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• Is recursion ever faster than looping?

  - by Carson Myers

  I know that recursion is sometimes a lot cleaner than looping, and I'm not asking anything about when I should use recursion over iteration, I know there are lots of questions about that already. What I'm asking is, is recursion ever faster than a loop? To me it seems like, you would always be able to refine a loop and get it to perform more quickly than a recursive function because the loop is absent constantly setting up new stack frames. I'm specifically looking for whether recursion is faster in applications where recursion is the right way to handle the data, such as in some sorting functions, in binary trees, etc.

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• Why use a whitelist for HTML sanitizing?

  - by Carson Myers

  I've often wondered -- why use a whitelist as opposed to a blacklist when sanitizing HTML input? How many sneaky HTML tricks are there to open XSS vulnerabilities? Obviously script tags and frames are not allowed, and a whitelist would be used on the fields in HTML elements, but why disallow most of everything?

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• Best way to parse RSS/Atom feeds with PHP

  - by carson

  I'm currently using Magpie RSS but it sometimes falls over when the RSS or Atom feed isn't well formed. Are there any other options for parsing RSS and Atom feeds with PHP?

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• How do I make this simple list comprehension?

  - by Carson Myers

  I'm new to python, and I'm trying to get to know the list comprehensions better. I'm not even really sure if list comprehension is the word I'm looking for, since I'm not generating a list. But I am doing something similar. This is what I am trying to do: I have a list of numbers, the length of which is divisible by three. So say I have nums = [1, 2, 3, 4, 5, 6] I want to iterate over the list and get the sum of each group of three digits. Currently I am doing this: for i in range(0, len(nums), 3): nsum = a + b + c for a, b, c in nums[i, i+3] print(nsum) I know this is wrong, but is there a way to do this? I'm sure I've overlooked something probably very simple... But I can't think of another way to do this.

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• How should I implement reverse AJAX in a Django application?

  - by Carson Myers

  How should I implement reverse AJAX when building a chat application in Django? I've looked at Django-Orbited, and from my understanding, this puts a comet server in front of the HTTP server. This seems fine if I'm just running the Django development server, but how does this work when I start running the application from mod_wsgi? How does having the orbited server handling every request scale? Is this the correct approach? I've looked at another approach (long polling) that seems like it would work, although I'm not sure what all would be involved. Would the client request a page that would live in its own thread, so as not to block the rest of the application? Would it even block? Wouldn't the script requested by the client have to continuously poll for information? Which of the approaches is more proper? Which is more portable, scalable, sane, etc? Are there other good approaches to this (aside from the client polling for messages) that I have overlooked?

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• How can I create my own form designer?

  - by Carson Myers

  I'm starting my first C# project, and I want to make a "form designer" (like the one in VS). The idea is, there will be a visual form designer with a limited toolbox, which will generate Python code (later more) to create the same form. Problem is, I have no idea how to even get started. First of all, I have the form designer in VS: how do I make a "form-within-a-form?" Next... I have no idea how complicated this is going to be. I suppose I could just make little boxes appear beside each control created on the form when it is clicked, for resizing, and make a textbox appear on it when double clicked or something, to change the text in it... Things like this. So another thing I would like to know is this: I do have programming experience in C and C++, I've done PHP for a number of years and am starting with Python as of recently. I've generated forms dynamically in VB6. Given this experience, am I in way over my head with this project?

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• import problem with twisted.web server

  - by Carson Myers

  I'm just getting started with twisted.web, and I'm having trouble importing a Python module into a .rpy script. in C:\py\twisted\mysite.py, I have this: from twisted.web.resource import Resource from twisted.web import server class MySite(Resource): def render_GET(self, request): request.write("<!DOCTYPE html>") request.write("<html><head>") request.write("<title>Twisted Driven Site</title>") request.write("</head><body>") request.write("<h1>Twisted Driven Website</h1>") request.write("<p>Prepath: <pre>{0}</pre></p>".format(request.prepath)) request.write("</body></html>") request.finish() return server.NOT_DONE_YET and in C:\py\twisted\index.rpy, I have this: import mysite reload(mysite) resource = mysite.MySite() I ran twistd -n web --port 8888 --path C:\py\twisted in command prompt and the server started successfully. But when I requested localhost:8888 I got a (huge) stack trace originating from an ImportError: <type 'exceptions.ImportError'>: No module named mysite I can import the module from the interpreter, and if i just execute index.rpy as a python script, I don't get the import error. The documentation on this subject is a bit vague, it just says "However, it is often a better idea to define Resource subclasses in Python modules. In order for changes in modules to be visible, you must either restart the Python process, or reload the module:" (from here). Does anyone know the proper way to do this?

