Bullet on my own foot: trying to uninstall Python 2.6 from Ubuntu 9.10 Karmic Koala

Some major Linux distros use Python for maintaining their packages. Red Hat (and its downstream distros) which use the yum tool uses Python 2.4. I tried to install Python 2.6 in CentOS 5.4 without success. The tool rejected to install Python other than 2.4 using that tool out of fear that it will interfere with the tool.

I just found another catch, when you are trying to install Python 2.6 in Ubuntu (I was using Karmic Koala, 9.10), such as:
[source lang='shell']
$ sudo apt-get remove python2.6
[/source]

It will display the components that are about to be removed.
Kids, don't try this at home!
It will remove your whole desktop related application! Java, Gnome, apt tools. You practically will be left with command line Linux, and without the apt tools.

Uninstalling Python 2.6 from Ubuntu seems to be an act of shooting own's foot!

Lucky I tried on not-so-important experimental Ubuntu installation on my laptop.

Mercurial Server 1.0.1 Installation on Ubuntu

When we are working using Subversion, we can expose the Subversion repository using svnserve (open the default port 3690 and svn:// protocol) or leverage the Apache WebDav to expose your Subversion service in HTTP (the web protocol -- I've always tempted to write it as HTTP Protocol which is incorrect as the last P letter stands for 'protocol').

And of course if you are just as lazy as I, you will use the CollabNet Subversion or Edgewall Trac.

Mercurial Server from Lshift is one way to achieve similar thing. Though it is named Mercurial Server, it is not a server in traditional client/server perspective. It leverages the SSH authentication to make it like a central repository where multiple user can access and serves the same purpose.

Surprisingly, it is very easy to install in an Ubuntu box.

[sourcecode lang="shell"]
$ sudo apt-get install mercurial-server
[/sourcecode]

Gotcha! You have it now.
With this Mercurial Server, you can access the server using:
hg clone ssh://<ssh-user>@<host-name-or-ip-address>[:<ssh-port-num>]/<folder>

[sourcecode lang="shell"]
$ hg clone ssh://mercurial@192.168.0.1/projects
[/sourcecode]

Attending Singapore Google Technology Group Meetup

 

Today I attended this Singapore Google Technology User Group Meeting. It's my first time to attend such a Google meetings. Some of previous meet ups had always fallen on the wrong days -- on the day that I have something else to do. Today I am glad to be able to make it, attended the meeting, and Wesley Chun, was the speaker. He presented 2 sessions, one about Python and the other one about Google App Engine.

This guy's a hardcore Python guy, wrote the Core Python series of book, and was a presenter in the PyCon Asia Pacific 2010, Singapore -- an event that has been held last 3 days. Awesome in depth knowledge, vast industrial experiences, and keep the talk flows fluent.

The rest about the meeting can be found here: http://www.sg-gtug.org/2010/05/sg-gtug-special-tutorial-session-june.html

Missed PUG monthly meeting, exploring Java byte code and BCEL

I missed yesterday's Python User Group Singapore monthly meeting. I had to finish certain document before leaving office yesterday, I couldn't make it.

Last night I was exploring this Byte Code Engineering Library (BCEL) from Apache. This library gives us a way to analyse, create and manipulate binary Java class file. This library has been used by a lot of Java frameworks and containers, as those frameworks need to add some instrumentation when deploying those components in those frameworks and/or containers.

Well, this is considered an advanced thing in Java. Java classes are stored as Java byte codes. When you compile a Java source code, you will have .class file which is a Java byte code file. Java byte code is a form of machine instruction (in this case Java Virtual Machine or JVM). So it's executable binaries for JVM. Java byte code also have opcode like assembly language.

