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OpenCV 2.0 and Python

- by Jive Dadson

I cannot get the example Python programs to run. When executing the Python command "from opencv import cv" I get the message "ImportError: No module named _cv". There is a stale _cv.pyd in the site-packages directory, but no _cv.py anywhere. See step 5 below. MS Windows XP, VC++ 2008, Python 2.6, OpenCV 2.0 Here's what I have done. Downloaded and ran the MS Windows installer for OpenCV2.0. Downloaded and installed CMake Downloaded and installed SWIG Ran CMake. After unchecking "ENABLE_OPENMP" in the CMake GUI, I was able to build OpenCV using INSTALL.vcproj and BUILD_ALL.vcproj. I do not know what the difference is, so I built everything under both of those project files. The C example programs run fine. Copied contents of OpenCV2.0/Python2.6/lib/site-packages to my installed Python2.6/lib/site-packages directory. I notice that it contains an old _cv.pyd and an old libcv.dll.a.

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Python imaging alternatives

- by Paul McMillan

I have python code that needs to do just a couple simple things to photographs: crop, resize, and overlay a watermark. I've used PIL, and the resample/resize results are TERRIBLE. I've used imagemagick, and the interface and commands were designed by packaging a cat in a box, and then repeatedly throwing it down a set of stairs at a keyboard. I'm looking for something which is not PIL or Imagemagick that I can use with python to do simple, high-quality image transformations. For that matter, it doesn't even have to have python bindings if the command line interface is good. Oh, and it needs to be relatively platform agnostic, our production servers are linux, but some of our devs develop on windows. It can't require the installation of a bunch of silly gui code to use as a library, either.

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Pointer argument to boost python

- by piotr

What's the best way to make a function that has pointer as argument work with boost python? I see there are many possibilities for return values in the docs, but I don't know how to do it with arguments. void Tesuto::testp(std::string* s) { if (!s) cout << " NULL s" << endl; else cout << s << endl; } >>> t.testp(None) NULL s >>> >>> s='test' >>> t.testp(s) Traceback (most recent call last): File "<stdin>", line 1, in <module> Boost.Python.ArgumentError: Python argument types in Tesuto.testp(Tesuto, str) did not match C++ signature: testp(Tesuto {lvalue}, std::string*) >>>

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functional-style datatypes in Python

- by Danny Roberts

For anyone who's spent some time with sml, ocaml, haskell, etc. when you go back to using C, Python, Java, etc. you start to notice things you never knew were missing. I'm doing some stuff in Python and I realized what I really want is a functional-style datatype like (for example) datatype phoneme = Vowel of string | Consonant of voice * place * manner datatype voice = Voiced | Voiceless datatype place = Labial | Dental | Retroflex | Palatal | Velar | Glottal datatype manner = Stop | Affricate | Fricative | Nasal | Lateral type syllable = phoneme list Does anyone have a particular way that they like to simulate this in Python?

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How to parse malformed HTML in python, using standard libraries

- by bukzor

There are so many html and xml libraries built into python, that it's hard to believe there's no support for real-world HTML parsing. I've found plenty of great third-party libraries for this task, but this question is about the python standard library. Requirements: Use only Python standard library components (I'm currently using v2.6) DOM support Handle HTML entities ( ) Handle partial documents (like: Hello, <iWorld</i!) Bonus points: XPATH support Handle unclosed/malformed tags. (<bigdoes anyone here know <html ???

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Python regular expression implementation details

- by Tom

A question that I answered got me wondering: How are regular expressions implemented in Python? What sort of efficiency guarantees are there? Is the implementation "standard", or is it subject to change? I thought that regular expressions would be implemented as DFAs, and therefore were very efficient (requiring at most one scan of the input string). Laurence Gonsalves raised an interesting point that not all Python regular expressions are regular. (His example is r"(a+)b\1", which matches some number of a's, a b, and then the same number of a's as before). This clearly cannot be implemented with a DFA. So, to reiterate: what are the implementation details and guarantees of Python regular expressions? It would also be nice if someone could give some sort of explanation (in light of the implementation) as to why the regular expressions "cat|catdog" and "catdog|cat" lead to different search results in the string "catdog", as mentioned in the question that I referenced before.

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Python and Postgresql

- by Ian

Hi all, if you wanted to manipulate the data in a table in a postgresql database using some python (maybe running a little analysis on the result set using scipy) and then wanted to export that data back into another table in the same database, how would you go about the implementation? Is the only/best way to do this to simply run the query, have python store it in an array, manipulate the array in python and then run another sql statement to output to the database? I'm really just asking, is there a more efficient way to deal with the data? Thanks, Ian

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Newbie Python programmer tangling with Lists.

