Popular recipes by Shannon -jj Behrens

WalkRecursiveGenerators (Python)

2007-11-29T19:20:33-08:00

Python recipe 535145 by Shannon -jj Behrens (algorithms). Revision 3.

Walk a tree of generators without yielding things recursively. Check out the docstring. It has an example ;)

GroupBySorted (Python)

2008-08-08T23:48:22-07:00

Python recipe 499379 by Shannon -jj Behrens (algorithms). Revision 5.

Updated: Use itertools.groupby instead. See my comment below.

This is a variation of itertools.groupby. The itertools.groupby iterator assumes that the input is not sorted but will fit in memory. This iterator has the same API, but assumes the opposite.

ProtectUTF8 (Python)

2006-04-28T06:46:25-07:00

Python recipe 492223 by Shannon -jj Behrens (text).

protect_utf8 is a function decorator that can prevent naive functions from breaking UTF-8.

TryFinally (Python)

2005-10-17T22:37:51-07:00

Python recipe 442419 by Shannon -jj Behrens (algorithms).

This is a convenient way to deeply nest try/finally statements.

RunningCalc (Python)

2005-02-18T23:22:55-08:00

Python recipe 363786 by Shannon -jj Behrens (programs). Revision 2.

This is a trivial calculator "shell" with a running total. As trivial as it is, I find it to be more useful than a normal calculator when doing my checkbook because of the ever-present running total.

Sed is to Vi as RunningCalc is to Python

python ~/programming/python/hacks/RunningCalc.py $ 0.0+50 $ 50.0-10 $ 40.0*0 $ 0.0+5 $ 5.0-2 $ 3.0

FunctionDecorators (Python)

2005-02-15T02:48:07-08:00

Python recipe 363779 by Shannon -jj Behrens (shortcuts). Revision 2.

Use a function decorator to tell when and how a function should be logged. All kinds of things can be logged automatically, including the function arguments and (theoretically) even the stack.

InverseExtendGenerators (Python)

2005-01-19T18:46:46-08:00

Python recipe 363782 by Shannon -jj Behrens (oop). Revision 2.

This is the same as InverseExtend, except it uses a yield for non-local flow of control in a way yield wasn't really meant to be used ;)

AutoLoader (Python)

2005-01-19T18:34:03-08:00

Python recipe 363772 by Shannon -jj Behrens (oop). Revision 4.

If you have an instance "db", then accessing "db.Foo" automatically imports, instantiates, caches, and returns an instance of "Foo" from the "db" package.

ThreadSafeProxy (Python)

2005-01-19T10:16:49-08:00

Python recipe 363777 by Shannon -jj Behrens (threads).

This is a proxy for an instance of some class called Foo. Any thread can use the one proxy, and the proxy will automatically look up the thread specific instance of Foo. This is great if you have a global function in someone else's code that you need to swap out for something "thread safe".

InitReplacement (Python)

2005-01-19T10:54:34-08:00

Python recipe 363785 by Shannon -jj Behrens (oop).

Hack a class's __init__ method without subclassing the class because a) you can't modify the original class and b) you can't modify other classes already using the first class. This is a gross hack that should only be used to work around flaws in libraries you have no control over. I've changed the names to protect the innocent.

ClearModules (Python)

2005-01-19T17:55:17-08:00

Python recipe 363774 by Shannon -jj Behrens (algorithms). Revision 3.

Clear "sys.modules" of stale code without having to restart your server. It's a hell of a lot harder to do right then it sounds.

Forward (Python)

2005-01-19T10:20:35-08:00

Python recipe 363778 by Shannon -jj Behrens (shortcuts).

Calling the "forward" method transfers processing to a new screen. It never returns. This code is taken from multiple places, so I haven't bothered to keep the classes intact, I've just taken the meat. More generally, this is an example of state machine with a main loop. At any point, you can say, "I'm ready to change state. Do it. Go back to the loop. Don't return--just throw away my current stack."

PackagePath (Python)

2005-01-19T18:40:54-08:00

Python recipe 363781 by Shannon -jj Behrens (oop). Revision 2.

If you have a hierarchy of packages in a library, permit the user of your library to have his own hierarchy of packages that "overlays" yours. That means he can even have classes named the same as your classes, and have his classes "shadow" yours. It also means that a project can be broken up into several top-level directories, all of which have the same package hierarchy within.

Curry (Python)

2005-01-19T18:02:22-08:00

Python recipe 363775 by Shannon -jj Behrens (shortcuts). Revision 2.

Suppose you have a function "sum(a, b)". This class lets you do things like:

plus4 = Curry(sum, 4)
print plus4(5)

AutomaticClass (Python)

2005-01-19T17:50:41-08:00

Python recipe 363773 by Shannon -jj Behrens (shortcuts). Revision 2.

BASIC IDEA: Using this class as a base class, you can quickly create new classes that know what its attributes are. This is useful for simple, struct-like classes that have no methods of their own. Afterall, class syntax is more convenient than dict syntax.

InverseExtend (Python)

2005-01-19T10:46:22-08:00

Python recipe 363783 by Shannon -jj Behrens (oop).

This is like the object oriented concept of extending a super class. However, instead of starting at the furthest subclass and working your way up, you start at the top super class and work your way down.

LazyGettext (Python)

2005-01-19T10:50:26-08:00

Python recipe 363784 by Shannon -jj Behrens (oop).

In some code I have to work with but don't have much control over, there are a bunch of strings declared at the module level. I need to figure out what all those strings are, and wrap them in something. Once they are wrapped, they must behave as strings, but lazily "translate" themselves whenever used in order for internationalization to work. Since each Web request might request a different language, I can't just do this once and be done with it.

HasFriends (Python)

2005-01-19T10:35:19-08:00

Python recipe 363780 by Shannon -jj Behrens (oop).

Permit anyone to add methods to a class in a library without having to change the name of the class by subclassing. This is like having a plugins directory. Also, given a normal function, treat it as a method of an arbitrary class (i.e. mimic a bound method).

ExtendedIfElse (Python)

2005-01-19T10:11:13-08:00

Python recipe 363776 by Shannon -jj Behrens (shortcuts).

A million things can go wrong, and there are several ways to succeed. You want to check for the ways that can succeed and continue on as soon as one of them does. You want the non-local flow of control that exceptions provide, but you need it for both success and failure.