There are 2 type of instruction sets:

1. stack machine
2. register machine

Stack machine operates on stack. Operands are the stack only. The first programmable scientific calculators released by Hewlett-Packard are stack machines (http://www.hpmuseum.org/). They operate in a Reverse Polish Notation. I remembered that my first one of my first Java programming assignment was to implement GUI application for a Reverse Polish Notation calculator. My Dad has his own story of owning one of these calculators and he used to be very proud of the magnetic stripe stored Moon Lander game. It's just a number only Moon Lander, but it's a game running on programmable HP calculator!

Other sample of stack machines that most of us still use is the Intel x86 math coprocessor instructions set. It uses registers that are organised as stack, which will rotate back when overflowing the boundary (of 8 registers).

Stack machines, because it's only operate on stack and usually only the last few data in stack, may have shorter instruction bits. Unlike register machines which usually take some of the bits to specify from which and which register the data is from, and to which register the result goes, stack machines enjoy the benefit of default operands, that is top 1 or top 2 of the stack. The result is always in the stack.

I think one of the main considerations why JVM uses stack machine is to pack as few numbers of bits in the opcode. As most JVM runs as virtual machine, there will be no performance advantages of having a lot of register which anyway stored in RAM by the virtual machines.

Ok, enough for the stack machine, now back to the BCEL it's exciting to touch back the assembly language, byte code, opcode, operand, and stuffs if you are really into  it. I try to code a bit and will share the code later.

What is Spring Python?

Spring Python takes the concept of the Spring Framework and applies them to Python. This means that we can take advantage of the features of Spring Framework such as Dependency Injection (Inversion of Control), aspect oriented programming (AOP), remoting, data access, transactions, and security, all with the same non-invasiveness style.

This means that:

• it will be easier to unit test software components (Python objects with standardized dependency injection)
• we can move cluttering code outside the object and have cross-cutting functionalities (aspect oriented programming)
• scalability of business objects by adding remoting
• transaction (ACID)
• security (interceptor based which won't allow outside world to touch your application unless they are really authenticated an authorized)
• you don't have to extends certain class in order to get all those features (non-invasiveness)

The project was started independently by Greg L. Turnquist, which later joined the SpringSource team as Project Lead for Spring Python project. He also authored "Spring Python" book from Packt.

Spring Python is now approaching version 1.1 with its second milestone before release 1.1.0.M2. Current stable release version is 1.0.0.

All about SpringPython can be found on its web site http://springpython.webfactional.com/

PyDev 1.5.6 has been released

PyDev is a plugin that enables users to use Eclipse for Python, Jython and IronPython development -- making Eclipse a first class Python IDE -- It comes with many goodies such as code completion, syntax highlighting, syntax analysis, refactor, debug and many others.

Fabio Zadrozny from Aptana, the author of PyDev plugin,  passed this information through mailing list:

This Release Highlights:

• Django integration:

• 
  
  
  
  • New Django project can be created through twizard
  
  
  • Can set an existing porject as a Django project (right-click project > pydev > set as django project) I think this is a kind of Eclipse's personality, like those of Maven2 plugins where you can declare that this project is a  Maven project
  
  
  • New Django project can be created throughtwizard
  
  
  • Can remove Django project config (righ-click project > django > remove django project config)
  
  
  • Custom actions can be passed to the configured manage.py through ctrl + 2 + dj django action -- if not action is passed, will open to choose from a list of previously used command
  
  
  • Predefined/custom actions can be used through right-clicking the project > django > select custom action
  
  
  • manage.py and settings module configured
  
  
  • Django shell (with code-completion, history, etc) available
  
  
  • Run/Debug as Django available
  
  
  • See: http://pydev.org/manual_adv_django.html for more details
  
  
  
  

• Find/Replace:
  
  
  
  • The search in open files is no longer added in the find/replace dialog and now works through Ctrl  + 2+  s word_to_find (in the PyDev editor) and if no word is passed, the editor selection is used
  
  
  
  

• Go to definition:
  
  
  
  • Properly works with unsaved files (so, it will work when searching for a definition on an unsaved file)
  
  
  • Properly working with Eclipse 3.6 (having FileStoreEditorInput as the editor input)
  