- by Sergio Tapia

Here's what I've got so far: # A. match_ends # Given a list of strings, return the count of the number of # strings where the string length is 2 or more and the first # and last chars of the string are the same. # Note: python does not have a ++ operator, but += works. def match_ends(words): counter = 0 for word in words: if len(word) >= 2 and word[0] == word[-1]: counter += counter return counter # +++your code here+++ return I'm following the Google Python Class, so this isn't homework, but me just learning and improving myself; so please no negative comments about 'not doing my homework'. :P What do you guys think I'm doing wrong here? Here's the result: match_ends X got: 0 expected: 3 X got: 0 expected: 2 X got: 0 expected: 1 I'm really loving Python, so I just know that I'll get better at it. :)

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Getting Started with Python: Attribute Error

- by Nacari

I am new to python and just downloaded it today. I am using it to work on a web spider, so to test it out and make sure everything was working, I downloaded a sample code. Unfortunately, it does not work and gives me the error: "AttributeError: 'MyShell' object has no attribute 'loaded' " I am not sure if the code its self has an error or I failed to do something correctly when installing python. Is there anything you have to do when installing python like adding environmental variables, etc.? And what does that error generally mean? Here is the sample code I used with imported spider class: import chilkat spider = chilkat.CkSpider() spider.Initialize("www.chilkatsoft.com") spider.AddUnspidered("http://www.chilkatsoft.com/") for i in range(0,10): success = spider.CrawlNext() if (success == True): print spider.lastUrl() else: if (spider.get_NumUnspidered() == 0): print "No more URLs to spider" else: print spider.lastErrorText() # Sleep 1 second before spidering the next URL. spider.SleepMs(1000)

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Python 3.1.1 Problem With Tuples

- by Protean

This piece of code is supposed to go through a list and preform some formatting to the items, such as removing quotations, and then saving it to another list. class process: def rchr(string_i, asciivalue): string_o = () for i in range(len(string_i)): if ord(string_i[i]) != asciivalue: string_o += string_i[i] return string_o def flist(self, list_i): cache = () cache_list = [] for line in list_i: cache = line.split('\t') cacbe[0] = process.rchr(str(cache[0]), 34) cache_list.append(cache[0]) cache_list[index] = cache index += 1 cache_list.sort() return cache_list p = process() list1a = ['cow', 'dog', '"sheep"'] list1 = p.flist(list1a) print (country_list) However; it chokes at 'string_o += string_i[i]' and gives the following error: Traceback (most recent call last): File "/Projects/Python/safafa.py", line 23, in <module> list1 = p.flist(list1a) File "/Projects/Python/safafa.py", line 14, in flist cacbe[0] = process.rchr(str(cache[0]), 34) File "/Projects/Python/safafa.py", line 7, in rchr string_o += string_i[i] TypeError: can only concatenate tuple (not "str") to tuple

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ungetc in Python

- by Dragos Toader

Some file read (readlines()) functions in Python copy the file contents to memory (as a list) I need to process a file that's too large to be copied in memory and as such need to use a file pointer (to access the file one byte at a time) -- as in C getc(). The additional requirement I have is that I'd like to rewind the file pointer to previous bytes like in C ungetc(). Is there a way to do this in Python? Also, in Python, I can read one line at a time with readline() Is there a way to read the previous line going backward?

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Reverse Engineer a .pyo python file

- by Brian

I have 2 .pyo python files that I can convert to .py source files, but they don't compile perfectly as hinted by decompyle's verify. Therefore looking at the source code, I can tell that config.pyo simply had variables in in an array: ADMIN_USERIDS = [116901, 141, 349244, 39, 1159488] I would like to take the original .pyo and disassembly or whatever I need to do inorder to change one of these IDs. Or.... in model.pyo the source indicates a if (productsDeveloperId != self.getUserId()): All I would want to do is hex edit the != to be a == .....Simple with a windows exe program but I can't find a good python disassembler anywhere. Any suggestions are welcomed...I am new to reading bytecode and new to python as well.

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Is it possible to distribute STDIN over parallel processes?

- by Erik

Given the following example input on STDIN: foo bar bar baz === qux bla === def zzz yyy Is it possible to split it on the delimiter (in this case '===') and feed it over stdin to a command running in parallel? So the example input above would result in 3 parallel processes (for example a command called do.sh) where each instance received a part of the data on STDIN, like this: do.sh (instance 1) receives this over STDIN: foo bar bar baz do.sh (instance 2) receives this over STDIN: qux bla do.sh (instance 3) receives this over STDIN: def zzz yyy I suppose something like this is possible using xargs or GNU parallel, but I do not know how.

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Python: Why is IDLE so slow?

