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  • How can I implement "real time" messaging on Google AppEngine?

    - by Freed
    I'm creating a web application on Google AppEngine where I want the user to be notified a quickly as possible after certain events occour. The problem is similar to say a chat server in that I need something happening on one connection (someone is writing a message in a chat room) to propagate to a number of other connections (other people in that chat room gets the message). To get speedy updates from the server to the client I'm planning on using long polling with XmlHttpRequest, hoping that AppEngine won't interfere other than possibly restriing the timeout. The real problem however is efficient notification between connections on AppEngine. Is there any support for this type of cross connection notification on AppEngine that does not involve busy-waiting? The only tools I can think of to do this at all is either using the data storage (slow) or memcache (unreliable), and none of them would let me avoid busy-waiting. Note: I know about XMPP support on AppEngine. It's related, but I want a browser based solution, sending messages to the users by XMPP is not an option.

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  • Use a foreign key mapping to get data from the other table using Python and SQLAlchemy.

    - by Az
    Hmm, the title was harder to formulate than I thought. Basically, I've got these simple classes mapped to tables, using SQLAlchemy. I know they're missing a few items but those aren't essential for highlighting the problem. class Customer(object): def __init__(self, uid, name, email): self.uid = uid self.name = name self.email = email def __repr__(self): return str(self) def __str__(self): return "Cust: %s, Name: %s (Email: %s)" %(self.uid, self.name, self.email) The above is basically a simple customer with an id, name and an email address. class Order(object): def __init__(self, item_id, item_name, customer): self.item_id = item_id self.item_name = item_name self.customer = None def __repr__(self): return str(self) def __str__(self): return "Item ID %s: %s, has been ordered by customer no. %s" %(self.item_id, self.item_name, self.customer) This is the Orders class that just holds the order information: an id, a name and a reference to a customer. It's initialised to None to indicate that this item doesn't have a customer yet. The code's job will assign the item a customer. The following code maps these classes to respective database tables. # SQLAlchemy database transmutation engine = create_engine('sqlite:///:memory:', echo=False) metadata = MetaData() customers_table = Table('customers', metadata, Column('uid', Integer, primary_key=True), Column('name', String), Column('email', String) ) orders_table = Table('orders', metadata, Column('item_id', Integer, primary_key=True), Column('item_name', String), Column('customer', Integer, ForeignKey('customers.uid')) ) metadata.create_all(engine) mapper(Customer, customers_table) mapper(Orders, orders_table) Now if I do something like: for order in session.query(Order): print order I can get a list of orders in this form: Item ID 1001: MX4000 Laser Mouse, has been ordered by customer no. 12 What I want to do is find out customer 12's name and email address (which is why I used the ForeignKey into the Customer table). How would I go about it?

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  • What is the best way to do Bit Field manipulation in Python?

    - by ZebZiggle
    I'm reading some MPEG Transport Stream protocol over UDP and it has some funky bitfields in it (length 13 for example). I'm using the "struct" library to do the broad unpacking, but is there a simple way to say "Grab the next 13 bits" rather than have to hand-tweak the bit manipulation? I'd like something like the way C does bit fields (without having to revert to C). Suggestions?

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  • how to diff / align Python lists using arbitrary matching function?

    - by James Tauber
    I'd like to align two lists in a similar way to what difflib.Differ would do except I want to be able to define a match function for comparing items, not just use string equality, and preferably a match function that can return a number between 0.0 and 1.0, not just a boolean. So, for example, say I had the two lists: L1 = [('A', 1), ('B', 3), ('C', 7)] L2 = ['A', 'b', 'C'] and I want to be able to write a match function like this: def match(item1, item2): if item1[0] == item2: return 1.0 elif item1[0].lower() == item2.lower(): return 0.5 else: return 0 and then do: d = Differ(match_func=match) d.compare(L1, L2) and have it diff using the match function. Like difflib, I'd rather the algorithm gave more intuitive Ratcliff-Obershelp type results rather than a purely minimal Levenshtein distance.

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  • How to insert and call by row and column into sqlite3 python, great tutorial problem.

    - by user291071
    Lets say i have a simple array of x rows and y columns with corresponding values, What is the best method to do 3 things? How to insert, update a value at a specific row column? How to select a value for each row and column, import sqlite3 con = sqlite3.connect('simple.db') c = con.cursor() c.execute('''create table simple (links text)''') con.commit() dic = {'x1':{'y1':1.0,'y2':0.0},'x2':{'y1':0.0,'y2':2.0,'y3':1.5},'x3':{'y2':2.0,'y3':1.5}} ucols = {} ## my current thoughts are collect all row values and all column values from dic and populate table row and columns accordingly how to call by row and column i havn't figured out yet ##populate rows in first column for row in dic: print row c.execute("""insert into simple ('links') values ('%s')"""%row) con.commit() ##unique columns for row in dic: print row for col in dic[row]: print col ucols[col]=dic[row][col] ##populate columns for col in ucols: print col c.execute("alter table simple add column '%s' 'float'" % col) con.commit() #functions needed ##insert values into sql by row x and column y?how to do this e.g. x1 and y2 should put in 0.0 ##I tried as follows didn't work for row in dic: for col in dic[row]: val =dic[row][col] c.execute("""update simple SET '%s' = '%f' WHERE 'links'='%s'"""%(col,val,row)) con.commit() ##update value at a specific row x and column y? ## select a value at a specific row x and column y?

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  • Python: When passing variables between methods, is it necessary to assign it a new name?

