I learned today that python generators can be run in reverse to create coroutines. The basic idiom is:

def myCoroutine():
while True:
x = (yield)
doSomethingTo( x )

Then you can use it by calling .send() to provide the return value of the yield expression. See a short course here: Read more... )

A python for-loop can take any sequence as an argument, but sometimes you want both an index and the elements of a sequence. One way is to loop over the indices:

for i in xrange(len(sequence)):
e = sequence[i]
# do something with both i and e

The idiom I hadn't come up with on my own was:

for i, e in zip(range(len(sequence)),sequence ( Read more... )

At Kealia, we had a debug interface to our system, consisting of an embedded Tcl interpreter, accessible via a telnet server written in Tcl.

"Mark", I said to myself, "what are the odds that somebody has done this in Python?"

Pretty good, it turns out.The Twisted framework, in addition to making it easy to write your own telnet/SSH/whatever ( Read more... )

I wrote my first multi-threaded Python program today. I discovered that if your main thread waits for the others with join() then the program can no longer be interrupted with Control-C. Guido himself says "you'll just have to live with this."

Here's the "makefile" for an example unit test:

# -*- python -*-
# test/unit/example

Import( 'testEnv' )

testEnv.UnitTest( 'example', ['factorial.cpp', 'fixture.cpp'] )
testEnv.UnitTest( 'example2.py' )
This is sufficient to compile the C program, and run both unit tests. If there was an install step, it wouldn't require any additional code in ( Read more... )

The software practice at Kealia (and, I hope, at the new company) is to perform builds in a separate directory structure from the source tree. This makes it fairly easy to have separate release and debug builds coexisting, try out different optimization options in parallel, or be really sure that you're doing a clean build. It also makes it a ( Read more... )

Here's a line of python code to turn a 1-1 dictionary fwdMap into its inverse.

revMap = dict( [ tuple( reversed( x ) ) for x in fwdMap.items() ] )

Is there a better version? Well, tuple/reversed is overkill for a two-element tuple; this version is a bit shorter but I hate using indices.

revMap = dict( [ (x[1],x[0]) for x in fwdMap.items() ] )
A ( Read more... )

If you want to iterate from 0...N-1 in Python, you use

for i in range(0, N):
What if you want to iterate from (N-1)...0? I came up with

for i in reversed( range( 0, N ) ):
as the easiest-to-understand version, but is this the standard Python idiom? Yucky alternatives:

for i in range( N-1, -1, -1 ):

for fi in range(0, N):
i = N-1 - fi