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  • python convert 12 bit image encoded in a string to 8 bit png

    - by ks
    I have a string that is read from a usb apogee camera that is a 12-bit grayscale image with the 12-bits each occupying the lowest 12 bits of 16-bits words. I want to create a 8-bit png from this string by ignoring the lowest 4 bits. I can convert it to a 16-bit image where the highest 4 bits are always zero using PIL with import Image imageStr is the image string imageSize is the image size img=Image.fromstring("I", imageSize, imageStr, "raw", "I;16", 0,1) img.save("MyImage.png", "PNG") Anyway I can do something similar to create a 8-bit image without completely unpacking the string doing arithmetic and making a new string?

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  • undo or reverse argsort(), python

    - by Vincent
    Given an array 'a' I would like to sort the array by columns "a.sort(axis=0)" do some stuff to the array and then undo the sort. By that I don't mean re sort but basically reversing how each element was moved. I assume argsort() is what I need but it is not clear to me how to sort an array with the results of argsort() or more importantly apply the reverse/inverse of argsort() Here is a little more detail I have an array a, shape(a) = rXc I need to sort each column aargsort = a.argsort(axis=0) # May use this later aSort = a.sort(axis=0) now average each row aSortRM = asort.mean(axis=1) now replace each col in a row with the row mean. is there a better way than this aWithMeans = ones_like(a) for ind in range(r) # r = number of rows aWithMeans[ind]* aSortRM[ind] Now I need to undo the sort I did in the first step. ????

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  • Python: How to transfer varrying length arrays over a network connection

    - by Devin
    Hi, I need to transfer an array of varying length in which each element is a tuple of two integers. As an example: path = [(1,1),(1,2)] path = [(1,1),(1,2),(2,2)] I am trying to use pack and unpack, however, since the array is of varying length I don't know how to create a format such that both know the format. I was trying to turn it into a single string with delimiters, such as: msg = 1&1~1&2~ sendMsg = pack("s",msg) or sendMsg = pack("s",str(msg)) on the receiving side: path = unpack("s",msg) but that just prints 1 in this case. I was also trying to send 4 integers as well, which send and receive fine, so long as I don't include the extra string representing the path. sendMsg = pack("hhhh",p.direction[0],p.direction[1],p.id,p.health) on the receive side: x,y,id,health = unpack("hhhh",msg) The first was for illustration as I was trying to send the format "hhhhs", but either way the path doesn't come through properly. Thank-you for your help. I will also be looking at sending a 2D array of ints, but I can't seem to figure out how to send these more 'complex' structures across the network. Thank-you for your help.

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  • regex in python, can this be improved upon?

    - by tipu
    I have this piece of code that finds words that begin with @ or #, p = re.findall(r'@\w+|#\w+', str) Now what irks me about this is repeating \w+. I am sure there is a way to do something like p = re.findall(r'(@|#)\w+', str) That will produce the same result but it doesn't, it instead returns only # and @. How can that regex be changed so that I am not repeating the \w+? This code comes close, p = re.findall(r'((@|#)\w+)', str) But it returns [('@many', '@'), ('@this', '@'), ('#tweet', '#')] (notice the extra '@', '@', and '#'.

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  • deleting unaccessed files using python

    - by damon
    My django app parses some files uploaded by the user.It is possible that the file uploaded by the user may remain in the server for a long time ,without it being parsed by the app.This can increase in size if a lot of users upload a lot of files. I need to delete those files not recently parsed by the app -say not accessed for last 24 hours.I tried like this import os import time dirname = MEDIA_ROOT+my_folder filenames = os.listdir(dirname) filenames = [os.path.join(dirname,filename) for filename in filenames] for filename in filenames: last_access = os.stat(filename).st_atime #secs since epoch rtime = time.asctime(time.localtime(last_access)) print filename+'----'+rtime This shows the last accessed times for each file..But I am not sure how I can test if the file access time was within the last 24 hours..Can somebody help me out?

