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• What is the easiest way to read wav-files using Python [summary]?

  - by Roman

  I want to use Python to access a wav-file and write its content in a form which allows me to analyze it (let's say arrays). I heard that "audiolab" is a suitable tool for that (it transforms numpy arrays into wav and vica versa). I have installed the "audiolab" but I had a problem with the version of numpy (I could not "from numpy.testing import Tester"). I had 1.1.1. version of numpy. I have installed a newer version on numpy (1.4.0). But then I got a new set of errors: Traceback (most recent call last): File "test.py", line 7, in import scikits.audiolab File "/usr/lib/python2.5/site-packages/scikits/audiolab/init.py", line 25, in from pysndfile import formatinfo, sndfile File "/usr/lib/python2.5/site-packages/scikits/audiolab/pysndfile/init.py", line 1, in from _sndfile import Sndfile, Format, available_file_formats, available_encodings File "numpy.pxd", line 30, in scikits.audiolab.pysndfile._sndfile (scikits/audiolab/pysndfile/_sndfile.c:9632) ValueError: numpy.dtype does not appear to be the correct type object I gave up to use audiolab and thought that I can use "wave" package to read in a wav-file. I asked a question about that but people recommended to use scipy instead. OK, I decided to focus on scipy (I have 0.6.0. version). But when I tried to do the following: from scipy.io import wavfile x = wavfile.read('/usr/share/sounds/purple/receive.wav') I get the following: Traceback (most recent call last): File "test3.py", line 4, in <module> from scipy.io import wavfile File "/usr/lib/python2.5/site-packages/scipy/io/__init__.py", line 23, in <module> from numpy.testing import NumpyTest ImportError: cannot import name NumpyTest So, I gave up to use scipy. Can I use just wave package? I do not need much. I just need to have content of wav-file in human readable format and than I will figure out what to do with that.

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• Python's asyncore to periodically send data using a variable timeout. Is there a better way?

  - by Nick Sonneveld

  I wanted to write a server that a client could connect to and receive periodic updates without having to poll. The problem I have experienced with asyncore is that if you do not return true when dispatcher.writable() is called, you have to wait until after the asyncore.loop has timed out (default is 30s). The two ways I have tried to work around this is 1) reduce timeout to a low value or 2) query connections for when they will next update and generate an adequate timeout value. However if you refer to 'Select Law' in 'man 2 select_tut', it states, "You should always try to use select() without a timeout." Is there a better way to do this? Twisted maybe? I wanted to try and avoid extra threads. I'll include the variable timeout example here: #!/usr/bin/python import time import socket import asyncore # in seconds UPDATE_PERIOD = 4.0 class Channel(asyncore.dispatcher): def __init__(self, sock, sck_map): asyncore.dispatcher.__init__(self, sock=sock, map=sck_map) self.last_update = 0.0 # should update immediately self.send_buf = '' self.recv_buf = '' def writable(self): return len(self.send_buf) > 0 def handle_write(self): nbytes = self.send(self.send_buf) self.send_buf = self.send_buf[nbytes:] def handle_read(self): print 'read' print 'recv:', self.recv(4096) def handle_close(self): print 'close' self.close() # added for variable timeout def update(self): if time.time() >= self.next_update(): self.send_buf += 'hello %f\n'%(time.time()) self.last_update = time.time() def next_update(self): return self.last_update + UPDATE_PERIOD class Server(asyncore.dispatcher): def __init__(self, port, sck_map): asyncore.dispatcher.__init__(self, map=sck_map) self.port = port self.sck_map = sck_map self.create_socket(socket.AF_INET, socket.SOCK_STREAM) self.bind( ("", port)) self.listen(16) print "listening on port", self.port def handle_accept(self): (conn, addr) = self.accept() Channel(sock=conn, sck_map=self.sck_map) # added for variable timeout def update(self): pass def next_update(self): return None sck_map = {} server = Server(9090, sck_map) while True: next_update = time.time() + 30.0 for c in sck_map.values(): c.update() # <-- fill write buffers n = c.next_update() #print 'n:',n if n is not None: next_update = min(next_update, n) _timeout = max(0.1, next_update - time.time()) asyncore.loop(timeout=_timeout, count=1, map=sck_map)

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• How to compare 2 lists and merge them in Python/MySQL?