    - by Anthony
    I'm thinking that the answer is probably 'no' if the program is small and there are a lot of methods, but what about in a larger program? If I am going to be using one variable in multiple methods throughout the program, is it smarter to: Come up with a different phrasing for each method (to eliminate naming conflicts). Use the same name for each method (to eliminate confusion) Just use a global variable (to eliminate both) This is more of a stylistic question than anything else. What naming convention do YOU use when passing variables?

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  • Rapid spectral analysis of audio file using Python 2.6?

    - by Ephemeralis
    What I want to do is to have a subroutine that analyses every 200 milliseconds of a sound file which it is given and spits out the frequency intensity value (from 0 to 1 as a float) of a specific frequency range into an array which I later save. This value then goes on to be used as the opacity value for a graphic which is supposed to 'strobe' to the audio file. The problem is, I have never ventured into audio analysis before and have no clue where to start. I have looked pymedia and scipy/numpy thinking I would be able to use FFT in order to achieve this, but I am not really sure how I would manipulate this data to end up with the desired result. The documentation on the SpectrAnalyzer class of pymedia is virtually non-existant and the examples on the website do not actually work with the latest release of the library - which isn't exactly making my life easier. How would I go about starting this project? I am at a complete loss as to what libraries I should even be using.

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  • How can I login to a website with Python?

    - by Shady
    How can I do it? I was trying to enter some specified link (with urllib), but to do it, I need to log in. I have this source from the site: <form id="login-form" action="auth/login" method="post"> <div> <!--label for="rememberme">Remember me</label><input type="checkbox" class="remember" checked="checked" name="remember me" /--> <label for="email" id="email-label" class="no-js">Email</label> <input id="email-email" type="text" name="handle" value="" autocomplete="off" /> <label for="combination" id="combo-label" class="no-js">Combination</label> <input id="password-clear" type="text" value="Combination" autocomplete="off" /> <input id="password-password" type="password" name="password" value="" autocomplete="off" /> <input id="sumbitLogin" class="signin" type="submit" value="Sign In" /> Is this possible?

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  • Should I be using abstract methods in this Python scenario?

    - by sfjedi
    I'm not sure my approach is good design and I'm hoping I can get a tip. I'm thinking somewhere along the lines of an abstract method, but in this case I want the method to be optional. This is how I'm doing it now... from pymel.core import * class A(object): def __init__(self, *args, **kwargs): if callable(self.createDrivers): self._drivers = self.createDrivers(*args, **kwargs) select(self._drivers) class B(A): def createDrivers(self, *args, **kwargs): c1 = circle(sweep=270)[0] c2 = circle(sweep=180)[0] return c1, c2 b = B() In the above example, I'm just creating 2 circle arcs in PyMEL for Maya, but I fully intend on creating more subclasses that may or may not have a createDrivers method at all! So I want it to be optional and I'm wondering if my approach is—well, if my approach could be improved?

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  • Elegent way to collapse or expand sub-sequences of a list in Python?

    - by forgot
    I want to collapse or expand sub-sequences of a list e.g. ['A', 'B', 'D', 'E', 'H'] -> ['AB', 'DE', 'H'] and vice versa currently I wrote some ugly code like: while True: for i, x in enumerate(s): if x == 'A' and s[i+1] == 'B': s[i:i+2] = 'AB' break else: break For people who asking 'why do that thing': Actually I'm working on a optimizing compiler and this is the peephole part. Writing pattern matching is a little annoying.

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  • Python library to detect if a file has changed between different runs?

    - by Stefano Borini
    Suppose I have a program A. I run it, and performs some operation starting from a file foo.txt. Now A terminates. New run of A. It checks if the file foo.txt has changed. If the file has changed, A runs its operation again, otherwise, it quits. Does a library function/external library for this exists ? Of course it can be implemented with an md5 + a file/db containing the md5. I want to prevent reinventing the wheel.

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  • What's the non brute force way to filter a Python dictionary?

    - by Thierry Lam
    I can filter the following dictionary like: data = { 1: {'name': 'stackoverflow', 'traffic': 'high'}, 2: {'name': 'serverfault', 'traffic': 'low'}, 3: {'name': 'superuser', 'traffic': 'low'}, 4: {'name': 'mathoverflow', 'traffic': 'low'}, } traffic = 'low' for k, v in data.items(): if v['traffic'] == traffic: print k, v Is there an alternate way to do the above filtering?

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  • Can a python view template be made to be 'safe/secure' if I make it user editable?

    - by Blankman
    Say I need to have a templating system where a user can edit it online using an online editor. So they can put if tags, looping tags etc., but ONLY for specific objects that I want to inject into the template. Can this be made to be safe from security issues? i.e. them somehow outputing sql connection string information or scripting things outside of the allowable tags and injected objects.

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  • Python Logging across multiple classes and files; how to configure so as to be easily disabled?

    - by mellort
    Currently, I have osmething like this in all of my classes: # Import logging to log information import logging # Set up the logger LOG_FILENAME = 'log.txt' logging.basicConfig(filename=LOG_FILENAME,level=logging.DEBUG) This works well, and I get the output I want, but I would really like to have all this sort of information in one place, and be able to just do something like import myLogger and then start logging, and then hopefully be able to just go into that file and turn off logging when I need an extra performance boost. Thanks in advance

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  • Python: How to extract xml embedded in a html file?

    - by georgehu
    I have a html file with xml snipped embedded, the source code is pasted in the pastbin: http://pastebin.com/Hy0QaWk8 my task is to extract the text enclosed in the first textarea, which is a xml snippet, from the html. Without any change to the original snippet. I'm able to get it by using the BeautifulSoup, but it changes all the tag names into lower case.

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