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  • What is the proper way to check the previous value of a field before saving an object? (Using Django

    - by anonymous coward
    I have a Django Model with updated_by and an approved_by fields, both are ForeignKey fields to the built-in (auth) User models. I am aware that with updated_by, it's easy enough to simply over-ride the .save() method on the Model, and shove the request.user in that field before saving. However, for approved_by, this field should only ever be filled in when a related field (date_approved) is first filled in. I'm somewhat certain that I can check this logically, and fill in the field if the previous value was empty. What is the proper way to check the previous value of a field before saving an object? I do not anticipate that date_approved will ever be changed or updated, nor should there be any reason to ever update the approved_by entry. UPDATE: Regarding forms/validation, I should have mentioned that none of the fields in question are seen by or editable by users of the site. If I have misunderstood, I'm sorry, but I'm not sure how forms and validation apply to my question.

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  • Iterating over a database column in Django

    - by curious
    I would like to iterate a calculation over a column of values in a MySQL database. I wondered if Django had any built-in functionality for doing this. Previously, I have just used the following to store each column as a list of tuples with the name table_column: import MySQLdb import sys try: conn = MySQLdb.connect (host = "localhost", user = "user", passwd="passwd", db="db") except MySQLdb.Error, e: print "Error %d: %s" % (e.args[0], e.args[1]) sys.exit (1) cursor = conn.cursor() for table in ['foo', 'bar']: for column in ['foobar1', 'foobar2']: cursor.execute('select %s from %s' % (column, table)) exec "%s_%s = cursor.fetchall()" % (table, column) cursor.close() conn.commit() conn.close() Is there any functionality built into Django to more conveniently iterate through the values of a column in a database table? I'm dealing with millions of rows so speed of execution is important.

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  • Aggregation over a few models - Django

    - by RadiantHex
    Hi folks, I'm trying to compute the average of a field over various subsets of a queryset. Player.objects.order_by('-score').filter(sex='male').aggregate(Avg('level')) This works perfectly! But... if I try to compute it for the top 50 players it does not work. Player.objects.order_by('-score').filter(sex='male')[:50].aggregate(Avg('level')) This last one returns the exact same result as the query above it, which is wrong. What am I doing wrong? Help would be very much appreciated!

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  • How to attach a line to a moving object?

    - by snow-spur
    Hello i have designed a maze and i want to draw a path between the cells as the 'person' moves from one cell to the next. So each time i move the cell a line is drawn I have done this so far but do not want to show my full code However i get an error saying Circle has no attribute center my circle which is my cell center = Point(15, 15) c = Circle(center, 12) c.setFill('blue') c.setOutline('yellow') c.draw(win) p1 = Point(c.center().getx(), c.center().gety()) this bit is in my loop p2 = Point(getx(), gety()) line = graphics.Line(p1, p2)

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  • I need to change a zip code into a series of dots and dashes (a barcode), but I can't figure out how

    - by Maggie
    Here's what I've got so far: def encodeFive(zip): zero = "||:::" one = ":::||" two = "::|:|" three = "::||:" four = ":|::|" five = ":|:|:" six = ":||::" seven = "|:::|" eight = "|::|:" nine = "|:|::" codeList = [zero,one,two,three,four,five,six,seven,eight,nine] allCodes = zero+one+two+three+four+five+six+seven+eight+nine code = "" digits = str(zip) for i in digits: code = code + i return code With this I'll get the original zip code in a string, but none of the numbers are encoded into the barcode. I've figured out how to encode one number, but it wont work the same way with five numbers.

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  • maching strings

    - by kiran
    Write two functions, called countSubStringMatch and countSubStringMatchRecursive that take two arguments, a key string and a target string. These functions iteratively and recursively count the number of instances of the key in the target string. You should complete definitions for def countSubStringMatch(target,key): and def countSubStringMatchRecursive (target, key): For the remaining problems, we are going to explore other substring matching ideas. These problems can be solved with either an iterative function or a recursive one. You are welcome to use either approach, though you may find iterative approaches more intuitive in these cases of matching linear structures.

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  • Web and stand-alone apps development tendency

    - by Narek
    There is a strong tendency of making web apps and even seems that very soon a lot of features will be available online so that for every day use people will have all necessary software free online and they will not need to install any software locally. Only specific (professional) tools that usually people don’t use at home will not be available as a web app. So my question, how do you imagine selling software that was necessary for everyday use and was not free (seems they can't make money any more by selling their product – no need of those products). And what disadvantages have web apps, that is to say, what is bad to use software online compared with having the same software locally (please list)? Please do not consider this question not connected with programming, as I really would like to have a little statistics from professional programmers who are aware from nowday’s tendency of software and programming. Thanks.

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  • What do I do with a Concrete Syntax Tree?