  - by NJTechGuy

  I want to merge data. Following are my MySQL tables. I want to use Python to traverse though a list of both Lists (one with dupe = 'x' and other with null dupes). For instance : a b c d e f key dupe -------------------- 1 d c f k l 1 x 2 g h j 1 3 i h u u 2 4 u r t 2 x From the above sample table, the desired output is : a b c d e f key dupe -------------------- 2 g c h k j 1 3 i r h u u 2 What I have so far : import string, os, sys import MySQLdb from EncryptedFile import EncryptedFile enc = EncryptedFile( os.getenv("HOME") + '/.py-encrypted-file') user = enc.getValue("user") pw = enc.getValue("pw") db = MySQLdb.connect(host="127.0.0.1", user=user, passwd=pw,db=user) cursor = db.cursor() cursor2 = db.cursor() cursor.execute("select * from delThisTable where dupe is null") cursor2.execute("select * from delThisTable where dupe is not null") result = cursor.fetchall() result2 = cursor2.fetchall() for cursorFieldname in cursor.description: for cursorFieldname2 in cursor2.description: if cursorFieldname[0] == cursorFieldname2[0]: ### How do I compare the record with same key value and update the original row null field value with the non-null value from the duplicate? Please fill this void... cursor.close() cursor2.close() db.close() Thanks guys!

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• Why can't I pass self as a named argument to an instance method in Python?

  - by Joseph Garvin

  This works: >>> def bar(x, y): ... print x, y ... >>> bar(y=3, x=1) 1 3 And this works: >>> class foo(object): ... def bar(self, x, y): ... print x, y ... >>> z = foo() >>> z.bar(y=3, x=1) 1 3 And even this works: >>> foo.bar(z, y=3, x=1) 1 3 But why doesn't this work? >>> foo.bar(self=z, y=3, x=1) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unbound method bar() must be called with foo instance as first argument (got nothing instead) This makes metaprogramming more difficult, because it requires special case handling. I'm curious if it's somehow necessary by Python's semantics or just an artifact of implementation.

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• django + south + python: strange behavior when using a text string received as a parameter in a func

  - by carlosescri

  Hello, this is my first question. I'm trying to execute a SQL query in django (south migration): from django.db import connection # ... class Migration(SchemaMigration): # ... def transform_id_to_pk(self, table): try: db.delete_primary_key(table) except: pass finally: cursor = connection.cursor() # This does not work cursor.execute('SELECT MAX("id") FROM "%s"', [table]) # I don't know if this works. try: minvalue = cursor.fetchone()[0] except: minvalue = 1 seq_name = table + '_id_seq' db.execute('CREATE SEQUENCE "%s" START WITH %s OWNED BY "%s"."id"', [seq_name, minvalue, table]) db.execute('ALTER TABLE "%s" ALTER COLUMN id SET DEFAULT nextval("%s")', [table, seq_name + '::regclass']) db.create_primary_key(table, ['id']) # ... I use this function like this: self.transform_id_to_pk('my_table_name') So it should: Find the biggest existent ID or 0 (it crashes) Create a sequence name Create the sequence Update the ID field to use sequence Update the ID as PK But it crashes and the error says: File "../apps/accounting/migrations/0003_setup_tables.py", line 45, in forwards self.delegation_table_setup(orm) File "../apps/accounting/migrations/0003_setup_tables.py", line 478, in delegation_table_setup self.transform_id_to_pk('accounting_delegation') File "../apps/accounting/migrations/0003_setup_tables.py", line 20, in transform_id_to_pk cursor.execute(u'SELECT MAX("id") FROM "%s"', [table.encode('utf-8')]) File "/Library/Python/2.6/site-packages/django/db/backends/util.py", line 19, in execute return self.cursor.execute(sql, params) psycopg2.ProgrammingError: relation "E'accounting_delegation'" does not exist LINE 1: SELECT MAX("id") FROM "E'accounting_delegation'" ^ I have shortened the file paths for convenience. What does that "E'accounting_delegation'" mean? How could I get rid of it? Thank you! Carlos.

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• How can you get the call tree with python profilers?