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  • Efficient way to access a mapping of identifiers in Python

    - by sixbelo
    I am writing an app to do a file conversion and part of that is replacing old account numbers with a new account numbers. Right now I have a CSV file mapping the old and new account numbers with around 30K records. I read this in and store it as dict and when writing the new file grab the new account from the dict by key. My question is what is the best way to do this if the CSV file increases to 100K+ records? Would it be more efficient to convert the account mappings from a CSV to a sqlite database rather than storing them as a dict in memory?

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  • merging indexed array in Python

    - by leon
    Suppose that I have two numpy arrays of the form x = [[1,2] [2,4] [3,6] [4,NaN] [5,10]] y = [[0,-5] [1,0] [2,5] [5,20] [6,25]] is there an efficient way to merge them such that I have xmy = [[0, NaN, -5 ] [1, 2, 0 ] [2, 4, 5 ] [3, 6, NaN] [4, NaN, NaN] [5, 10, 20 ] [6, NaN, 25 ] I can implement a simple function using search to find the index but this is not elegant and potentially inefficient for a lot of arrays and large dimensions. Any pointer is appreciated.

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  • Overriding Built-in Classes (Python)

    - by Yipeng
    How can I view and override the full definition for built in classes? I have seen the library docs but am looking for something more. For e.g. is it possible to override the Array Class such that the base index starts from 1 instead of 0, or to override .sort() of list to a sorting algorithm of my own liking?

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  • How do you create a daemon in Python?

    - by DavidM
    Searching on Google reveals x2 code snippets. The first result is to this code recipe which has a lot of documentation and explanation, along with some useful discussion underneath. However, another code sample, whilst not containing so much documentation, includes sample code for passing commands such as start, stop and restart. It also creates a PID file which can be handy for checking if the daemon is already running etc. These samples both explain how to create the daemon. Are there any additional things that need to be considered? Is one sample better than the other, and why?

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  • Difference Between Two Lists with Many Duplicates in Python

    - by Paul
    I have several lists that contain many of the same items and many duplicate items. I want to check which items in one list are not in the other list. For example, I might have one list like this: l1 = ['a', 'b', 'c', 'b', 'c'] and one list like this: l2 = ['a', 'b', 'c', 'b'] Comparing these two lists I would want to return a third list like this: l3 = ['c'] I am currently using some terrible code that I made a while ago that I'm fairly certain doesn't even work properly shown below. def list_difference(l1,l2): for i in range(0, len(l1)): for j in range(0, len(l2)): if l1[i] == l1[j]: l1[i] = 'damn' l2[j] = 'damn' l3 = [] for item in l1: if item!='damn': l3.append(item) return l3 How can I better accomplish this task?

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  • Python lxml - returns null list

    - by Chris Finlayson
    I cannot figure out what is wrong with the XPATH when trying to extract a value from a webpage table. The method seems correct as I can extract the page title and other attributes, but I cannot extract the third value, it always returns an empty list? from lxml import html import requests test_url = 'SC312226' page = ('https://www.opencompany.co.uk/company/'+test_url) print 'Now searching URL: '+page data = requests.get(page) tree = html.fromstring(data.text) print tree.xpath('//title/text()') # Get page title print tree.xpath('//a/@href') # Get href attribute of all links print tree.xpath('//*[@id="financial"]/table/tbody/tr/td[1]/table/tbody/tr[2]/td[1]/div[2]/text()') Unless i'm missing something, it would appear the XPATH is correct: Chrome screenshot I checked Chrome console, appears ok! So i'm at a loss $x ('//*[@id="financial"]/table/tbody/tr/td[1]/table/tbody/tr[2]/td[1]/div[2]/text()') [ "£432,272" ]

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  • most widely used python web app deployment style

    - by mete
    I wonder which option is more stable (leaving performance aside) and is more widely used (I assume the widely used one is the most stable): apache - mod_wsgi apache - mod_fcgid apache - mod_proxy_ajp apache - mod_proxy_http for a project that will serve REST services with small json formatted input and output messages and web pages, up to 100 req/s. Please comment on apache if you think nginx etc. is more suitable. Thanks.

