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  • SelfReferenceProperty vs. ListProperty Google App Engine

    - by John
    Hi All, I am experimenting with the Google App Engine and have a question. For the sake of simplicity, let's say my app is modeling a computer network (a fairly large corporate network with 10,000 nodes). I am trying to model my Node class as follows: class Node(db.Model): name = db.StringProperty() neighbors = db.SelfReferenceProperty() Let's suppose, for a minute, that I cannot use a ListProperty(). Based on my experiments to date, I can assign only a single entity to 'neighbors' - and I cannot use the "virtual" collection (node_set) to access the list of Node neighbors. So... my questions are: Does SelfReferenceProperty limit you to a single entity that you can reference? If I instead use a ListProperty, I believe I am limited to 5,000 keys, which I need to exceed. Thoughts? Thanks, John

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  • Condition checking vs. Exception handling

    - by Aidas Bendoraitis
    When is exception handling more preferable than condition checking? There are many situations where I can choose using one or the other. For example, this is a summing function which uses a custom exception: # module mylibrary class WrongSummand(Exception): pass def sum_(a, b): """ returns the sum of two summands of the same type """ if type(a) != type(b): raise WrongSummand("given arguments are not of the same type") return a + b # module application using mylibrary from mylibrary import sum_, WrongSummand try: print sum_("A", 5) except WrongSummand: print "wrong arguments" And this is the same function, which avoids using exceptions # module mylibrary def sum_(a, b): """ returns the sum of two summands if they are both of the same type """ if type(a) == type(b): return a + b # module application using mylibrary from mylibrary import sum_ c = sum_("A", 5) if c is not None: print c else: print "wrong arguments" I think that using conditions is always more readable and manageable. Or am I wrong? What are the proper cases for defining APIs which raise exceptions and why?

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  • Is using os.path.abspath to validate an untrusted filename's location secure?

    - by mcmt
    I don't think I'm missing anything. Then again I'm kind of a newbie. def GET(self, filename): name = urllib.unquote(filename) full = path.abspath(path.join(STATIC_PATH, filename)) #Make sure request is not tricksy and tries to get out of #the directory, e.g. filename = "../.ssh/id_rsa". GET OUTTA HERE assert full[:len(STATIC_PATH)] == STATIC_PATH, "bad path" return open(full).read() Edit: I realize this will return the wrong HTTP error code if the file doesn't exist (at least under web.py). I will fix this.

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  • Find subset with K elements that are closest to eachother

    - by Nima
    Given an array of integers size N, how can you efficiently find a subset of size K with elements that are closest to each other? Let the closeness for a subset (x1,x2,x3,..xk) be defined as: 2 <= N <= 10^5 2 <= K <= N constraints: Array may contain duplicates and is not guaranteed to be sorted. My brute force solution is very slow for large N, and it doesn't check if there's more than 1 solution: N = input() K = input() assert 2 <= N <= 10**5 assert 2 <= K <= N a = [] for i in xrange(0, N): a.append(input()) a.sort() minimum = sys.maxint startindex = 0 for i in xrange(0,N-K+1): last = i + K tmp = 0 for j in xrange(i, last): for l in xrange(j+1, last): tmp += abs(a[j]-a[l]) if(tmp > minimum): break if(tmp < minimum): minimum = tmp startindex = i #end index = startindex + K? Examples: N = 7 K = 3 array = [10,100,300,200,1000,20,30] result = [10,20,30] N = 10 K = 4 array = [1,2,3,4,10,20,30,40,100,200] result = [1,2,3,4]

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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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  • How to add a context processor from a Django app

    - by Edan Maor
    Say I'm writing a Django app, and all the templates in the app require a certain variable. The "classic" way to deal with this, afaik, is to write a context processor and add it to TEMPLATE_CONTEXT_PROCESSORS in the settings.py. My question is, is this the right way to do it, considering that apps are supposed to be "independent" from the actual project using them? In other words, when deploying that app to a new project, is there any way to avoid the project having to explicitly mess around with its settings?

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  • How to make scipy.interpolate give a an extrapolated result beyond the input range?

    - by Salim Fadhley
    I'm trying to port a program which uses a hand-rolled interpolator (developed by a mathematitian colleage) over to use the interpolators provided by scipy. I'd like to use or wrap the scipy interpolator so that it has as close as possible behavior to the old interpolator. A key difference between the two functions is that in our original interpolator - if the input value is above or below the input range, our original interpolator will extrapolate the result. If you try this with the scipy interpolator it raises a ValueError. Consider this program as an example: import numpy as np from scipy import interpolate x = np.arange(0,10) y = np.exp(-x/3.0) f = interpolate.interp1d(x, y) print f(9) print f(11) # Causes ValueError, because it's greater than max(x) Is there a sensible way to make it so that instead of crashing, the final line will simply do a linear extrapolate, continuing the gradients defined by the first and last two pouints to infinity. Note, that in the real software I'm not actually using the exp function - that's here for illustration only!