  - by Oliver

  I used to use a nice Apple profiler that is built into the System Monitor application. As long as your C++ code was compiled with debug information, you could sample your running application and it would print out an indented tree telling you what percent of the parent function's time was spent in this function (and the body vs. other function calls). For instance, if main called function_1 and function_2, function_2 calls function_3, and then main calls function_3: main (100%, 1% in function body): function_1 (9%, 9% in function body): function_2 (90%, 85% in function body): function_3 (100%, 100% in function body) function_3 (1%, 1% in function body) I would see this and think, "Something is taking a long time in the code in the body of function_2. If I want my program to be faster, that's where I should start." Does anyone know how I can most easily get this exact profiling output for a python program? I've seen people say to do this: import cProfile, pstats prof = cProfile.Profile() prof = prof.runctx("real_main(argv)", globals(), locals()) stats = pstats.Stats(prof) stats.sort_stats("time") # Or cumulative stats.print_stats(80) # 80 = how many to print but it's quite messy compared to that elegant call tree. Please let me know if you can easily do this, it would help quite a bit. Cheers!

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• Achieving Thread-Safety

  - by Smasher

  Question How can I make sure my application is thread-safe? Are their any common practices, testing methods, things to avoid, things to look for? Background I'm currently developing a server application that performs a number of background tasks in different threads and communicates with clients using Indy (using another bunch of automatically generated threads for the communication). Since the application should be highly availabe, a program crash is a very bad thing and I want to make sure that the application is thread-safe. No matter what, from time to time I discover a piece of code that throws an exception that never occured before and in most cases I realize that it is some kind of synchronization bug, where I forgot to synchronize my objects properly. Hence my question concerning best practices, testing of thread-safety and things like that. mghie: Thanks for the answer! I should perhaps be a little bit more precise. Just to be clear, I know about the principles of multithreading, I use synchronization (monitors) throughout my program and I know how to differentiate threading problems from other implementation problems. But nevertheless, I keep forgetting to add proper synchronization from time to time. Just to give an example, I used the RTL sort function in my code. Looked something like FKeyList.Sort (CompareKeysFunc); Turns out, that I had to synchronize FKeyList while sorting. It just don't came to my mind when initially writing that simple line of code. It's these thins I wanna talk about. What are the places where one easily forgets to add synchronization code? How do YOU make sure that you added sync code in all important places?

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• How do I search & replace all occurrences of a string in a ms word doc with python?

  - by Mark

  Hello there, I am pretty stumped at the moment. Based on http://stackoverflow.com/questions/1045628/can-i-use-win32-com-to-replace-text-inside-a-word-document I was able to code a simple template system that generates word docs out of a template word doc (in Python). My problem is that text in "Text Fields" is not find that way. Even in Word itself there is no option to search everything - you actually have to choose between "Main Document" and "Text Fields". Being new to the Windows world I tried to browse the VBA docs for it but found no help (probably due to "text field" being a very common term). word.Documents.Open(f) wdFindContinue = 1 wdReplaceAll = 2 find_str = '\{\{(*)\}\}' find = word.Selection.Find find.Execute(find_str, False, False, True, False, False, \ True, wdFindContinue, False, False, False) while find.Found: t = word.Selection.Text.__str__() r = process_placeholder(t, answer_data, question_data) if type(r) == dict: errors.append(r) else: find.Execute(t, False, True, False, False, False, \ True, False, False, r, wdReplaceAll) This is the relevant portion of my code. I was able to get around all problems by myself by now (hint: if you want to replace strings with more than 256 chars, you have to do it via clipboard, etc ...) Hope, someone can help me.

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• Python modules not updating after restarting the main module.

  - by Ian

  I've recently come back to a project having had to stop for about 6 months, and after reinstalling my operating system and coming back to it I'm having all kinds of crazy things happen. I made sure to install the same version(2.6) of python that I was using before. It started by giving me strange tkinter error that I hadn't had trouble with before, the program is relatively simple and the 2 or 3 bugs that were left when i quit, I had documented and weren't related to the interface. Things got even weirder when the same error would pop up even after I had removed the offending section of code. In fact, the traceback pointed to a line that didn't even exist in the module it was referencing, eg: line 262 when the module was only 200 lines long. After just starting a completely new file for the main module and copy/pasting it finally recognized that the offending code was gone and I stopped getting the error only to find that any updates to the code I made in another module didn't show up when I restarted the program through the shell. (I didn't forget to save.) After fiddling with this, of course, the old interface error came back, only in a different section of code that had been working previously. In fact, if I revert back to the files I had six months ago, the program works fine. As soon as I change anything in the main module, however, the interface bug comes back. Here's the original error: Exception in Tkinter callback Traceback (most recent call last): File "C:\Python26\lib\lib-tk\Tkinter.py", line 1410, in __call__ return self.func(*args) File "C:\PyStuff\interface.py", line 202, in dispOne __main__.top.destroy() File "C:\Python26\lib\lib-tk\Tkinter.py", line 1938, in destroy self.tk.call('destroy', self._w) TclError: can't invoke "destroy" command: application has been destroyed I'm guessing something else is going on here other than my own poor programming. Anyone have any ideas?