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  • Simple check authentication decorator in Python + Pylons

    - by ensnare
    I'd like to write a simple decorator that I can put above functions in my controller to check authentication and re-direct to the login page if the current user is not authenticated. What is the best way to do this? Where should the decorator go? How should I pass cookie info to the decorator? Sample code is greatly appreciated. Thank you!

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  • python dict.fromkeys() returns empty

    - by slooow
    I wrote the following function. It returns an empty dictionary when it should not. The code works on the command line without function. However I cannot see what is wrong with the function, so I have to appeal to your collective intelligence. def enter_users_into_dict(userlist): newusr = {} newusr.fromkeys(userlist, 0) return newusr ul = ['john', 'mabel'] nd = enter_users_into_dict(ul) print nd It returns an empty dict {} where I would expect {'john': 0, 'mabel': 0}. It is probably very simply but I don't see the solution.

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  • Object for storing strings in Python

    - by evg
    class MyWriter: def __init__(self, stdout): self.stdout = stdout self.dumps = [] def write(self, text): self.stdout.write(smart_unicode(text).encode('cp1251')) self.dumps.append(text) def close(self): self.stdout.close() writer = MyWriter(sys.stdout) save = sys.stdout sys.stdout = writer I use self.dumps list to store data obtained from prints. Is there a more convenient object for storing string lines in memory? Ideally I want dump it to one big string. I can get it like this "\n".join(self.dumps) from code above. May be it's better to just concatenate strings - self.dumps += text?

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  • Python metaclass to run a class method automatically on derived class

    - by Barry Steyn
    I want to automatically run a class method defined in a base class on any derived class during the creation of the class. For instance: class Base(object): @classmethod def runme(): print "I am being run" def __metclass__(cls,parents,attributes): clsObj = type(cls,parents,attributes) clsObj.runme() return clsObj class Derived(Base): pass: What happens here is that when Base is created, ''runme()'' will fire. But nothing happens when Derived is created. The question is: How can I make ''runme()'' also fire when creating Derived. This is what I have thought so far: If I explicitly set Derived's metclass to Base's, it will work. But I don't want that to happen. I basically want Derived to use the Base's metaclass without me having to explicitly set it so.

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  • debugging Python program

    - by challarao
    I have created some program for this.But printed a,b,c values are not correct.Please check this whether it is correct or not? n=input("Enter the no.of McNuggets:") a,b,c=0,0,0 count=0 for a in range(n): if 6*a+9*b+20*c==n: count=count+1 break else: for b in range(n): if 6*a+9*b+20*c==n: count=count+1 break else: for c in range(n): if 6*a+9*b+20*c==n: count=count+1 break if count>0: print "It is possible to buy exactly",n,"packs of McNuggetss",a,b,c else: print "It is not possible to buy"

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  • Skip subdirectory in python import

    - by jstaab
    Ok, so I'm trying to change this: app/ - lib.py - models.py - blah.py Into this: app/ - __init__.py - lib.py - models/ - __init__.py - user.py - account.py - banana.py - blah.py And still be able to import my models using from app.models import User rather than having to change it to from app.models.user import User all over the place. Basically, I want everything to treat the package as a single module, but be able to navigate the code in separate files for development ease. The reason I can't do something like add for file in __all__: from file import * into init.py is I have circular references between the model files. A fix I don't want is to import those models from within the functions that use them. But that's super ugly. Let me give you an example: user.py ... from app.models import Banana ... banana.py ... from app.models import User ... I wrote a quick pre-processing script that grabs all the files, re-writes them to put imports at the top, and puts it into models.py, but that's hardly an improvement, since now my stack traces don't show the line number I actually need to change. Any ideas? I always though init was probably magical but now that I dig into it, I can't find anything that lets me provide myself this really simple convenience.

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