- by Adam Matan

Hi, IDLE is my favorite Python editor. It offers very nice and intuitive Python shell which is extremely useful for unit-testing and debugging, and a neat debugger. However, code executed under IDLE is insanely slow. By insanely I mean 3 orders of magnitude slow: bash time echo "for i in range(10000): print 'x'," | python Takes 0.052s, IDLE import datetime start=datetime.datetime.now() for i in range(10000): print 'x', end=datetime.datetime.now() print end-start Takes: >>> 0:01:44.853951 Which is roughly 2,000 times slower. Any thoughts, or ideas how to improve this? I guess it has something to do with the debugger in the background, but I'm not really sure. Adam

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Python (windows) will open files from command line, but not from a script launched from eclipse

- by Blake

I'm pretty new to writing python for windows (linux is no problem), and am having problems getting python to recognize files when running scripts, though it behaves fine in the command line What am I doing wrong here? def verifyFile(x): # return os.path.isfile(x) This will return true (with a valid file, of course) when called from the python command line, but when I run the script from eclipse, or launch it from windows, it ALWAYS returns false. Any thoughts on why this is? I've tried passing pathnames like this: D:\Documents and Settings\BDE\Desktop\cdburn.jpg and like this: D:/Documents and Settings/BDE/Desktop/cdburn.jpg I've changed sys,argv[0] to '' I've tried this: def verifyFile(x): # try: f = open(x, 'r') f.close() return True except: return False and am getting no love! Any help would be appreciated. Thanks Blake

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How do I use Python's itertools.groupby()?

- by James Sulak

I haven't been able to find an understandable explanation of how to actually use Python's itertools.groupby() function. What I'm trying to do is this: take a list - in this case, the children of an objectified lxml element - divide it into groups based on some criteria, and then later iterate over each of these groups separately. I've reviewed the documentation (http://docs.python.org/lib/itertools-functions.html), and the examples, (http://docs.python.org/lib/itertools-example.html), but I've had trouble trying to apply them beyond a simple list of numbers. So, how do I use of itertools.groupby()? Is there another technique I should be using? Pointers to good "prerequisite" reading would also be appreciated.

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object won't die (still references to it that I can't find)

- by user288558

I'm using parallel-python and start a new job server in a function. after the functions ends it still exists even though I didn't return it out of the function (I used weakref to test this). I guess there's still some references to this object somewhere. My two theories: It starts threads and it logs to root logger. My questions: can I somehow findout in which namespace there is still a reference to this object. I have the weakref reference. Does anyone know how to detach a logger? What other debug suggestions do people have? here is my testcode: def pptester(): js=pp.Server(ppservers=nodes) js.set_ncpus(0) fh=file('tmp.tmp.tmp','w') tmp=[] for i in range(200): tmp.append(js.submit(ppworktest,(),(),('os','subprocess'))) js.print_stats() return weakref.ref(js) thanks in advance Wolfgang

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AES Encryption. From Python (pyCrypto) to .NET

- by Why

I am currently trying to port a legacy Python app over to .NET which contains AES encrpytion using from what I can tell pyCrpyto. I have very limited Python and Crypto experience. The code uses the snippet from the following page. http://www.djangosnippets.org/snippets/1095/ So far I believe I have managed to work out that it that it calls Crypto.Cipher with AES and the first 32 character of our secret key as the password, but no mode or IV. It also puts a prefix on the encrpyed text when it is added to database. What I can't work out is how I can decrypt the existing ecrypted database records in .NET. I have been looking at RijndaelManaged but it requires an IV and can't see any reference to one in python. Can anyone point me in the dirrection to what method could be used in .NET to get the desired result.

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Where has my parallel port gone? ioperm(888,1,1) returns -1.

- by marcusw

I have an old Dell Dimension 8200 running Gentoo which I use solely to control various things using the parallel port. After shutting it down a few weeks ago, I started it up again today and tried to access the parallel port like I usually do. Unfortunately, my code bombed out when it tried to call ioperm(888,1,1) to grab the parallel port which returned an error code of -1. There have been no changes to the system be it hardware or software, no updates, no tweaking, no dropping the case, no over-amping the data pins, nothing. The port and the software have been working fine for months with no changes, and were working fine when I shut it down last. Running my code with root privileges changes nothing. What is breaking this and how can I fix it?

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RabbitMQ serializing messages from queue with multiple consumers

- by Refefer

Hi there, I'm having a problem where I have a queue set up in shared mode and multiple consumers bound to it. The issue is that it appears that rabbitmq is serializing the messages, that is, only one consumer at a time is able to run. I need this to be parallel, however, I can't seem to figure out how. Each consumer is running in its own process. There are plenty of messages in the queue. I'm using py-amqplib to interface with RabbitMQ. Any thoughts?

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Pre-generating GUIDs for use in python?