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• Handling user interface in a multi-threaded application (or being forced to have a UI-only main thre

  - by Patrick

  In my application, I have a 'logging' window, which shows all the logging, warnings, errors of the application. Last year my application was still single-threaded so this worked [quite] good. Now I am introducing multithreading. I quickly noticed that it's not a good idea to update the logging window from different threads. Reading some articles on keeping the UI in the main thread, I made a communication buffer, in which the other threads are adding their logging messages, and from which the main thread takes the messages and shows them in the logging window (this is done in the message loop). Now, in a part of my application, the memory usage increases dramatically, because the separate threads are generating lots of logging messages, and the main thread cannot empty the communication buffer quickly enough. After the while the memory decreases again (if the other threads have finished their work and the main thread gradually empties the communication buffer). I solved this problem by having a maximum size on the communication buffer, but then I run into a problem in the following situation: the main thread has to perform a complex action the main thread takes some parts of the action and let's separate threads execute this while the seperate threads are executing their logic, the main thread processes the results from the other threads and continues with its work if the other threads are finished Problem is that in this situation, if the other threads perform logging, there is no UI-message loop, and so the communication buffer is filled, but not emptied. I see two solutions in solving this problem: require the main thread to do regular polling of the communication buffer only performing user interface logic in the main thread (no other logic) I think the second solution seems the best, but this may not that easy to introduce in a big application (in my case it performs mathematical simulations). Are there any other solutions or tips? Or is one of the two proposed the best, easiest, most-pragmatic solution? Thanks, Patrick

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• What about race condition in multithreaded reading?

  - by themoob

  Hi, According to an article on IBM.com, "a race condition is a situation in which two or more threads or processes are reading or writing some shared data, and the final result depends on the timing of how the threads are scheduled. Race conditions can lead to unpredictable results and subtle program bugs." . Although the article concerns Java, I have in general been taught the same definition. As far as I know, simple operation of reading from RAM is composed of setting the states of specific input lines (address, read etc.) and reading the states of output lines. This is an operation that obviously cannot be executed simultaneously by two devices and has to be serialized. Now let's suppose we have a situation when a couple of threads access an object in memory. In theory, this access should be serialized in order to prevent race conditions. But e.g. the readers/writers algorithm assumes that an arbitrary number of readers can use the shared memory at the same time. So, the question is: does one have to implement an exclusive lock for read when using multithreading (in WinAPI e.g.)? If not, why? Where is this control implemented - OS, hardware? Best regards, Kuba

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• Why is my simple python gtk+cairo program running so slowly/stutteringly?

  - by synapz

  My program draws circles moving on the window. I think I must be missing some basic gtk/cairo concept because it seems to be running too slowly/stutteringly for what I am doing. Any ideas? Thanks for any help! #!/usr/bin/python import gtk import gtk.gdk as gdk import math import random import gobject # The number of circles and the window size. num = 128 size = 512 # Initialize circle coordinates and velocities. x = [] y = [] xv = [] yv = [] for i in range(num): x.append(random.randint(0, size)) y.append(random.randint(0, size)) xv.append(random.randint(-4, 4)) yv.append(random.randint(-4, 4)) # Draw the circles and update their positions. def expose(*args): cr = darea.window.cairo_create() cr.set_line_width(4) for i in range(num): cr.set_source_rgb(1, 0, 0) cr.arc(x[i], y[i], 8, 0, 2 * math.pi) cr.stroke_preserve() cr.set_source_rgb(1, 1, 1) cr.fill() x[i] += xv[i] y[i] += yv[i] if x[i] > size or x[i] < 0: xv[i] = -xv[i] if y[i] > size or y[i] < 0: yv[i] = -yv[i] # Self-evident? def timeout(): darea.queue_draw() return True # Initialize the window. window = gtk.Window() window.resize(size, size) window.connect("destroy", gtk.main_quit) darea = gtk.DrawingArea() darea.connect("expose-event", expose) window.add(darea) window.show_all() # Self-evident? gobject.idle_add(timeout) gtk.main()

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• Python: Does one of these examples waste more memory?

