Guy Rutenberg

Few days ago I came up with an idea to create a true random number generator based on noise gathered from a cheap microphone attached to my computer. Tests showed that when sampling the microphone, the least significant bit behaves pretty randomly. This lead me to think it might be good source for gathering entropy for a true random number generator.
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It has been three years since I’ve released the original version of cssrtl.py (and two since it’s re-release). The old version did a nice job, but experience gained during that time led me to write from scratch a new version. I’ve detailed more than a month ago, the basic principles and ideas that guided me to design a better tool to help adapting CSS files from left-to-right to right-to-left.

The guidelines weren’t just empty words, they were written while working on the Hebrew adaptation to the Fusion theme and in the same time writing a new proof-of-concept version of cssrtl.py. The original intent was to release a more mature version of that code when it will be completed. However, due to the apparent shortage of time in the present and foreseeable future, I can’t see myself complete the project any time soon. So following the “release early” mantra, I’ve decided to release the code as-is. As I said, the code is in working state, but not polished, so it may be of benefit but may contain bugs. If you find any bugs or have any suggestions, I would be glad to hear.
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When I first scratched the itch of calculating checksums for every file in a tar archive, this was my original intention. When I decided I want the script in bash for simplicity, I forfeited the idea and settled for extracting the files and then going over all the files to calculate their checksum value.

So when Jon Flowers asked in the comments of the original tarsum post about the possibility of getting the checksums of files in the tar file without extracting all the archive, I’ve decided to re-tackle the problem.

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Damerau-Levenshtein Distance is a metric for measuring how far two given strings are, in terms of 4 basic operations:

• deletion
• insertion
• substitution
• transposition

The distance of two strings are the minimal number of such operations needed to transform the first string to the second. The algorithm can be used to create spelling correction suggestions, by finding the closest word from a given list to the users input. See Damerau–Levenshtein distance (Wikipedia) for more info on the subject.

Here is an of the algorithm (restricted edit distance version) in Python. While this implementation isn’t perfect (performance wise) it is well suited for many applications.

"""
Compute the Damerau-Levenshtein distance between two given
strings (s1 and s2)
"""
def DamerauLevenshteinDistance(s1, s2):
    d = {}
    lenstr1 = len(s1)
    lenstr2 = len(s2)
    for i in xrange(-1,lenstr1+1):
        d[(i,-1)] = i+1
    for j in xrange(-1,lenstr2+1):
        d[(-1,j)] = j+1
 
    for i in xrange(0,lenstr1):
        for j in xrange(0,lenstr2):
            if s1[i] == s2[j]:
                cost = 0
            else:
                cost = 1
            d[(i,j)] = min(
                           d[(i-1,j)] + 1, # deletion
                           d[(i,j-1)] + 1, # insertion
                           d[(i-1,j-1)] + cost, # substitution
                          )
            if i>1 and j>1 and s1[i]==s2[j-1] and s1[i-1] == s2[j]:
                d[(i,j)] = min (d[(i,j)], d[i-2,j-2] + cost) # transposition
 
    return d[lenstr1-1,lenstr2-1]

Some time ago, as some of you noticed, the web server that hosts my blog went down. Unfortunately, some of the sites had no proper backup, so some thing had to be done in case the hard disk couldn’t be recovered. My efforts turned to Google’s cache. Google keeps a copy of the text of the web page in it’s cache, something that is usually useful when the website is temporarily unavailable. The basic idea is to retrieve a copy of all the pages of a certain site that Google has a cache of.
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As part of a server move, I went on to reinstall Trac. I’ve tried to install it as FastCGI but I failed to configure the clean URLs properly. I got the clean URLs to work if the user access them, but Trac insisted on addeing trac.fcgi to the beginning of every link it generated. So I’ve decided to use the Trac standalone server, tracd.

The next problem I faced was how to start the Trac automatically upon startup. The solution was to use an init.d script for stating Trac. After some searching, I didn’t find an init.d script for tracd that were satisfactory (mostly poorly written). So I went on an wrote my own init.d script for tracd.
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This is a re-release of a script of mine that helps convert CSS layouts to RTL. I originally released it about a year ago but it was lost when I moved to the new blog. The script, cssrtl.py, utilizes a bunch of regular expressions to translate a given CSS layout to RTL.

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Python 2.5 introduced new syntax structure: the conditional expressions. For programmers in languages such as C these structures seem very basic and fundamental but Python lacked them for many years. As I said Python 2.5 introduced such syntax structure, one may use it in the following form:

x =  a if condition else b

As you probably guessed a is assigned to x if condition evaluates to true and b is assigned otherwise. This is pretty much equivalent to the C conditional expressions. But as I said, this structure was only introduced in 2.5. Previous versions of Python are still widely deployed and in use, so how do you achieve the same thing in older version of Python?
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Download radio-0.3.tar.gz.

Update: radio.py-0.4 is now available.

I like listening to music and radio while working, and fortunately there are numerous ways to do that. Unfortunately, most ways that allow you to listen to radio are very resource consuming/memory hogs (such as listening to streaming-media via web-browsers) or very unfriendly to users (listening via mplayer for example). So, I set out to find a way that will use as little system resources as possible while keeping it user-friendly. One other requirement that I had, that I will be able to do all that from the command-line, so it will work great with GNU Screen and won’t require an X server (if I work without one).

I used for some time mplayer for listening to radio. I had a file with a list of web-radio streams URLs which I would copy and pass to mplayer -playlist. This method answered two of the requirements (minimal resources and command-line interface), but wasn’t really user friendly. So, I wrote a little wrapper script in python around mplayer – radio.py. After quick installation (download and extract the tar archive and copy radio.py to somewhere in you PATH), radio.py will allow you to listen to stations easily, and it will also do couple more things for you.

To listen to a station just call radio.py with the station’s name, e.g. in the command-line enter radio.py BBC1 to listen for BBC radio channel 1. To view a list of know stations run radio.py --list. Currently there aren’t many stations (just stations I thought that are needed or I listen to). You can easily edit radio.py to add new stations (the script is documented and very clear). If you do so, please write a comment or email me so I will be able to add those stations to next release by default.

So, as you seen radio.py allows you to easily listen to radio, as easy as writing the station’s name. But, as I said, it can do more things that I thought should be in a radio script. It has both a sleep feature (that turns off the radio after specified amount of time) and a wake-up feature (that starts the radio after a specified amount of time). This two features can be used together, and practically allow you to use radio.py as an alarm clock.

You can find more information about radio.py options by calling radio.py --help. I hope you will find this script useful as I do.

Download:
radio-0.3.tar.gz.

I use KDevelop as my main IDE and I’m pretty satisfied. KDevelop can create a source archive of the project’s source code automatically for you which simplifies the distribution of the project. Unfortunately the archive created isn’t ready for distribution. The user can’t just run ./configure ; make as he needs to run all the automake tools before. Not ideal for distributing. So you need to convert this source archive to a source package which is ready for the user to compile immediately

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