- by rjuiaa1

I have a python program that needs to generate several guids and hand them back with some other data to a client over the network. It may be hit with a lot of requests in a short time period and I would like the latency to be as low as reasonably possible. Ideally, rather than generating new guids on the fly as the client waits for a response, I would rather be bulk-generating a list of guids in the background that is continually replenished so that I always have pre-generated ones ready to hand out. I am using the uuid module in python on linux. I understand that this is using the uuidd daemon to get uuids. Does uuidd already take care of pre-genreating uuids so that it always has some ready? From the documentation it appears that it does not. Is there some setting in python or with uuidd to get it to do this automatically? Is there a more elegant approach then manually creating a background thread in my program that maintains a list of uuids?

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how to install mysqlDb for MySQL and Python ON WINDOWS

- by Spikie

I AM A NET DEVELOPER TRY TO INSTALL MYSQLDB FOR PYTHON I KEEP HAVING THIS ERROR MESSAGE raise ImproperlyConfigured("Error loading MySQLdb module: %s" % e) django.core.exceptions.ImproperlyConfigured: Error loading MySQLdb module: No module named MySQLdb I AM FOLLOWING THIS INSTRUCTION FROM THIS SITE <"http://sourceforge.net/project/shownotes.php?release_id=303257" I DO NOT UNDERSTAND THESE LINES Windows ....... C:... python setup.py install C:... python setup.py bdist_wininst The latter example should build a Windows installer package, if you have the correct tools. In any event, you must have a C compiler. Additionally, you have to set an environment variable (mysqlroot) which is the path to your MySQL installation. In theory, it would be possible to get this information out of the registry, but like I said, I don't do Windows, but I'll accept a patch that does this. I HAVE BEEN SEARCHING FOR ANSWER ALL DAY PLEASE DO ANYBODY REALLY KNOW HOW TO DO THIS OR AT LEAST POINT ME IN THE RIGHT DIRECTION???? THANKS and what is the c compiler for???????

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Installing bitarray in Python 2.6 on Windows

- by John Fouhy

I would like to install bitarray in Windows running python 2.6. I have mingw32 installed, and I have C:\Python26\Lib\distutils\distutils.cfg set to: [build] compiler = mingw32 If I type, in a cmd.exe window: C:\Documents and Settings\john\My Documents\bitarray-0.3.5>python setup.py install I get: [normal python messages skipped] C:\MinGW\bin\gcc.exe -mno-cygwin -mdll -O -Wall -IC:\Python26\include -IC:\Python26\PC -c bitarray/_bitarray.c -o build\temp.win32-2.6\Release\bitarray\_bitarray.o bitarray/_bitarray.c:2197: error: initializer element is not constant bitarray/_bitarray.c:2197: error: (near initialization for `BitarrayIter_Type.tp_getattro') bitarray/_bitarray.c:2206: error: initializer element is not constant bitarray/_bitarray.c:2206: error: (near initialization for `BitarrayIter_Type.tp_iter') bitarray/_bitarray.c:2232: error: initializer element is not constant bitarray/_bitarray.c:2232: error: (near initialization for `Bitarraytype.tp_getattro') bitarray/_bitarray.c:2253: error: initializer element is not constant bitarray/_bitarray.c:2253: error: (near initialization for `Bitarraytype.tp_alloc') bitarray/_bitarray.c:2255: error: initializer element is not constant bitarray/_bitarray.c:2255: error: (near initialization for `Bitarraytype.tp_free') error: command 'gcc' failed with exit status 1 Can anyone help?

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Python Bitstream implementations

- by Danielb

I am writing a huffman implementation in Python as a learning exercise. I have got to the point of writing out my variable length huffman codes to a buffer (or file). Only to find there does not seem to be a bitstream class implemented by Python! I have had a look at the array and struct modules but they do not seem to do what I need without extra work. A bit of goggling turned up this bitstream implementation, which is more like what I am wanting. Is there really no comparable bitstream class in the Python standard library?

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problems importing ttk from tkinter in python 2.7

- by Benjimin Boyce

I'm working with an example file in a tutorial that asks me to first do two imports: from tkinter import * from tkinter import ttk I get an error. I researched a bit and found that in python 2.7.x I need to capitalize the 't'in tkinter, so I change to: from Tkinter import * from Tkinter import ttk. the first line no longer gives and error, but I still get error: ImportError: cannot import name ttk. I have researched this issue on this site and other places, and cannot seem to understand what this ttk is. I'm further confused by the fact that, when I go to the python interpreter, and I type "help()", then "modules", and then "ttk" it seems to know what it is, and gives me a lot of description, for example: "DESCRIPTION This module provides classes to allow using Tk themed widget set." -however, python won't let me import it.

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