Let me give you an example to show Python’s awesomeness and attractiveness.

Refer to this page for the problem. We are asked to compute the first ten digits of the sum of one-hundred 50-digit numbers:

37107287533902102798797998220837590246510135740250
46376937677490009712648124896970078050417018260538
74324986199524741059474233309513058123726617309629
…

Suppose you are using C/C++, you probably need to use array to handle each digit of these long numbers, since these languages don’t support such long integers. If you are using Python, things will be very easy.

Just copy/paste these numbers into a file. Edit it with Vim. Use Vim command:

:%s/$/,/g

to add a comma to the end of each line. Remove the last comma. Then insert “array = [" to the beginning of the first line and add a "]” to the end of the last line.

Add the following to another line:

print sum(array)

Save this file and run it with Python and here we are done.

Here you can see that Python can handle arbitrary large number, as long as you memory can hold it. This is just a tip of the iceberg of Python’s advantage. Use it and you will get more and more.

On July 22, the solar eclipse occurred in the Yangtze River Basin in China. However, in my hometown, there was only partial eclipse. Following are some photos taken by me, with the assistant of a telescope.

before most eclipse

most eclipse

begin recovery

almost reoved

recoverd

Which editor are you using, Vim or Emacs? And why?

Next time, when you are arguing with other people about which editor is better and trying to persuade others to use your favorite editor, just forget it. If you believe everything is in destiny, it is not an exception for the editor you choose. The choice is written on your fingers.

Several days ago, I learnt from Mike that the choice between using Vim or Emacs depends on your fingers. As he figured out, people have longer fingers prefer to use Vim, while people have shorter fingers prefer to use Emacs. It is amazing, but reasonable.

Using Vim, the most frequent key you hits might be the “Esc”. Vim has three modes: insert mode, command mode and visual mode. Command mode is the bridge of other two modes, and most of navigating and searching is done in command mode. So, when you are using Vim, you must: press “a” or “i” to start insert mode and input something, then press the “Esc” to enter the command mode and do navigation, then enter the insert mode again and then press the “Esc” to the command mode. Maybe some times you want to hit “v” to enter the visual mode to select something, and after that you must hit the “Esc” again back to the command mode. At most time, you are hitting the “Esc”. That’s why they call Vim “hit Esc to death”. Of course, you also need Ctrl and Shift in vim, but not so often. For example, when you select contents by line or by block, you will press “Shift+v” or “Ctrl+v”. When you want to jump to the end of a line, you will press “$”(Shift+4). But these cases are much rearer than hitting the “Esc”. So, when your fingers are long enough, you will find it very comfortable and easy to hit the “Esc”. Maybe that’s why you like to use Vim.

I have touched Emacs for little times. In Emacs, almost everything except for inputing text are done by “Ctrl+something”, “Shift+something”, “Alt+something”, or even “Ctrl+Alt/Shift+something”. That means at most time, one of your finger must hit “Ctrl”, “Shift” or “Alt”. That’s why they call Emacs “hit Ctrl to death”. Some Emacs fans even want to use pedals to help them hit hot keys. I have to twist my fingers to hit those keys. For some complicated combination of keys, I even don’t know how to hit them comfortably and elegantly. So I gave up Emacs soon to save my hands and fingers. Maybe people who have shorter fingers would fall in love with Emacs because they could hit these hot keys easily without twisting their fingers very much.

Although I prefer Vim, I don’t mean to comment Emacs and Emacs users. Emacs is also powerful, and even more powerful than Vim (at least in my mind). I admire Emacs users very much because they can learn so many hot keys by heart and use them gently and easily.

If you are still confusing about choosing Vim or Emacs, just check your finger. If your fingers are longer than most of your friends, then just choose Vim without hesitate and you will like the life of hitting the “Esc”. If your fingers are shorter than average and you find it’s uncomfortable to hit the “Esc” frequently, then you should definitely choose Emacs.

If you are still arguing with other people about Vim and Emacs, forget it, unless you want to cut some one’s finger to force them to use Emacs or lengthen some one’s finger to force them to use Vim.

If you are jeered by Emacs users for you are using such a disharmonious editor that has multiple confusing modes, you could respond them, “at least I have beautiful long fingers”. If you are sneered by Vim users for you are using such a complicated editor that requires a pedal to handle the hot keys, you could respond them, “at least my memory is better than you, since I could remember thousands of hot keys”.

Most people prefer webmail, especially Gmail. Webmail is very easy to use and does not require much configuration. Gmail is the most wonderful webmail. It groups messages by threads and it has a powerful searching tool. You can easily find out what you want from the mass.