  
  
  

• Editor:
  
  
  
  • Automatically closing literals
  
  
  • Removing closing pair on backspace on literal
  
  
  • Improved heuristics for automatically closing (, [ and {
  
  
  • Removing closing pair on backspace on (, [ and {
  
  
  • Ctrl + 2 + sl (sl comes from 'split lines' -- can be used to add a new line after each comma in the selection
  
  
  • Ctrl + 2 + is (is comes from 'import string' -- can be used to transform the selected import into a string with dots
  
  
  
  


• General:
  
  
  
  • Code-completion properly working on relative import with an alias
  
  
  • Fixed racing issue that could deadlock pydev (under really hard to reproduce circumstances)
  
  
  • Removing reloading code while debugging until (if) it becomes more mature in the python side
  
  
  • Fixed issue where a new project created didn't have the source folder correctly set
  
  
  • Text selection in double click no longer has weird behavior
  
  
  • Local refactoring working on files not in the PYTHONPATH
  
  
  • Edit properly working on string substitution variables
  
  
  • Using with statement on python 2.5 no longer makes lines wrong in the AST
  
  
  
  

Playing around with Ordered Dictionary (collections.OrderedDict)

The new and cool feature added to Python 3.1.x family is the Ordered Dictionary. Some implementations have been lying around for sometime, it's good to see one made it into  the Python standard library.

Dictionaries are general purpose container data structure that are accessed through keys. It uses a hashing mechanism to achieve fast retrieval of information by key on typical cases. The annoying thing about standard dictionary dict object is that, whenever we retrieve the keys, it is not guaranteed to be sorted.
In Java platform, usually this dictionary is called map. java.util.Map provides interface to implementations of map such as java.util.HashMap, java.util.TreeMap.

Every value is associated with value, written in : pair.

Try to paste this code to your Python 3.1 interpreter:

[sourcecode lang="python"]<br />ud = dict()<br />ud['c']='1'<br />ud['b']='2'<br />ud['a']='3'<br />[/sourcecode]

This interactive session below highlight the thing:

[sourcecode lang="shell"]<br />>>> ud = dict()<br />>>> ud['c']='1'<br />>>> ud['b']='2'<br />>>> ud['a']='3'<br />>>> ud<br />{'a': '3', 'c': '1', 'b': '2'}<br />[/sourcecode]

Nice general purpose container for all of our applications. The dictionary keys doesn't display in sorted order.

Instead when we paste this code into Python interpreter:

[sourcecode lang="python"]<br />import collections as coll<br />od = coll.OrderedDict()<br />od['c']='1'<br />od['b']='2'<br />od['a']='3'<br />[/sourcecode]

We will get this result:

[sourcecode lang="shell"]<br />>>> import collections as coll<br />>>> od = coll.OrderedDict()<br />>>> od['c']='1'<br />>>> od['b']='2'<br />>>> od['a']='3'<br />>>> od<br />OrderedDict([('c', '1'), ('b', '2'), ('a', '3')])<br />[/sourcecode]

As we can see in the result above, the collections.OrderedDict objects displayed the keys according to the sequence that they were inserted. When an insertion done on an already existing key, the new insertion will overwrite the value but the sequence is left untouched. A deletion followed by addition will move the key to the end of the list, as show in the session below (continuation of the previous one).

[sourcecode lang="shell"]<br />>>> od['d']='4'<br />>>> od<br />OrderedDict([('c', '1'), ('b', '2'), ('a', '3'), ('d', '4')])<br />>>> od['b']='5'<br />>>> od<br />OrderedDict([('c', '1'), ('b', '5'), ('a', '3'), ('d', '4')])<br />>>> od.pop('a')<br />'3'<br />>>> od<br />OrderedDict([('c', '1'), ('b', '5'), ('d', '4')])<br />>>> od['a']='6'<br />>>> od<br />OrderedDict([('c', '1'), ('b', '5'), ('d', '4'), ('a', '6')])<br />>>><br />[/sourcecode]

I guess "battery included" still holds, or probably, "more organised battery included...".
Hooray for Python.

