http://www.chrisspen.com/blog knowledge through programming Sat, 28 Jan 2012 11:53:31 +0000 http://backend.userland.com/rss092 en Since I couldn't easily find this code anywhere, I figured I'd post it here for quick reference: """ 2012.1.25 CKS Incremental calculation of both the mean and variance. http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance """ import unittest ## Dumb slow mean/variance formulas. def mean(seq): return sum(seq)/float(len(seq)) def variance(seq): m = mean(seq) return sum((v-m)**2 for v ... http://www.chrisspen.com/blog/online-variance-calculation-in-python.html After running Django unittests, it may sometimes be useful to manually inspect the test database after unittests are complete. I was working on a complicated network model, trying to resolve an elusive bug in a unittest, and in this specific instance, I thought running a manually written SQL query would ... http://www.chrisspen.com/blog/persisting-djangos-test-database.html I was doing some work with an inherited Kerberos setup, when I noticed my Kerberos-based SVN login suddenly stopped working. Attempting to ssh into the machine revealed the cause: WARNING: Your password has expired. You must change your password now and login again! Fair enough. I personally find password expiration a huge annoyance ... http://www.chrisspen.com/blog/passwd-authentication-token-manipulation-error.html Django has a great auto-generated administration interface. It's saved me countless hours of development time and makes basic data maintenance a breeze. Although it's designed to be extensible, it's not without it's quirks and hurtles. Fortunately, most of these can be overcome with a little code inspection. One of these ... http://www.chrisspen.com/blog/restricting-write-access-to-django-admin.html When I originally wrote html2text.py, my focus was only on extracting English text from webpages, so I didn't give much thought to handling Unicode. Ignoring anything but ASCII would suffice. However, I was recently commissioned to extend the script's functionality to use Unicode, so it could extract text in nearly ... http://www.chrisspen.com/blog/how-to-extract-a-webpage%e2%80%99s-main-article-content-the-unicode-edition.html Festival is a great text-to-speech engine. MBROLA also contains some impressive voice files that have notably higher quality than Festival's default voices. Both of these systems are packaged in Ubuntu, and even though Festival can use MBROLA's voice files, as of Ubuntu 10.04, there doesn't seem to be a package ... http://www.chrisspen.com/blog/how-to-install-mbrola-voices-for-use-with-festival-on-ubuntu.html I was researching methods to encrypt USB flash drives, to protect personal data in the event they're lost or stolen, and I found a few good write-ups on the subject using tools available in Ubuntu. Although the current distribution of Gnome includes pretty good support for auto-detecting and prompting for ... http://www.chrisspen.com/blog/ubuntu-flash-drive-encryption-script.html I was researching simple methods for backing up a basic Linux web server, and I found an excellent script that handles files and databases, and also dumps everything to a remote server. I was looking for something a bit less complicated and overkill than Bacula, but more comprehensive than simply ... http://www.chrisspen.com/blog/how-to-remotely-backup-a-web-server-with-no-install.html Rock-paper-scissors is not a complicated game. However, there are some that not only enjoy the game, but take pride in professing skill at it. But is it possible to have skill at rock-paper-scissors? In the real world, where a human plays against a human, "cheating" is relatively easy. A player can ... http://www.chrisspen.com/blog/implementing-a-simple-machine-learning-intelligence-to-play-rock-paper-scissors-in-javascript.html I have some basic Django code that attempts to insert a new record into a PostgreSQL database. It's wrapped in a try/except statement in case a unique constraint is violated, in which case I'll typically ignore it and move on. So the general pattern is: from django.db import IntegrityError import models try: ... http://www.chrisspen.com/blog/handling-postgresql-integrity-errors-in-django.html