However, one drawback of webmail is that you cannot access your mail off-line. Although Gmail started to support off-line email recently, I still think that keeping the emails in my local storage is safe and reliable. Moreover, an email client is generally much more customizable than webmail. So, I am using Evolution, which is the most powerful and standard email client in Linux, to receive and send email everyday.

As said in the beginning, I want to figure out what email clients my contacts are using. This work is not hard. There might be some fields in the header of email indicating which client this email is generated. The field could be named “X-Mailer”, “X-mailer”, or “User-Agent”. In Evolution, you can open the menu “Edit>Preferences>Mail Preferences>Headers”, and check the “Mailer”. Then you could see the Mailer information in your mails. Some mails are composed without the Mailer information. I don’t know why. We just ignore the mails without Mailer information.

Evolution stores mails in the folder “~/.evolution/mail/local/Inbox.sbd”. Under this folder, the files without extension are the mail files, which included all the contents of your mail. So, we can grab Mailer informations from these files.

First, we can use “grep” to filter the lines containing “X-Mailer”, “X-mailer”, and “User-Agent”. We can store them into a file.

cat mail-box-name | grep X-Mailer > outfile

cat mail-box-name | grep X-mailer >> outfile

cat mail-box-name | grep User-Agent >> outfile

“mail-box-name” is the name of the mail files. Carefully name the outfile. Don’t let it overwrite the existing file. My suggestion is that you can copy all the mail files to another place and do these operations there. It’s safe.

Now we get the outfile containing Mailer information. The next step is removing useless information from this file, such as the header “X-Mailer” or the version information. This is the most boring part. Maybe there are some sophisticated methods which could do this work automatically, but I am lazy to think them up. For me, I use Vim and block-edit the text (ctrl+v, then move cursor), and this work is done without much effort. Now we get the file like this:

…
Moto-EZX
Moto-EZX
Moto-EZX
Mozilla
Mozilla
Mozilla
Mutt
Mutt
…

Then we should count them. Use this command:

uniq -c inputfile > outputfile

Finally we get the file like this:

…
84 Evolution
182 Foxmail
1956 G2/1.0
…

Maybe we need some refinement for these data. For example, remove the very rare entries (e.g < 10), and remove the entries that are obviously web server, such as “ASPMail”, “PHPMail”, etc.

After refinement, there we come to the OpenOffice Spreadsheet for analyzing these data. Again, we use Vim and block-editing to separate the count and client name, and paste them into Spreadsheet individually. Then open “Insert>Chart” and generate your favourite chart.

Following is my data, in which the size of sample is 3003 (after refinement):

From the chart we can see the most popular email client of my contacts is Gmail (G2/1.0). Following are Thunderbird and Foxmail. Then it comes Evolution, Apple Mail, SquirrelMail, Outlook and SFUwebmail.

Which client are you using?

For me, the must-have feathers of a source browsing tool should be:

1. Syntax highlighting
2. Friendly user interface
3. Identifier and function search

If you are a Windows user, you might have heard about Source Insight, which is a non-free software. I haven’t used it, so I am not going to comment it.

For Linux user, the first tool I want to mention is Source Navigator. It is developed and supported by Red hat. It supports C, C++, Java, Tcl, FORTRAN and COBOL. It’s very powerful. But if you just want to browse sources, I don’t recommend you to use it. Since it GUI is developed in Tcl, an ancient programming language, the user interface is not very friendly. I bet you don’t like it.

Another wonderful software is Doxygen. Although it aims to generate documents various programming languages, including C++, C, Java, Objective-C, Python, IDL (Corba and Microsoft flavors), Fortran, VHDL, PHP, C#, and to some extent D, you can treat it as a source browsing tool. It can generate documents in HTML format. So you can read them via Firefox. If the source code is well commented following JavaDoc’s style, a beautiful documents describing classes, variables, functions could be generated. If the source code is not commented in JavaDoc’s style, the documents could also be generated, but it just have source codes, without these detailed description about classes, variables, and functions. Doxygen can also generate class-graphs, call-graphs and other similar graphs in UML style, which will help you understand the source.

The disadvantage of Doxygen is that its search result is somehow coarse-grained. It cannot distinguish variables from functions in search result. And it cannot differentiate definition, declaration and reference. So, if you are dealing with a huge project, you may find it uncomfortable to read source generated by Doxygen.

The ultimate tool, in my view, is LXR, which stand for Linux Corss Referencer. Specially, it may be the best choice for you to read Linux source code. Although, namely, LXR aim for Linux source code, it suitable for other projects written in C/C++, COBOL, Java, Perl. It is a web based tool and you can read the source code via Firefox. It uses a database to management cross references. So the search result is very accurate. And it can differentiate definition, declaration and reference.

