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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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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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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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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 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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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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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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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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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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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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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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deciding between subprocess, multiprocesser and thread in Python?

- by user248237

I'd like to parallelize my Python program so that it can make use of multiple processors on the machine that it runs on. My parallelization is very simple, in that all the parallel "threads" of the program are independent and write their output to separate files. I don't need the threads to exchange information but it is imperative that I know when the threads finish since some steps of my pipeline depend on their output. Portability is important, in that I'd like this to run on any Python version on Mac, Linux and Windows. Given these constraints, which is the most appropriate Python module for implementing this? I am tryign to decide between thread, subprocess and multiprocessing, which all seem to provide related functionality. Any thoughts on this? I'd like the simplest solution that's portable. Thanks.

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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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Inaccurate Logarithm in Python

- by Avihu Turzion

I work daily with Python 2.4 at my company. I used the versatile logarithm function 'log' from the standard math library, and when I entered log(2**31, 2) it returned 31.000000000000004, which struck me as a bit odd. I did the same thing with other powers of 2, and it worked perfectly. I ran 'log10(2**31) / log10(2)' and I got a round 31.0 I tried running the same original function in Python 3.0.1, assuming that it was fixed in a more advanced version. Why does this happen? Is it possible that there are some inaccuracies in mathematical functions in Python?

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What Python based Dashboard options exist?

- by stuartcw

I want to create a Dashboard on each server to show it's health and the results of some daily processing. I plan to hook up shell scripts and Python programs to collect the data. Instead of writing a web-based interface, I thought it would be good to use a python based web dashboard that could render the results in various business user and manager friendly formats. What are my options to do this? I am primarily interested in Python RedHat Linux, but other platforms are interesting too. I'm also open to Perl and Ruby based solutions especially if the plugins can be language neutral.

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Parallelism in Python

- by fmark

What are the options for achieving parallelism in Python? I want to perform a bunch of CPU bound calculations over some very large rasters, and would like to parallelise them. Coming from a C background, I am familiar with three approaches to parallelism: Message passing processes, possibly distributed across a cluster, e.g. MPI. Explicit shared memory parallelism, either using pthreads or fork(), pipe(), et. al Implicit shared memory parallelism, using OpenMP. Deciding on an approach to use is an exercise in trade-offs. In Python, what approaches are available and what are their characteristics? Is there a clusterable MPI clone? What are the preferred ways of achieving shared memory parallelism? I have heard reference to problems with the GIL, as well as references to tasklets. In short, what do I need to know about the different parallelization strategies in Python before choosing between them?

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How to prevent traffic to/from a slow Cassandra node using Python

- by Sergio Ayestarán

Intro: I have a Python application using a Cassandra 1.2.4 cluster with a replication factor of 3, all reads and writes are done with a consistency level of 2. To access the cluster I use the CQL library. The Cassandra cluster is running on rackspace's virtual servers. The problem: From time to time one of the nodes can become slower than usual, in this case I want to be able to detect this situation and prevent making requests to the slow node and if possible to stop using it at all (this should theoretically be possible since the RF is 3 and the CL is 2 for every single request). The questions: What's the best way of detecting the slow node from a Python application? Is there a way to stop using one of the Cassandra nodes from Python in this scenario without human intervention? Thanks in advance!

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python xml.dom.minidom.Attr question

- by rudy

Getting attributes using minidom in Python, one uses the "attributes" property. e.g. node.attributes["id"].value So if I have <a id="foo"></a>, that should give me "foo". node.attributes["id"] does not return the value of the named attribute, but an xml.dom.minidom.Attr instance. But looking at the help for Attr, by doing help('xml.dom.minidom.Attr'), nowhere is this magic "value" property mentioned. I like to learn APIs by looking at the type hierarchy, instance methods etc. Where did this "value" property come from?? Why is it not listed in the Attr class' page? The only data descriptors mentioned are isId, localName and schemaType. Its also not inherited from any superclasses. Since I'm new to Python, would some of the Python gurus enlighten?

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