Python 3.1.2 Released (bug fix released)

Python 3.1.2 (bugfix release) is out now! We can download from this site: http://www.python.org/download/

Spring Python 1.1.0.M1 Released

SpringSource has has just announced last  week of a milestone release of SpringPython 1.1.0.M1. This announcement made aware about this project. There is a project that has nearly reached its 1.1 version that tries to develop Spring-like framework in Python. I would like to look into this project.

It is different from invoking Spring Java from Jython in  that, this project brings the concept of Spring framework into the CPython platform in general. Some of the configuration are really Pythonic!

I think I will explore more on this project.

Setting Up Your Own Jython 2.5.1 Environment

In this post I'll show you how to setup your own Jython environment.

Prerequisite to this, you must have a Java Runtime Environment (JRE) installed in your system. Chances are when you already have browser running some Java applet or Java Web Start application, you already have JRE installed on your system.
Get the latest JRE from http://java.com/en/download/manual.jsp.

First you need to download a Jython binaries installer, currently the latest one is version 2.5.1, which you could download from this link.

After download completion you should have a file named jython_installer-2.5.1.jar, click on the file, or run from command line:

[sourcecode lang="shell"]<br />$ java -jar jython_installer-2.5.1.jar<br />[/sourcecode]

Or in some other platform:

[sourcecode lang="shell"]<br />c:\&gt; java -jar jython_installer-2.5.1.jar<br />[/sourcecode]

Now you need to add you Jython path to your OS Path variable, so that the shell or command line interpreter is able to find Jython. In my sample Windows installation case:

[sourcecode lang="shell"]<br />C:\&gt; set PATH=%PATH%;c:\opt\env\jython2.5.1<br />[/sourcecode]

Alternatively, if you are running bash shell (assuming you installed Jython to /opt/env/jython2.5.1 folder):

[sourcecode lang="shell"]<br />$ export PATH=$PATH:/opt/env/jython2.5.1<br />[/sourcecode]

Now you may proceed with the first invocation of Jython.

[sourcecode lang="shell"]<br />C:\&gt; jython<br />*sys-package-mgr*: processing new jar, 'C:\opt\env\jython2.5.1\jython.jar'<br />*sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\resources.jar'<br />*sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\rt.jar'<br />*sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\jsse.jar'<br />*sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\jce.jar'<br />*sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\charsets.jar'<br />*sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\ext\dnsns.jar'<br />*sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\ext\localedata.jar'<br />*sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\ext\QTJava.zip'<br />*sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\ext\sunjce_provider.jar'<br />*sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\ext\sunmscapi.jar'<br />*sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\ext\sunpkcs11.jar'<br />Jython 2.5.1 (Release_2_5_1:6813, Sep 26 2009, 13:47:54)<br />[Java HotSpot(TM) Client VM (Sun Microsystems Inc.)] on java1.6.0_16<br />Type "help", "copyright", "credits" or "license" for more information.<br />&gt;&gt;&gt;<br />[/sourcecode]

The jython command line actually invoked a Windows batch file jython.bat, which
When first time invoked, Jython interpreter will activate sys-package-mgr to add standard Java library classes as Python package.

 

After the installation, just play around with simple thing such as:

[sourcecode lang="shell"]<br />Jython 2.5.1 (Release_2_5_1:6813, Sep 26 2009, 13:47:54)<br />[Java HotSpot(TM) Client VM (Sun Microsystems Inc.)] on java1.6.0_16<br />Type "help", "copyright", "credits" or "license" for more information.<br />&gt;&gt;&gt; from java.lang import System<br />&gt;&gt;&gt; System.out.println(&amp;quot;Hello, world!&amp;quot;)<br />Hello, world!<br />&gt;&gt;&gt; System.out.println('Hello, world!')<br />Hello, world!<br />&gt;&gt;&gt; System.currentTimeMillis()<br />1257145977410L<br />&gt;&gt;&gt; from java.lang import String<br />&gt;&gt;&gt; s = String(&amp;quot;abc&amp;quot;)<br />&gt;&gt;&gt; s.toString()<br />u'abc'<br />[/sourcecode]

Look at how System.out.println is able to receive both single quote and double quote Python string, and also the java.lang.String type by a Java class method is a Unicode string (u'abc').