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  • How to create instances of related models in Django

    - by sevennineteen
    I'm working on a CMSy app for which I've implemented a set of models which allow for creation of custom Template instances, made up of a number of Fields and tied to a specific Customer. The end-goal is that one or more templates with a set of custom fields can be defined through the Admin interface and associated to a customer, so that customer can then create content objects in the format prescribed by the template. I seem to have gotten this hooked up such that I can create any number of Template objects, but I'm struggling with how to create instances - actual content objects - in those templates. For example, I can define a template "Basic Page" for customer "Acme" which has the fields "Title" and "Body", but I haven't figured out how to create Basic Page instances where these fields can be filled in. Here are my (somewhat elided) models... class Customer(models.Model): ... class Field(models.Model): ... class Template(models.Model): label = models.CharField(max_length=255) clients = models.ManyToManyField(Customer, blank=True) fields = models.ManyToManyField(Field, blank=True) class ContentObject(models.Model): label = models.CharField(max_length=255) template = models.ForeignKey(Template) author = models.ForeignKey(User) customer = models.ForeignKey(Customer) mod_date = models.DateTimeField('Modified Date', editable=False) def __unicode__(self): return '%s (%s)' % (self.label, self.template) def save(self): self.mod_date = datetime.datetime.now() super(ContentObject, self).save() Thanks in advance for any advice!

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  • Serve external template in Django

    - by AlexeyMK
    Hey, I want to do something like return render_to_response("http://docs.google.com/View?id=bla", args) and serve an external page with django arguments. Django doesn't like this (it looks for templates in very particular places). What's the easiest way make this work? Right now I'm thinking to use urllib to save the page to somewhere locally on my server and then serve with the templates pointing to there. Note: I'm not looking for anything particularly scalable here, I realize my proposal above is a little dirty.

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  • Deterministic key serialization

    - by Mike Boers
    I'm writing a mapping class which uses SQLite as the storage backend. I am currently allowing only basestring keys but it would be nice if I could use a couple more types hopefully up to anything that is hashable (ie. same requirements as the builtin dict). To that end I would like to derive a deterministic serialization scheme. Ideally, I would like to know if any implementation/protocol combination of pickle is deterministic for hashable objects (e.g. can only use cPickle with protocol 0). I noticed that pickle and cPickle do not match: >>> import pickle >>> import cPickle >>> def dumps(x): ... print repr(pickle.dumps(x)) ... print repr(cPickle.dumps(x)) ... >>> dumps(1) 'I1\n.' 'I1\n.' >>> dumps('hello') "S'hello'\np0\n." "S'hello'\np1\n." >>> dumps((1, 2, 'hello')) "(I1\nI2\nS'hello'\np0\ntp1\n." "(I1\nI2\nS'hello'\np1\ntp2\n." Another option is to use repr to dump and ast.literal_eval to load. This would only be valid for builtin hashable types. I have written a function to determine if a given key would survive this process (it is rather conservative on the types it allows): def is_reprable_key(key): return type(key) in (int, str, unicode) or (type(key) == tuple and all( is_reprable_key(x) for x in key)) The question for this method is if repr itself is deterministic for the types that I have allowed here. I believe this would not survive the 2/3 version barrier due to the change in str/unicode literals. This also would not work for integers where 2**32 - 1 < x < 2**64 jumping between 32 and 64 bit platforms. Are there any other conditions (ie. do strings serialize differently under different conditions)? (If this all fails miserably then I can store the hash of the key along with the pickle of both the key and value, then iterate across rows that have a matching hash looking for one that unpickles to the expected key, but that really does complicate a few other things and I would rather not do it.) Any insights?