  - by orokusaki

  In a Django view function which uses manual transaction committing, I have: context = RequestContext(request, data) transaction.commit() return render_to_response('basic.html', data, context) # Returns a Django ``HttpResponse`` object which is similar to a dictionary. I think it is a better idea to do this: context = RequestContext(request, data) response = render_to_response('basic.html', data, context) transaction.commit() return response If the page isn't rendered correctly in the second version, the transaction is rolled back. This seems like the logical way of doing it albeit there won't likely be many exceptions at that point in the function when the application is in production. But... I fear that this might cost more and this will be replete through a number of functions since the application is heavy with custom transaction handling, so now is the time to figure out. If the HttpResponse instance is in memory already (at the point of render_to_response()), then what does another reference cost? When the function ends, doesn't the reference (response variable) go away so that when Django is done converting the HttpResponse into a string for output Python can immediately garbage collect it? Is there any reason I would want to use the first version (other than "It's 1 less line of code.")?

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• How do I structure my tests with Python unittest module?

  - by persepolis

  I'm trying to build a test framework for automated webtesting in selenium and unittest, and I want to structure my tests into distinct scripts. So I've organised it as following: base.py - This will contain, for now, the base selenium test case class for setting up a session. import unittest from selenium import webdriver # Base Selenium Test class from which all test cases inherit. class BaseSeleniumTest(unittest.TestCase): def setUp(self): self.browser = webdriver.Firefox() def tearDown(self): self.browser.close() main.py - I want this to be the overall test suite from which all the individual tests are run. import unittest import test_example if __name__ == "__main__": SeTestSuite = test_example.TitleSpelling() unittest.TextTestRunner(verbosity=2).run(SeTestSuite) test_example.py - An example test case, it might be nice to make these run on their own too. from base import BaseSeleniumTest # Test the spelling of the title class TitleSpelling(BaseSeleniumTest): def test_a(self): self.assertTrue(False) def test_b(self): self.assertTrue(True) The problem is that when I run main.py I get the following error: Traceback (most recent call last): File "H:\Python\testframework\main.py", line 5, in <module> SeTestSuite = test_example.TitleSpelling() File "C:\Python27\lib\unittest\case.py", line 191, in __init__ (self.__class__, methodName)) ValueError: no such test method in <class 'test_example.TitleSpelling'>: runTest I suspect this is due to the very special way in which unittest runs and I must have missed a trick on how the docs expect me to structure my tests. Any pointers?

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• I don't like Python functions that take two or more iterables. Is it a good idea?

  - by Xavier Ho

  This question came from looking at this question on Stackoverflow. def fringe8((px, py), (x1, y1, x2, y2)): Personally, it's been one of my pet peeves to see a function that takes two arguments with fixed-number iterables (like a tuple) or two or more dictionaries (Like in the Shotgun API). It's just hard to use, because of all the verbosity and double-bracketed enclosures. Wouldn't this be better: >>> class Point(object): ... def __init__(self, x, y): ... self.x = x ... self.y = y ... >>> class Rect(object): ... def __init__(self, x1, y1, x2, y2): ... self.x1 = x1 ... self.y1 = y1 ... self.x2 = x2 ... self.y2 = y2 ... >>> def fringe8(point, rect): ... # ... ... >>> >>> point = Point(2, 2) >>> rect = Rect(1, 1, 3, 3) >>> >>> fringe8(point, rect) Is there a situation where taking two or more iterable arguments is justified? Obviously the standard itertools Python library needs that, but I can't see it being pretty in maintainable, flexible code design.

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• How can I override list methods to do vector addition and subtraction in python?

