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  • Finding the intersection of two vector equations.

    - by Matthew Mitchell
    I've been trying to solve this and I found an equation that gives the possibility of zero division errors. Not the best thing: v1 = (a,b) v2 = (c,d) d1 = (e,f) d2 = (h,i) l1: v1 + ?d1 l2: v2 + µd2 Equation to find vector intersection of l1 and l2 programatically by re-arranging for lambda. (a,b) + ?(e,f) = (c,d) + µ(h,i) a + ?e = c + µh b +?f = d + µi µh = a + ?e - c µi = b +?f - d µ = (a + ?e - c)/h µ = (b +?f - d)/i (a + ?e - c)/h = (b +?f - d)/i a/h + ?e/h - c/h = b/i +?f/i - d/i ?e/h - ?f/i = (b/i - d/i) - (a/h - c/h) ?(e/h - f/i) = (b - d)/i - (a - c)/h ? = ((b - d)/i - (a - c)/h)/(e/h - f/i) Intersection vector = (a + ?e,b + ?f) Not sure if it would even work in some cases. I haven't tested it. I need to know how to do this for values as in that example a-i. Thank you.

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  • Convert args to flat list?

    - by Mark
    I know this is very similar to a few other questions, but I can't quite get this function to work correctly. def flatten(*args): return list(item for iterable in args for item in iterable) The output I'm looking for is: flatten(1) -> [1] flatten(1,[2]) -> [1, 2] flatten([1,[2]]) -> [1, 2] The current function, which I from another SO answer doesn't seem to produce correct results at all: >>> flatten([1,[2]]) [1, [2]] I wrote the following function which seems to work for 0 or 1 levels of nesting, but not deeper: def flatten(*args): output = [] for arg in args: if hasattr(arg, '__iter__'): output += arg else: output += [arg] return output

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  • How do I store multiple copies of the same field in Django?

    - by Alistair
    I'm storing OLAC metadata which describes linguistic resources. Many of the elements of the metadata are repeatable -- for example, a resource can have two languages, three authors and four dates associated with it. Is there any way of storing this in one model? It seems like overkill to define a model for each repeatable metadata element -- especially since the models will only have one field: it's value.

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  • Combinatorial optimisation of a distance metric

    - by Jose
    I have a set of trajectories, made up of points along the trajectory, and with the coordinates associated with each point. I store these in a 3d array ( trajectory, point, param). I want to find the set of r trajectories that have the maximum accumulated distance between the possible pairwise combinations of these trajectories. My first attempt, which I think is working looks like this: max_dist = 0 for h in itertools.combinations ( xrange(num_traj), r): for (m,l) in itertools.combinations (h, 2): accum = 0. for ( i, j ) in itertools.izip ( range(k), range(k) ): A = [ (my_mat[m, i, z] - my_mat[l, j, z])**2 \ for z in xrange(k) ] A = numpy.array( numpy.sqrt (A) ).sum() accum += A if max_dist < accum: selected_trajectories = h This takes forever, as num_traj can be around 500-1000, and r can be around 5-20. k is arbitrary, but can typically be up to 50. Trying to be super-clever, I have put everything into two nested list comprehensions, making heavy use of itertools: chunk = [[ numpy.sqrt((my_mat[m, i, :] - my_mat[l, j, :])**2).sum() \ for ((m,l),i,j) in \ itertools.product ( itertools.combinations(h,2), range(k), range(k)) ]\ for h in itertools.combinations(range(num_traj), r) ] Apart from being quite unreadable (!!!), it is also taking a long time. Can anyone suggest any ways to improve on this?

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  • SQLAlchemy - select for update example

    - by Mark
    I'm looking for a complete example of using select for update in SQLAlchemy, but haven't found one googling. I need to lock a single row and update a column, the following code doesn't work (blocks forever): s = table.select(table.c.user=="test",for_update=True) u = table.update().where(table.c.user=="test") u.execute(email="foo") Do I need a commit? How do I do that? As far as I know you need to: begin transaction select ... for update update commit

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  • How do I get javascript results using selenium?

    - by Seth
    I have the following code: from selenium import selenium selenium = selenium("localhost", 4444, "*chrome", "http://some_site.com/") selenium.start() sel = selenium sel.open("/") sel.type("ctl00_ContentPlaceHolder1_SuburbTownTextBox", "Adelaide,SA,5000") sel.click("ctl00_ContentPlaceHolder1_SearchImageButton") #text = sel.get_body_text() text = sel.get_html_source() print(text) The click executes a javascript file which then produces results on the same page. Obviously print(text) will only print the orignal html source. How do I get to the results of the javascript?

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  • Error -3 while decompressing data: incorrect header check

    - by Rahul99
    I have .zip file which contain csv data. I am reading .zip file using <input type = "file" name = "select_file"/> I want to decompress that .zip file and read csv data. file_data = self.request.get('select_file') file_str = zlib.decompress(file_data) #file_data_list = file_str.split('\n') #file_Reader = csv.reader(file_data_list,quoting=csv.QUOTE_NONE ) I am expecting csv data in file_str but I am getting error. error :: Error -3 while decompressing data: incorrect header check What I have to use?