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• how to define current timestamp in yaml with doctrine

  - by Carson

  I tried the following yaml code: columns: created_time: type: timestamp notnull: true default: default CURRENT_TIMESTAMP In the outputted sql statement, the field is treated as datetime instead of timestamp, which I cannot define the current timestamp in it... If I insist to use timestamp to store current time, how to do so in yaml?

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• Is there a GUI framework that uses HTML and CSS to build GUIs?

  - by Carson Myers

  I mean, other than a browser, of course -- I'm talking about building native applications with HTML and CSS -- not web applications, but real native GUIs. I wonder if such a thing exists? And what do you think of such a beast? What would the pros/cons of such a system be?

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• svnserve.conf authentication not worked

  - by Carson

  I can setup Subversion server. I can commit change. The only thing I am not sure is to set up the basic authentication with svnserve. Here is the tutorial I followed: http://tortoisesvn.net/docs/release/TortoiseSVN_en/tsvn-serversetup-svnserve.html#tsvn-serversetup-svnserve-4 Based on the tutorial, I edited the 2 files: svnserve.conf and passwd, and restarted the apache server. But the authentication still cannot work. Even if I set: anon-access = none and restart apache, I can still read svn files and commit change from Eclipse. Have I missed any steps?

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• how do simple SQLAlchemy relationships work?

  - by Carson Myers

  I'm no database expert -- I just know the basics, really. I've picked up SQLAlchemy for a small project, and I'm using the declarative base configuration rather than the "normal" way. This way seems a lot simpler. However, while setting up my database schema, I realized I don't understand some database relationship concepts. If I had a many-to-one relationship before, for example, articles by authors (where each article could be written by only a single author), I would put an author_id field in my articles column. But SQLAlchemy has this ForeignKey object, and a relationship function with a backref kwarg, and I have no idea what any of it MEANS. I'm scared to find out what a many-to-many relationship with an intermediate table looks like (when I need additional data about each relationship). Can someone demystify this for me? Right now I'm setting up to allow openID auth for my application. So I've got this: from __init__ import Base from sqlalchemy.schema import Column from sqlalchemy.types import Integer, String class Users(Base): __tablename__ = 'users' id = Column(Integer, primary_key=True) username = Column(String, unique=True) email = Column(String) password = Column(String) salt = Column(String) class OpenID(Base): __tablename__ = 'openid' url = Column(String, primary_key=True) user_id = #? I think the ? should be replaced by Column(Integer, ForeignKey('users.id')), but I'm not sure -- and do I need to put openids = relationship("OpenID", backref="users") in the Users class? Why? What does it do? What is a backref?

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• How to order the items in a nested LINQ-provided collection

  - by Carson McComas

  I've got a (SQL Server) database table called Category. And another database table called SubCategory. SubCategory has a foreign key relationship to Category. Because of this, thanks to LINQ, each Cateogory has a property called SubCategories and LINQ is nice enough to return all the SubCategories associated with my Category when I grab it. If I want to sort the Categories alphabetically, I can just do: return db.Categories.OrderBy(c => c.Name); However, I have no idea how to order the SubCategories collection inside each Category. My goal is to return a collection of Categories, where all of the SubCategory collections inside of them are ordered alphabetically by Name.

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• Haskell Cons Operator (:)

  - by Carson Myers

  I am really new to Haskell (Actually I saw "Real World Haskell" from O'Reilly and thought "hmm, I think I'll learn functional programming" yesterday) and I am wondering: I can use the construct operator to add an item to the beginning of a list: 1 : [2,3] [1,2,3] I tried making an example data type I found in the book and then playing with it: --in a file data BillingInfo = CreditCard Int String String | CashOnDelivery | Invoice Int deriving (Show) --in ghci $ let order_list = [Invoice 2345] $ order_list [Invoice 2345] $ let order_list = CashOnDelivery : order_list $ order_list [CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, ...- etc... it just repeats forever, is this because it uses lazy evaluation? -- EDIT -- okay, so it is being pounded into my head that let order_list = CashOnDelivery:order_list doesn't add CashOnDelivery to the original order_list and then set the result to order_list, but instead is recursive and creates an infinite list, forever adding CashOnDelivery to the beginning of itself. Of course now I remember that Haskell is a functional language and I can't change the value of the original order_list, so what should I do for a simple "tack this on to the end (or beginning, whatever) of this list?" Make a function which takes a list and BillingInfo as arguments, and then return a list? -- EDIT 2 -- well, based on all the answers I'm getting and the lack of being able to pass an object by reference and mutate variables (such as I'm used to)... I think that I have just asked this question prematurely and that I really need to delve further into the functional paradigm before I can expect to really understand the answers to my questions... I guess what i was looking for was how to write a function or something, taking a list and an item, and returning a list under the same name so the function could be called more than once, without changing the name every time (as if it was actually a program which would add actual orders to an order list, and the user wouldn't have to think of a new name for the list each time, but rather append an item to the same list).