  - by Bobble

  I originally implemented this as a wrapper class around a list, but I was annoyed by the number of operator() methods I needed to provide, so I had a go at simply subclassing list. This is my test code: class CleverList(list): def __add__(self, other): copy = self[:] for i in range(len(self)): copy[i] += other[i] return copy def __sub__(self, other): copy = self[:] for i in range(len(self)): copy[i] -= other[i] return copy def __iadd__(self, other): for i in range(len(self)): self[i] += other[i] return self def __isub__(self, other): for i in range(len(self)): self[i] -= other[i] return self a = CleverList([0, 1]) b = CleverList([3, 4]) print('CleverList does vector arith: a, b, a+b, a-b = ', a, b, a+b, a-b) c = a[:] print('clone test: e = a[:]: a, e = ', a, c) c += a print('OOPS: augmented addition: c += a: a, c = ', a, c) c -= b print('OOPS: augmented subtraction: c -= b: b, c, a = ', b, c, a) Normal addition and subtraction work in the expected manner, but there are problems with the augmented addition and subtraction. Here is the output: >>> CleverList does vector arith: a, b, a+b, a-b = [0, 1] [3, 4] [3, 5] [-3, -3] clone test: e = a[:]: a, e = [0, 1] [0, 1] OOPS: augmented addition: c += a: a, c = [0, 1] [0, 1, 0, 1] Traceback (most recent call last): File "/home/bob/Documents/Python/listTest.py", line 35, in <module> c -= b TypeError: unsupported operand type(s) for -=: 'list' and 'CleverList' >>> Is there a neat and simple way to get augmented operators working in this example?

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• Simple POSIX threads question

  - by Andy

  Hi, I have this POSIX thread: void subthread(void) { while(!quit_thread) { // do something ... // don't waste cpu cycles if(!quit_thread) usleep(500); } // free resources ... // tell main thread we're done quit_thread = FALSE; } Now I want to terminate subthread() from my main thread. I've tried the following: quit_thread = TRUE; // wait until subthread() has cleaned its resources while(quit_thread); But it does not work! The while() clause does never exit although my subthread clearly sets quit_thread to FALSE after having freed its resources! If I modify my shutdown code like this: quit_thread = TRUE; // wait until subthread() has cleaned its resources while(quit_thread) usleep(10); Then everything is working fine! Could someone explain to me why the first solution does not work and why the version with usleep(10) suddenly works? I know that this is not a pretty solution. I could use semaphores/signals for this but I'd like to learn something about multithreading, so I'd like to know why my first solution doesn't work. Thanks!

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• Parallel doseq for Clojure

  - by andrew cooke

  I haven't used multithreading in Clojure at all so am unsure where to start. I have a doseq whose body can run in parallel. What I'd like is for there always to be 3 threads running (leaving 1 core free) that evaluate the body in parallel until the range is exhausted. There's no shared state, nothing complicated - the equivalent of Python's multiprocessing would be just fine. So something like: (dopar 3 [i (range 100)] ; repeated 100 times in 3 parallel threads... ...) Where should I start looking? Is there a command for this? A standard package? A good reference? So far I have found pmap, and could use that (how do I restrict to 3 at a time? looks like it uses 32 at a time - no, source says 2 + number of processors), but it seems like this is a basic primitive that should already exist somewhere. clarification: I really would like to control the number of threads. I have processes that are long-running and use a fair amount of memory, so creating a large number and hoping things work out OK isn't a good approach (example which uses a significant chunk available mem). update: Starting to write a macro that does this, and I need a semaphore (or a mutex, or an atom i can wait on). Do semaphores exist in Clojure? Or should I use a ThreadPoolExecutor? It seems odd to have to pull so much in from Java - I thought parallel programming in Clojure was supposed to be easy... Maybe I am thinking about this completely the wrong way? Hmmm. Agents?

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• synchronize threads - no UI

  - by UshaP

  I'm trying to write multithreading code and facing some synchronization questions. I know there are lots of posts here but I couldn't find anything that fits. I have a System.Timers.Timer that elapsed every 30 seconds it goes to the db and checks if there are any new jobs. If he finds one, he executes the job on the current thread (timer open new thread for every elapsed). While the job is running I need to notify the main thread (where the timer is) about the progress. Notes: I don't have UI so I can't do beginInvoke (or use background thread) as I usually do in winforms. I thought to implement ISynchronizeInvoke on my main class but that looks a little bit overkill (maybe I'm wrong here). I have an event in my job class and the main class register to it and I invoke the event whenever I need but I'm worrying it might cause blocking. Each job can take up to 20 minutes. I can have up to 20 jobs running concurrently. My question is: What is the right way to notify my main thread about any progress in my job thread? Thanks for any help.