    - by Cap
    I'm using pyPEG to create a parse tree for a simple grammar. The tree is represented using lists and tuples. Here's an example: [('command', [('directives', [('directive', [('name', 'retrieve')]), ('directive', [('name', 'commit')])]), ('filename', [('name', 'f30502')])])] My question is what do I do with it at this point? I know a lot depends on what I am trying to do, but I haven't been able to find much about consuming/using parse trees, only creating them. Does anyone have any pointers to references I might use? Thanks for your help.

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  • Can I override a query in DJango?

    - by stinkypyper
    I know you can override delete and save methods in DJango models, but can you override a select query somehow to intercept and change a parameter slightly. I have a hashed value I want to check for, and would like to keep the hashing internal to the model.

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  • Save JSON outputed from a URL to a file

    - by Aidan
    Hey Guys, How would I save JSON outputed by an URL to a file? e.g from the Twitter search API (this http://search.twitter.com/search.json?q=hi) Language isn't important. Thanks! edit // How would I then append further updates to EOF?

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  • muti user dungeon help

    - by mudman
    ive created a single user dungeon which i would like to create into a multi user dungoen so at least two plays can play how would i do that what code do i need to add can anyone help? i would show coding but if i do then everyone would see it and all my work will be copied as i know other students do use this site to so plz understand my situation and yes this is a homework/assignment work.

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  • Django & custom auth backend (web service) + no database. How to save stuff in session?

    - by Infinity
    I've been searching here and there, and based on this answer I've put together what you see below. It works, but I need to put some stuff in the user's session, right there inside authenticate. How would I store acme_token in the user's session, so that it will get cleared if they logged out? class AcmeUserBackend(object): # Create a User object if not already in the database? create_unknown_user = False def get_user(self, username): return AcmeUser(id=username) def authenticate(self, username=None, password=None): """ Check the username/password and return an AcmeUser. """ acme_token = ask_another_site_about_creds(username, password) if acme_token: return AcmeUser(id=username) return None ################## from django.contrib.auth.models import User class AcmeUser(User): objects = None # we cannot really use this w/o local DB def save(self): """saving to DB disabled""" pass def get_group_permissions(self): """If you don't make your own permissions module, the default also will use the DB. Throw it away""" return [] # likewise with the other permission defs def get_and_delete_messages(self): """Messages are stored in the DB. Darn!""" return []

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  • Returning all "positions" of a list

    - by Daymor
    I Have a list with "a" and "b" and the "b"'s are somewhat of a path and "a"'s are walls. Im writing a program to make a graph of all the possible moves. I got the code running to check the first "b" for possible moves, but i have NO Idea how im going to find all "b"'s , even less check them all without repeating. Major issue im having is getting the tuple coordinates of the "b"'s out of the list. Any pointers/tips?

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  • Increment number in string

    - by iform
    Hi, I am stumped... I am trying to get the following output until a certain condition is met. test_1.jpg test_2.jpg .. test_50.jpg The solution (if you could remotely call it that) that I have is fileCount = 0 while (os.path.exists(dstPath)): fileCount += 1 parts = os.path.splitext(dstPath) dstPath = "%s_%d%s" % (parts[0], fileCount, parts[1]) however...this produces the following output. test_1.jpg test_1_2.jpg test_1_2_3.jpg .....etc The Question: How do I get change the number in its current place (without appending numbers to the end)? Ps. I'm using this for a file renaming tool.

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  • How to merge or copy anonymous session data into user data when user logs in?

    - by benhoyt
    This is a general question, or perhaps a request for pointers to other open source projects to look at: I'm wondering how people merge an anonymous user's session data into the authenticated user data when a user logs in. For example, someone is browsing around your websites saving various items as favourites. He's not logged in, so they're saved to an anonymous user's data. Then he logs in, and we need to merge all that data into their (possibly existing) user data. Is this done different ways in an ad-hoc fashion for different applications? Or are there some best practices or other projects people can direct me to?

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  • Creating temporary user accounts - Django

    - by RadiantHex
    Hi folks, I need to setup temporary User models for each visitors, where the visitors are obviously tied by session data. I might not be aware of it, but does Django support attaching data to Anonymous users? The only way, I am currently aware of, is to use the session dictionary part of the request object. Help would be very much appreciated!

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  • Why is numpy c extension slow?

    - by Bitwise
    I am working on large numpy arrays, and some native numpy operations are too slow for my needs (for example simple operations such as "bitwise" A&B). I started looking into writing C extensions to try and improve performance. As a test case, I tried the example given here, implementing a simple trace calculation. I was able to get it to work, but was surprised by the performance: for a (1000,1000) numpy array, numpy.trace() was about 1000 times faster than the C extension! This happens whether I run it once or many times. Is this expected? Is the C extension overhead that bad? Any ideas how to speed things up?

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