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• How can I create a simple message box in Python?

  - by Carson Myers

  I'm looking for the same effect as alert() in JavaScript. I wrote a simple web-based interpreter this afternoon using Twisted.web. You basically submit a block of Python code through a form, and the client comes and grabs it and executes it. I want to be able to make a simple popup message, without having to re-write a whole bunch of boilerplate wxPython or TkInter code every time (since the code gets submitted through a form and then disappears). I've tried tkMessageBox: import tkMessageBox tkMessageBox.showinfo(title="Greetings", message="Hello World!") but this opens another window in the background with a tk icon. I don't want this. I was looking for some simple wxPython code but it always required setting up a class and entering an app loop etc. Is there no simple, catch-free way of making a message box in Python?

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• which is better, creating a materialized view or a new table?

  - by Carson

  I have some demanding mysql queries that are needed to grap same up-to-date datasets from 5-7 mysql tables. I am thinking of creating a table or materialized view to gather all demanding columns from other tables, so as to increase performance. If I create that table, I may need to do extra insert / update / delete operation each time other tables updated. if I create materialized view, I am worrying if the performance can be greatly improved. Because data from other tables are changing very frequently. Most likely, the view may need to be created first everytime before selecting it. Any ideas? e.g. how to cache? other extra measures I can do?

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• How do I handle the messages for a simple web-based live chat, on the server side?

  - by Carson Myers

  I'm building a simple live chat into a web application running on Django, but one thing I'm confused about is how I should store the messages between users. The chat will support multiple users, and a chat "session" is composed of users connected to one user that is the "host." The application is a sort of online document collaboration thing, so user X has a document, and users Y and Z would connect to user X to talk about the document, and that would be one chat session. If user Y disconnected for five minutes, and then signed back in and reconnected to user X, he should not get any of the messages shared between users X and Z while he was away. if users X, Y, and Z can have a chat session about user X's document, then users X and Y can connect to a simultaneous, but separate discussion about user Z's document. How should I handle this? Should I keep each message in the database? Each message would have an owner user and a target user (the host), and a separate table would be used to connect users with messages (which messages are visible to what users). Or should I store each session as an HTML file on the server, which messages get appended to? The problem is, I can't just send messages directly between clients. They have to be sent to the server in a POST request, and then each client has to periodically check for the messages in a GET request. Except I can't just have each message cleared after a client fetches it, because there could be multiple clients. How should I set this up? Any suggestions?

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• accessing private variable from member function in PHP

  - by Carson Myers

  I have derived a class from Exception, basically like so: class MyException extends Exception { private $_type; public function type() { return $this->_type; //line 74 } public function __toString() { include "sometemplate.php"; return ""; } } Then, I derived from MyException like so: class SpecialException extends MyException { private $_type = "superspecial"; } If I throw new SpecialException("bla") from a function, catch it, and go echo $e, then the __toString function should load a template, display that, and then not actually return anything to echo. This is basically what's in the template file <div class="<?php echo $this->type(); ?>class"> <p> <?php echo $this->message; ?> </p> </div> in my mind, this should definitely work. However, I get the following error when an exception is thrown and I try to display it: Fatal error: Cannot access private property SpecialException::$_type in C:\path\to\exceptions.php on line 74 Can anyone explain why I am breaking the rules here? Am I doing something horribly witty with this code? Is there a much more idiomatic way to handle this situation? The point of the $_type variable is (as shown) that I want a different div class to be used depending on the type of exception caught.

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• how is the definition of 'Commit...', 'Apply Patch' and 'Share Project' in Eclipse for SVN?

  - by Carson

  Everytime before connecting to svn server, there are 2 'Team' options to choose: 'Apply Patch' and 'Share Project'. Both options seem to perform the same when intializing the svn project. In addition, how is the functional difference between 'Commit...' and 'Apply Patch'? What exactly is the difference?

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• associating a filetype with a batch script, and getting parameters passed to file of that type.