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• Can you dynamically combine multiple conditional functions into one in Python?

  - by erich

  I'm curious if it's possible to take several conditional functions and create one function that checks them all (e.g. the way a generator takes a procedure for iterating through a series and creates an iterator). The basic usage case would be when you have a large number of conditional parameters (e.g. "max_a", "min_a", "max_b", "min_b", etc.), many of which could be blank. They would all be passed to this "function creating" function, which would then return one function that checked them all. Below is an example of a naive way of doing what I'm asking: def combining_function(max_a, min_a, max_b, min_b, ...): f_array = [] if max_a is not None: f_array.append( lambda x: x.a < max_a ) if min_a is not None: f_array.append( lambda x: x.a > min_a ) ... return lambda x: all( [ f(x) for f in f_array ] ) What I'm wondering is what is the most efficient to achieve what's being done above? It seems like executing a function call for every function in f_array would create a decent amount of overhead, but perhaps I'm engaging in premature/unnecessary optimization. Regardless, I'd be interested to see if anyone else has come across usage cases like this and how they proceeded. Also, if this isn't possible in Python, is it possible in other (perhaps more functional) languages?

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• In Ruby or Python can the very idea of Class be rewritten?

  - by John Berryman

  Howdy All... first time at stack overflow. I'm looking into using some of the metaprogramming features provided by Ruby or Python, but first I need to know the extent to which they will allow me to extend the language. The main thing I need to be able to do is to rewrite the concept of Class. This doesn't mean that I want to rewrite a specific class during run time, but rather I want to make my own conceptualization of what a Class is. To be a smidge more specific here, I want to make something that is like what people normally call a Class, but I want to follow an "open world" assumption. In the "closed world" of normal Classes, if I declare Poodle to be a subclass of Dog to be a subclass of Animal, then I know that Poodle is not going to also be a type of FurCoat. However, in an open world Class, then the Poodle object I've defined may or may not be and object of type FurCoat and we won't know for sure until I explain that I can wear the poodle. (Poor poodle.) This all has to do with a study I'm doing concerning OWL ontologies. Just so you know, I've tried to find information online, but due to the overloading of terms here I haven't found anything helpful. Super thanks, John

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• In Python, how to make sure database connection will always close before leaving a code block?

  - by Cawas

  I want to prevent database connection being open as much as possible, because this code will run on an intensive used server and people here already told me database connections should always be closed as soon as possible. def do_something_that_needs_database (): dbConnection = MySQLdb.connect(host=args['database_host'], user=args['database_user'], passwd=args['database_pass'], db=args['database_tabl'], cursorclass=MySQLdb.cursors.DictCursor) dbCursor = dbConnection.cursor() dbCursor.execute('SELECT COUNT(*) total FROM table') row = dbCursor.fetchone() if row['total'] == 0: print 'error: table have no records' dbCursor.execute('UPDATE table SET field="%s"', whatever_value) return None print 'table is ok' dbCursor.execute('UPDATE table SET field="%s"', another_value) # a lot more of workflow done here dbConnection.close() # even more stuff would come below I believe that leaves a database connection open when there is no row on the table, tho I'm still really not sure how it works. Anyway, maybe that is bad design in the sense that I could open and close a DB connection after each small block of execute. And sure, I could just add a close right before the return in that case... But how could I always properly close the DB without having to worry if I have that return, or a raise, or continue, or whatever in the middle? I'm thinking in something like a code block, similar to using try, like in the following suggestion, which obviously doesn't work: def do_something_that_needs_database (): dbConnection = MySQLdb.connect(host=args['database_host'], user=args['database_user'], passwd=args['database_pass'], db=args['database_tabl'], cursorclass=MySQLdb.cursors.DictCursor) try: dbCursor = dbConnection.cursor() dbCursor.execute('SELECT COUNT(*) total FROM table') row = dbCursor.fetchone() if row['total'] == 0: print 'error: table have no records' dbCursor.execute('UPDATE table SET field="%s"', whatever_value) return None print 'table is ok' dbCursor.execute('UPDATE table SET field="%s"', another_value) # again, that same lot of line codes done here except ExitingCodeBlock: closeDb(dbConnection) # still, that "even more stuff" from before would come below I don't think there is anything similar to ExitingCodeBlock for an exception, tho I know there is the try else, but I hope Python already have a similar feature... Or maybe someone can suggest me a paradigm move and tell me this is awful and highly advise me to never do that. Maybe this is just something to not worry about and let MySQLdb handle it, or is it?

