providing an answer: http://stackoverflow.com/questions/1096216/override-namespace-in-python Here's what I have. # remove the bytecode file created by the first import os.remove(moduleName + '.pyc') # remove the first import del sys.modules[moduleName] # import the postprocessed module tmpModule = __import__(tmpModuleName) # set first module's reference to point to the preprocessed module sys.modules[moduleName] = tmpModule moduleName is the name of the original module, tmpModuleName is the name of the postprocessed code file. The strange part is, this solution still runs completely normal as if the first module completed loaded normally; unless you remove the last line, then you get a module not found error. Hopefully someone on SO know a lot more about imports than I do because this one has me stumped.

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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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