LXR is famous for its difficulty on setup and configuration. And its user interface cannot be called “beautiful”. Luckily, the next generation, LXRng (demo) is available now. LXRng has a very beautiful and friendly user interface.  Moreover, setup and configuration for LXRng is much simpler than LXR. However, it seems that LXRng currently only support C language. If you need it for C++, you need a slight hack:

Locate to your LXRng’s installation directory, then open this file:

lib/LXRng/Lang/C.pm

Find the following code from this file:

sub pathexp {
    return qr/\.[ch]$/;
}

And change it into:

sub pathexp {
    return qr/\.[ch]$|\.cpp$/;
}

Then LXRng should support the C++ files.

Doxygen and LXRng could satisfy most of your requirement. Maybe reading source from Firefox is strange and unfamiliar to you, but I think you will going to like it if you just have a try. If you have no idea about how to use them, just go to their websites, where you can find plenty of documents and toturials.

I just created my first video DVD. My experience may help you get less trouble on burning your video DVD on Ubuntu/Linux.

Most DVD videos are encoded in MPEG-2 format. So, if your original video is not encoded into MPEG-2, the first thing you need to do is to transcode it into MPEG-2. There are lots of powerful tools to handle it, such as ffmpeg and mencoder. They are command-line tools. If you are a crazy fan of command line, you definitely should try them. However, the command line arguments will generally be 10 lines! If you cannot handle them(like me), just try some GUI tools.

The first option is Avidemux. It’s powerful and easy to use. However, its H264 support is poor. When I tried to transcode a H264 video into MPEG-2, it crashed every time. Maybe it works fine with other format, but I have no chances to take a try.

Another great transcoding tool is Hyper Video Converter. It’s a front-end of ffmpeg and mencoder. Although it looks a bit “Shanzhai”, it’s more powerful than its appearance, since it’s the frontend of powerful ffmpeg and mencoder. It’s quite reliable. I used it to transcode my H264 “mkv” file into MPEG-2 “mpg” file. I recommend you to use it, if you have no requirement on gaudy appearance. The KDE version is here.

Then it goes to create DVD file structure. Generally, we need a folder contains VEDIO_TS and AUDIO_TS folders and put some necessary information files in them. This work can be done by dvdAuthor. It’s also command line based tool. As introduced in its website, there are several frontend for it. The most famous one is QDvdauthor. The newest version for Hardy in Getdeb is 1.5.0, which is even lower in repository. 1.5.0 has much bugs in creating subtitles, You should use the newest version, 1.7.0, which is available in Getdeb for Intrepid. I am using Hardy, so I compiled 1.7.0 and created a deb package by myself. Grab it if you need.

Now, we are using QDvdauthor 1.7.0. Just create you your DVD file structure using the MPEG-2 video encoded by Hyper Video Converter. There are some tutorials for QDvdauther. Just take a tour if have problems on how to start.

Once you get the DVD file structure including VIDEO_TS and AUDIO_TS, you can test them via VLC or SMPlayer. Take SMPlayer for example, select “Open”->”DVD from folder” to test the video.

If everything works, you can create an ISO image. I recommend you to create ISO image and burn image by your self, using genisoimage and K3B. Because there are much things that you can control. The most important thing is that current version of genisoimage has a huge bug. The image created by it is not readable by Windows and standalone DVD machine. This bug is not solved in even the latest version 1.9.0. You have to downgrade you genisoimage into 1.2.0 from debian repository.

One thing that QDvdauther cannot control is the volume name of the image. This is why I recommend you to create ISO image by yourself. You can use this command:

genisoimage -dvd-video -udf -V “Volume-Name” -o “dvd.iso” “DVD-folder”

“dvd.iso” is the ISO image you are going to create. And “DVD-folder” is the folder contains VEDIO_TS and AUDIO_TS folders.

Then, add the Error Correction Codes(ECC) to the image

dvdisaster -i “/tmp/Unnamed/dvd.iso” -mRS02 -n 350000 -c

If this command issues error message, maybe you should remove the option “-n 350000″ or adjust it.

At the last step, burn this ISO image by whatever software you like.

Enjoy your video DVD created on Ubuntu/Linux!

Following is the deb package of QDvdauthor 1.7.0. It could be installed on Ubuntu 8.04.

qdvdauthor-170_deb

Here, only English contents will appear from now on. All the old articles in both languages here will be reserved. I will use this blog to post some technique articles related to Linux, programming in English. It should be a good way to practice my English writing.