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• Python: Calling method A from class A within class B?

  - by Tommo

  There are a number of questions that are similar to this, but none of the answers hits the spot - so please bear with me. I am trying my hardest to learn OOP using Python, but i keep running into errors (like this one) which just make me think this is all pointless and it would be easier to just use methods. Here is my code: class TheGUI(wx.Frame): def __init__(self, title, size): wx.Frame.__init__(self, None, 1, title, size=size) # The GUI is made ... textbox.TextCtrl(panel1, 1, pos=(67,7), size=(150, 20)) button1.Bind(wx.EVT_BUTTON, self.button1Click) self.Show(True) def button1Click(self, event): #It needs to do the LoadThread function! class WebParser: def LoadThread(self, thread_id): #It needs to get the contents of textbox! TheGUI = TheGUI("Text RPG", (500,500)) TheParser = WebParser TheApp.MainLoop() So the problem i am having is that the GUI class needs to use a function that is in the WebParser class, and the WebParser class needs to get text from a textbox that exists in the GUI class. I know i could do this by passing the objects around as parameters, but that seems utterly pointless, there must be a more logical way to do this that doesn't using classes seem so pointless? Thanks in advance!

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• Python : How do you find the CPU consumption for a piece of code?

  - by Yugal Jindle

  Background: I have a django application, it works and responds pretty well on low load, but on high load like 100 users/sec, it consumes 100% CPU and then due to lack of CPU slows down. Problem : Profiling the application gives me time taken by functions. This time increases on high load. Time consumed may be due to complex calculation or for waiting for CPU. so, how to find the CPU cycles consumed by a piece of code ? Since, reducing the CPU consumption will increase the response time. I might have written extremely efficient code and need to add more CPU power OR I might have some stupid code taking the CPU and causing the slow down ? Any help is appreciated ! Update: I am using Jmeter to profile my webapp, it gives me a throughput of 2 requests/sec. [ 100 users] I get a average time of 36 seconds on 100 request vs 1.25 sec time on 1 request. More Info Configuration Nginx + Uwsgi with 4 workers No database used, using a responses from a REST API On 1st hit the response of REST API gets cached, therefore doesn't makes a difference. Using ujson for json parsing. Curious to Know: Python-Django is used by so many orgs for so many big sites, then there must be some high end Debug / Memory-CPU analysis tools. All those I found were casual snippets of code that perform profiling.

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• How do I subtract two dates in Django/Python?

  - by Ryan

  Hi! I'm working on a little fitness tracker in order to teach myself Django. I want to graph my weight over time, so I've decided to use the Python Google Charts Wrapper. Google charts require that you convert your date into a x coordinate. To do this I want to take the number of days in my dataset by subtracting the first weigh-in from the last weigh-in and then using that to figure out the x coords (for example, I could 100 by the result and increment the x coord by the resulting number for each y coord.) Anyway, I need to figure out how to subtract Django datetime objects from one another and so far, I am striking out on both google and here at the stack. I know PHP, but have never gotten a handle on OO programming, so please excuse my ignorance. Here is what my models look like: class Goal(models.Model): goal_weight = models.DecimalField("Goal Weight",max_digits=4, decimal_places=1) target_date = models.DateTimeField("Target Date to Reach Goal") set_date = models.DateTimeField("When did you set your goal?") comments = models.TextField(blank=True) def __unicode__(self): return unicode(self.goal_weight) class Weight(models.Model): """Weight at a given date and time """ goal = models.ForeignKey(Goal) weight = models.DecimalField("Current Weight",max_digits=4, decimal_places=1) weigh_date = models.DateTimeField("Date of Weigh-In") comments = models.TextField(blank=True) def __unicode__(self): return unicode(self.weight) def recorded_today(self): return self.date.date() == datetime.date.today() Any ideas on how to proceed in the view? Thanks so much!

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