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  • Generating two thumbnails from the same image in Django

    - by Titus
    Hello, this seems like quite an easy problem but I can't figure out what is going on here. Basically, what I'd like to do is create two different thumbnails from one image on a Django model. What ends up happening is that it seems to be looping and recreating the same image (while appending an underscore to it each time) until it throws up an error that the filename is to big. So, you end up something like: OSError: [Errno 36] File name too long: 'someimg________________etc.jpg' Here is the code: def save(self, *args, **kwargs): if self.image: iname = os.path.split(self.image.name)[-1] fname, ext = os.path.splitext(iname) tlname, tsname = fname + '_thumb_l' + ext, fname + '_thumb_s' + ext self.thumb_large.save(tlname, make_thumb(self.image, size=(250,250))) self.thumb_small.save(tsname, make_thumb(self.image, size=(100,100))) super(Artist, self).save(*args, **kwargs) def make_thumb(infile, size=(100,100)): infile.seek(0) image = Image.open(infile) if image.mode not in ('L', 'RGB'): image.convert('RGB') image.thumbnail(size, Image.ANTIALIAS) temp = StringIO() image.save(temp, 'png') return ContentFile(temp.getvalue()) I didn't show imports for the sake of brevity. Assume there are two ImageFields on the Artist model: thumb_large, and thumb_small. If this isn't the correct way to do it, I'd appreciate any feedback. Thanks!

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  • Unable to control requests for static files on Google App Engine

    - by dan
    My simple GAE app is not redirecting to the /static directory for requests when url is multiple levels. Dir structure: /app/static/css/main.css App: I have two handlers one for /app and one for /app/new app.yaml: handlers: - url: /static static_dir: static - url: /app/static/(.*) static_dir: static\1 - url: /app/.* script: app.py login: required HTML: Description: When page is loaded from /app HTTP request for main.css is successful GET /static/css/main.css But when page is loaded from /app/new I see the following request: GET /app/static/css/main.cs That's when I tried adding the /app/static/(.*) in the app.yaml but it is not having any effect.

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  • initialize a numpy array

    - by Curious2learn
    Is there way to initialize a numpy array of a shape and add to it? I will explain what I need with a list example. If I want to create a list of objects generated in a loop, I can do: a = [] for i in range(5): a.append(i) I want to do something similar with a numpy array. I know about vstack, concatenate etc. However, it seems these require two numpy arrays as inputs. What I need is: big_array # Initially empty. This is where I don't know what to specify for i in range(5): array i of shape = (2,4) created. add to big_array The big_array should have a shape (10,4). How to do this? Thanks for your help.

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  • How small is *too small* for an opensource project?

    - by Adam Lewis
    I have a fair number of smaller projects / libraries that I have been using over the past 2 years. I am thinking about moving them to Google Code to make it easier to share with co-workers and easier to import them into new projects on my own environments. The are things like a simple FSMs, CAN (Controller Area Network) drivers, and GPIB drivers. Most of them are small (less than 500 lines), so it makes me wonder are these types of things too small for a stand alone open-source project? Note that I would like to make it opensource because it does not give me, or my company, any real advantage.

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  • Making all variables accessible to namespace

    - by Gökhan Sever
    Hello, Say I have a simple function: def myfunc(): a = 4.2 b = 5.5 ... many similar variables ... I use this function one time only and I am wondering what is the easiest way to make all the variables inside the function accessible to my main name-space. Do I have to declare global for each item? or any other suggested methods? Thanks.

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  • How can I draw a log-normalized imshow plot with a colorbar representing the raw data in matplotlib

    - by Adam Fraser
    I'm using matplotlib to plot log-normalized images but I would like the original raw image data to be represented in the colorbar rather than the [0-1] interval. I get the feeling there's a more matplotlib'y way of doing this by using some sort of normalization object and not transforming the data beforehand... in any case, there could be negative values in the raw image. import matplotlib.pyplot as plt import numpy as np def log_transform(im): '''returns log(image) scaled to the interval [0,1]''' try: (min, max) = (im[im > 0].min(), im.max()) if (max > min) and (max > 0): return (np.log(im.clip(min, max)) - np.log(min)) / (np.log(max) - np.log(min)) except: pass return im a = np.ones((100,100)) for i in range(100): a[i] = i f = plt.figure() ax = f.add_subplot(111) res = ax.imshow(log_transform(a)) # the colorbar drawn shows [0-1], but I want to see [0-99] cb = f.colorbar(res) I've tried using cb.set_array, but that didn't appear to do anything, and cb.set_clim, but that rescales the colors completely. Thanks in advance for any help :)

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  • Form (or Formset?) to handle multiple table rows in Django