  - by Carson Myers

  Sorry for the cryptic title. I have associated python scripts with a batch file that looks like this: python %* I did this because on my machine, python is installed at C:\python26 and I prefer not to reinstall it (for some reason, it won't let me add a file association to the python interpreter. I can copy the executable to Program Files and it works -- but nothing out of Program Files seems to work). Anyways, I can do this, so far: C:\py django-admin C:\py python "C:\python26\Lib\site-packages\django\bin\django-admin.py" Type 'django-admin.py help' for usage. C:\py django-admin startproject myProj C:\py python "C:\python26\Lib\site-packages\django\bin\django-admin.py" Type 'django-admin.py help' for usage. but the additional parameters don't get passed along to the batch script. This is getting very annoying, all I want to do is run python scripts :) How can I grab the rest of the parameters in this situation?

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• How to solve 'Badly constructed integrity constraints' in doctrine

  - by Carson

  When I execute the command './doctrine build-all-reload' It comes out the following output: build-all-reload - Are you sure you wish to drop your databases? (y/n) y build-all-reload - Successfully dropped database for connection named 'doctrine' build-all-reload - Generated models successfully from YAML schema build-all-reload - Successfully created database for connection named 'doctrine' Badly constructed integrity constraints. Cannot define constraint of different f ields in the same table. Here is the source code of Doctrine that outputs the error: here What causes the error? How can I debug where the error comes from?

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• Is it acceptable to wrap PHP library functions solely to change the names?

  - by Carson Myers

  I'm going to be starting a fairly large PHP application this summer, on which I'll be the sole developer (so I don't have any coding conventions to conform to aside from my own). PHP 5.3 is a decent language IMO, despite the stupid namespace token. But one thing that has always bothered me about it is the standard library and its lack of a naming convention. So I'm curious, would it be seriously bad practice to wrap some of the most common standard library functions in my own functions/classes to make the names a little better? I suppose it could also add or modify some functionality in some cases, although at the moment I don't have any examples (I figure I will find ways to make them OO or make them work a little differently while I am working). If you saw a PHP developer do this, would you think "Man, this is one shoddy developer?" Additionally, I don't know much (or anything) about if/how PHP is optimized, and I know that usually PHP performace doesn't matter. But would doing something like this have a noticeable impact on the performance of my application?

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• Can i configure emacs to use gdb like a graphical debugger?

  - by Joey Carson

  I'm pretty sure that this how other IDE's do it, e.g. on windows eclipse uses the output of gdb from MinGW (the windows port of GNU toolchain) to map where execution is in the source code and what values variables hold, etc. I'm stuck using gdb via a script that prepares our application in a chroot and does some other bootstrap for debug purposes. Once the script starts moving, the output is all gdb. Is there any way that I can configure emacs so that it will use gdb's output and allow for a sort of graphical debugger, comparable to that of eclipse or ms visual studio?

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• How should I build a simple database package for my python application?

  - by Carson Myers

  I'm building a database library for my application using sqlite3 as the base. I want to structure it like so: db/ __init__.py users.py blah.py etc.py So I would do this in Python: import db db.users.create('username', 'password') I'm suffering analysis paralysis (oh no!) about how to handle the database connection. I don't really want to use classes in these modules, it doesn't really seem appropriate to be able to create a bunch of "users" objects that can all manipulate the same database in the same ways -- so inheriting a connection is a no-go. Should I have one global connection to the database that all the modules use, and then put this in each module: #users.py from db_stuff import connection Or should I create a new connection for each module and keep that alive? Or should I create a new connection for every transaction? How are these database connections supposed to be used? The same goes for cursor objects: Do I create a new cursor for each transaction? Create just one for each database connection?

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• what's the difference between 'Apply Patch' and 'Share Project' in Eclipse for SVN?

  - by Carson

  Everytime before connecting to svn server, there are two 'Team' options: 'Apply Patch' and 'Share Project'. It seems to me that both options perform the same when intializing the svn project. What exactly is the difference?

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• Adding a method to a function object at runtime

  - by Carson Myers

  I read a question earlier asking if there was a times method in Python, that would allow a function to be called n times in a row. Everyone suggested for _ in range(n): foo() but I wanted to try and code a different solution using a function decorator. Here's what I have: def times(self, n, *args, **kwargs): for _ in range(n): self.__call__(*args, **kwargs) import new def repeatable(func): func.times = new.instancemethod(times, func, func.__class__) @repeatable def threeArgs(one, two, three): print one, two, three threeArgs.times(7, "one", two="rawr", three="foo") When I run the program, I get the following exception: Traceback (most recent call last): File "", line 244, in run_nodebug File "C:\py\repeatable.py", line 24, in threeArgs.times(7, "one", two="rawr", three="foo") AttributeError: 'NoneType' object has no attribute 'times' So I suppose the decorator didn't work? How can I fix this?

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