My Chinese blog: http://blog.chunhao.net

Originally, each part had its own theme. It’s hard to acces other parts directly from one part. For example, there are no links from my blog or wiki to my homepage. I decided to change this. Eventually, the goal is achieved.

The theme of my blog is blue-pix. I like it for its briefness. The first thing I did is to port this theme on my home page. This work is pretty simple. I only changed the tags of the CSS file. Then, I modified the blog’s theme, added a link to homepage. The themes of homepage and blog was unified.

Next thing is my wiki. I have no idea about how to create template on dokuwiki at the beginning. When I refered to this link, I started my work. I did a lot of change on CSS and PHP files. Finally, my own template of dokuwiki was created. Now the themes of the whole site is unified, except for the photo gallery.

For the blog’s theme, blue-pix, I also did lots of modification. The originally version did not support widget, and it did not support Google Analytics and other things. It also did not support thread comments. Now, it works fine. If you are interested in this theme, just feel free to contact me.

I am not an expert on PHP, CSS, and HTML. However, I like hacking. All the problems are solved with the help of Google. I believe one sentence–don’t learn to hack, just hack to learn.

———–

Supplement:

Just now, I finished the modification of my photo gallery. Now, everything in my site are following the same theme!

The wiki I used in my homepage is Dokuwiki. The most great feature is that it does not require database connection. It’s very convenience for personal usage.

I have two Dokuwiki maintained. One is located in localhost, another in the webserver. I always edit the pages on localhost, and synchronize them to the webserver at times. Since Dokuwiki is totally PHP based, without database such as MySQL, I only need to synchronize some files.

All the changes on wiki are reflected on the folder “data” in your Dokuwiki path. So every time, I only need to synchronize this folder.

The best way to communicate with webserver is SSH. Fortunately, my webserver Godaddy support SSH access. Another thing need to concern is synchronizer. Here I use Unison. The best description of Unison comes from it’s the author of this software:

A file-synchronization tool for Unix and Windows
Unison is a file-synchronization tool for Unix and Windows, written
in OCaml. It allows two replicas of a collection of files and
directories to be stored on different hosts (or different disks
on the same host), modified separately, and then brought up to
date by propagating the changes in each replica to the other.

Unison offers several advantages over various synchronization methods
such as CVS, Coda, rsync, Intellisync, etc. Unison can run on and
synchronize between Windows and many UNIX platforms. Unison requires
no root privileges, system access or kernel changes to function. Unison
can synchronize changes to files and directories in both directions,
on the same machine, or across a network using ssh or a direct
socket connection.

Transfers are optimised using a version of the rsync protocol,
making it ideal for slower links. Unison has a clear and precise
specification, and is resilient to failure due to its careful
handling of the replicas and its private structures.

If you are using Ubuntu machine, you can install it from the repository just by one command:

sudo apt-get install unison

There is also a gtk front-end for this software: unison-gtk, but I think it’s useless at most time.

Now, another problem comes to front–in order to synchronize files with SSH, both installations of Unison on client and server are required. However, at most time, you don’t have the permission to install software such as unison on SSH server. Here, we attack this issue by SSHFS. It allows you to mount a remote folder on your machine via SSH.

Everything is OK. I wrote a small script to handle the synchronization:

#!/bin/sh
sshfs -o workaround=rename username@sshserver:/path/html/wiki wiki-remote/
echo "Synchronising with sshserver"
unison /var/www/dokuwiki/data ./wiki-remote/data \
  -fastcheck yes \
  -ignore 'Path cache' \
  -ignore 'Path locks'

Modify it to fit your actual environment. Note that the argument of sshfs command “-o workaround=rename”, this prevents the “renaming problem“.

All things done. Excute this script. Or, you could add an cron job to run this script automatically once per day. Have fun in synchronizing files with SSH!

I am using 000webhost for the old site, which is really a good free host provider. However, due to my misoperation,  the new domain cannot be located in the free web host any more. I switched to another non-free host provider–GoDaddy.

Now, most part of the site have been transferred to the new domain here. All the posts and comments in my blog have also been moved properly. The old domain(chunhao86.cn) will keep alive for a long time. However, no upgrading will be presented there any more.

Most things are the same with old ones, except for some some changes. There most significant is  WordPress. This new blog is built using WordPress 2.7, while the old one WordPress 2.3. There are lots of changes between the two versions, escpecially in the admin page. The new version is more user-friendly and integrated with much new feathers. Thanks for the small quantity of the posts and comments in my old sites, it’s very easy to move them correctly!

So sorry for you inconvenience! And thank you for touching my new site here. Please keep trace of my new site: http://chunhao.net, as well as my blog: http://chunhao.net/blog.