    - by Ben
    Hi, I'm working on my first Django application. In short, what it needs to do is to display a list of film titles, and allow users to give a rating (out of 10) to each film. I've been able to use the {{ form }} and {{ formset }} syntax in a template to produce a form which lets you rate one film at a time, which corresponds to one row in a MySQL table, but how do I produce a form that iterates over all the movie titles in the database and produces a form that lets you rate lots of them at once? At first, I thought this was what formsets were for, but I can't see any way to automatically iterate over the contents of a database table to produce items to go in the form, if you see what I mean. Currently, my views.py has this code: def survey(request): ScoreFormSet = formset_factory(ScoreForm) if request.method == 'POST': formset = ScoreFormSet(request.POST, request.FILES) if formset.is_valid(): return HttpResponseRedirect('/') else: formset = ScoreFormSet() return render_to_response('cf/survey.html', { 'formset':formset, }) And my survey.html has this: <form action="/survey/" method="POST"> <table> {{ formset }} </table> <input type = "submit" value = "Submit"> </form> Oh, and the definition of ScoreForm and Score from models.py are: class Score(models.Model): movie = models.ForeignKey(Movie) score = models.IntegerField() user = models.ForeignKey(User) class ScoreForm(ModelForm): class Meta: model = Score So, in case the above is not clear, what I'm aiming to produce is a form which has one row per movie, and each row shows a title, and has a box to allow the user to enter their score. If anyone can point me at the right sort of approach to this, I'd be most grateful. Thanks, Ben

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  • Scrapy Not Returning Additonal Info from Scraped Link in Item via Request Callback

    - by zoonosis
    Basically the code below scrapes the first 5 items of a table. One of the fields is another href and clicking on that href provides more info which I want to collect and add to the original item. So parse is supposed to pass the semi populated item to parse_next_page which then scrapes the next bit and should return the completed item back to parse Running the code below only returns the info collected in parse If I change the return items to return request I get a completed item with all 3 "things" but I only get 1 of the rows, not all 5. Im sure its something simple, I just can't see it. class ThingSpider(BaseSpider): name = "thing" allowed_domains = ["somepage.com"] start_urls = [ "http://www.somepage.com" ] def parse(self, response): hxs = HtmlXPathSelector(response) items = [] for x in range (1,6): item = ScrapyItem() str_selector = '//tr[@name="row{0}"]'.format(x) item['thing1'] = hxs.select(str_selector")]/a/text()').extract() item['thing2'] = hxs.select(str_selector")]/a/@href').extract() print 'hello' request = Request("www.nextpage.com", callback=self.parse_next_page,meta={'item':item}) print 'hello2' request.meta['item'] = item items.append(item) return items def parse_next_page(self, response): print 'stuff' hxs = HtmlXPathSelector(response) item = response.meta['item'] item['thing3'] = hxs.select('//div/ul/li[1]/span[2]/text()').extract() return item

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  • How to allow resizing of QMessageBox in PyQt4

    - by Simeon Fitch
    I'm using the nice feature in QMessageBox to optionally show detailed text to the user. However, the window after expansion is still fairly small, and one immediately tries to resize the window so more of the details are visible. Even after setting what I think are the proper settings it won't allow resizing. Here's the relevant snippet of PyQt4 code: mb = QMessageBox() mb.setText("Results written to '%s'" % filename) mb.setDetailedText(str(myData)) mb.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Expanding) mb.setSizeGripEnabled(True) Am I missing a step and/or is this at all possible?

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  • How to get bit rotation function to accept any bit size?

    - by calccrypto
    i have these 2 functions i got from some other code def ROR(x, n): mask = (2L**n) - 1 mask_bits = x & mask return (x >> n) | (mask_bits << (32 - n)) def ROL(x, n): return ROR(x, 32 - n) and i wanted to use them in a program, where 16 bit rotations are required. however, there are also other functions that require 32 bit rotations, so i wanted to leave the 32 in the equation, so i got: def ROR(x, n, bits = 32): mask = (2L**n) - 1 mask_bits = x & mask return (x >> n) | (mask_bits << (bits - n)) def ROL(x, n, bits = 32): return ROR(x, bits - n) however, the answers came out wrong when i tested this set out. yet, the values came out correctly when the code is def ROR(x, n): mask = (2L**n) - 1 mask_bits = x & mask return (x >> n) | (mask_bits << (16 - n)) def ROL(x, n,bits): return ROR(x, 16 - n) what is going on and how do i fix this?

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  • twisted reactor stops too early

    - by pygabriel
    I'm doing a batch script to connect to a tcp server and then exiting. My problem is that I can't stop the reactor, for example: cmd = raw_input("Command: ") # custom factory, the protocol just send a line reactor.connectTCP(HOST,PORT, CommandClientFactory(cmd) d = defer.Deferred() d.addCallback(lambda x: reactor.stop()) reactor.callWhenRunning(d.callback,None) reactor.run() In this code the reactor stops before that the tcp connection is done and the cmd is passed. How can I stop the reactor after that all the operation are finished?

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