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  • Designing a Tag table that tells how many times it's used

    - by Satoru.Logic
    Hi, all. I am trying to design a tagging system with a model like this: Tag: content = CharField creator = ForeignKey used = IntergerField It is a many-to-many relationship between tags and what's been tagged. Everytime I insert a record into the assotication table, Tag.used is incremented by one, and decremented by one in case of deletion. Tag.used is maintained because I want to speed up answering the question 'How many times this tag is used?'. However, this seems to slow insertion down obviously. Please tell me how to improve this design. Thanks in advance.

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  • django newbie question : cant start a new project

    - by Moayyad Yaghi
    hello . I'm totally new to django . and I'm using its documentation to get help on how to use it but seems like something is missing. i installed django using setup.py install command and i added the ( django/bin ) to system path variable but. i still cant start a new project i use the following syntax to start a project : django-admin.py startproject myNewProject but it says Type 'django-admin.py help' for usage. 1 do i miss anything ? thank u

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  • Search a variable for an address

    - by chrissygormley
    Hello, I am trying to match information stored in a variable. I have a list of uuid's and ip addresses beside them. The code I have is: r = re.compile(r'urn:uuid:5EEF382F-JSQ9-3c45-D5E0-K15X8M8K76') m = r.match(str(serv)) if m1: print'Found' The string serv contains is: urn:uuid:7FDS890A-KD9E-3h53-G7E8-BHJSD6789D:[u'http://10.10.10.20:12365/7FDS890A-KD9E-3h53-G7E8-BHJSD6789D/'] --------------------------------------------- urn:uuid:5EEF382F-JSQ9-3c45-D5E0-K15X8M8K76:[u'http://10.10.10.10:42365'] --------------------------------------------- urn:uuid:8DSGF89S-FS90-5c87-K3DF-SDFU890US9:[u'http://10.10.10.40:5234'] --------------------------------------------- So basically I am wanting to find the uuid string and find out what it's address is and store it as a variable. So far I have just tried to get it to match the string to no avail. Can anyone point out a solution to this. Thanks

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  • Why is the destructor called when the CPython garbage collector is disabled?

    - by Frederik
    I'm trying to understand the internals of the CPython garbage collector, specifically when the destructor is called. So far, the behavior is intuitive, but the following case trips me up: Disable the GC. Create an object, then remove a reference to it. The object is destroyed and the __del__ method is called. I thought this would only happen if the garbage collector was enabled. Can someone explain why this happens? Is there a way to defer calling the destructor? import gc import unittest _destroyed = False class MyClass(object): def __del__(self): global _destroyed _destroyed = True class GarbageCollectionTest(unittest.TestCase): def testExplicitGarbageCollection(self): gc.disable() ref = MyClass() ref = None # The next test fails. # The object is automatically destroyed even with the collector turned off. self.assertFalse(_destroyed) gc.collect() self.assertTrue(_destroyed) if __name__=='__main__': unittest.main() Disclaimer: this code is not meant for production -- I've already noted that this is very implementation-specific and does not work on Jython.

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  • How do I call setattr() on the current module?

    - by Matt Joiner
    What do I pass as the first parameter "object" to the function setattr(object, name, value), to set variables on the current module? For example: setattr(object, "SOME_CONSTANT", 42); giving the same effect as: SOME_CONSTANT = 42 within the module containing these lines (with the correct object). I'm generate several values at the module level dynamically, and as I can't define __getattr__ at the module level, this is my fallback.

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  • How to set up Atana Studio 3 Themes in Pydev

    - by willy1234x1
    I've installed the Aptana Studio 3 preview and noticed it has support for themes (such as a bespin style or Ruby envy) and I'd love to use the Bespin one in Pydev but so far I've had no luck getting it to work, anyone have a clue as to how to get it to work? Video showing the themes in action.

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  • Which webserver to use with bottle?

    - by luc
    Bottle can use several webservers: Build-in HTTP development server and support for paste, fapws3, flup, cherrypy or any other WSGI capable server. I am using bottle for a desktop-app and I guess that the development server is enough in this case. I would like to know if some of you have experience with one of the alternative server. Which server for which purpose? Thanks in advance

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  • How can I detect whether an image is a PNG or APNG format?

    - by perlit
    APNG is backwards compatible with PNG. I opened up an apng and png file in a hex editor and the first few bytes look identical. So if a user uploads either of these formats, how do I detect what the format really is? I've seen this done on some sites that block apng. I'm guessing the ImageMagick library makes this easy, but what if I were to do the detect without the use of an image processing library (for learning purposes)? Can I look for specific bytes that tell me if the file is apng? Solutions in any language is welcome.

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  • How to turn a list of tuples into a string?

    - by matt
    I have a list of tuples that I'm trying to incorporate into a SQL query but I can't figure out how to join them together without adding slashes. My like this: list = [('val', 'val'), ('val', 'val'), ('val', 'val')] If I turn each tuple into a string and try to join them with a a comma I'll get something like ' (\'val\, \'val\'), ... ' What's the right way to do this, so I can get the list (without brackets) as a string?

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