PyDev 1.5 on Eclipse Galileo 3.5 SR1

I begin to have more time to explore the Eclipse Galileo Service Release 1 (Eclipse 3.5.1). This time I want to set it up for my Python development, using the PyDev plugin.

PyDev is an Eclipse plugin for Python language application development. It supports CPython, Jython and IronPython runtimes. It supports the interactive as well as non-interactive Python development on Eclipse IDE.

Eclipse IDE (and platform) has become the de facto industry standard IDE. More and more free software, open source software, and proprietary software makers build their systems on Eclipse platform. Galileo is the codename for 3.5 release, and now the latest one is the SR1 (Service Release 1).

There has been interesting development on PyDev since its last 1.4.7 version. PyDev has moved to be sheltered under the umbrella of Aptana. PyDev and PyDev Extension now has been merged and both now open source (previously the PyDev Extension, the advanced version of PyDev was not an open source).

The update site has been moved from domain www.fabioz.com (http://www.fabioz.com/pydev) to domain pydev.org (http://pydev.org/updates) . Aptana  This development looks good for me, means that PyDev now being maintained by its own organization, and hopefully in more serious efforts.

In Eclipse Galileo, you need to go to the menu and choose: Help > Install New Software...

It will show the Install dialog.

Click the [Add] button on the upper of menu dialog. You will get the "Add Site" dialog.

Type name and location.
Name: "PyDev Update  Site" (you can feel with any arbitrary name though)
Location: http://pydev.org/updates

Back to the "Install" dialog, the previous "Add Site" will fill up the "Work with" field for you.

Now tick the Checkbox "PyDev for Eclipse" under "PyDev". You may also optionally tick the "Pydev Mylyn Integration". In this example we don't tick.

Click the [Next >] button. It will show you the Install Details:

Proceed by clicking [Next >] button. Review Licenses dialog will be displayed.

Click the radio button "I accept the terms of the license  agreement" when you are agree with the licenses. Proceed by clicking [Finish] button.

You will see the progress bar. Somewhere around the progress, you will be asked whether to install software that contains unsigned content.

Click [OK] to proceed (we have no choice as long as the provider of this plugin hasn't signed the content).

Click the [Yes] button to restart your Eclipse IDE.

Chardet Python Library: Determining Character Encoding of Text File or Text Stream

Recently I have came into a disagreement with fellow programmer. He tried to create view simple codes in different programming languageshe knows: C, C++, Perl, Python, PHP, and Java (I think it's for self-actualization, obviously not for money or wealth). It turns out to be he created XML parser codes on those (programming) languages.

The code doesn't produce as expected, except of course in Python. He ascertained that it is because most those languages make use of libxml2 library (from GNU). He came into a conclusion that the Java library might also make use of the libxml2 library from GNU, which I believe most unlikely. Java wouldn't normally pick GNU stuffs for its library. It really hit into my Java developer pride, and I need to prove that it is not the library that is incorrect, instead the input file is not correctly encoded.

Although in Western world most text files usually play along well most of the time, characters other than ordinary characters will be displayed incorrectly. Most of the case it will be displayed incorrectly in countries that uses special characters!

Since the first time I work in Singapore, I absorb it quickly that the ability to display these special characters are one important thing a web application should have, especially when they cater for the Asian market! You will see that they will require you to do i18n, display this in Traditional Chinese characters, in Simplified Chinese characters, Tamil characters, Thai characters, to name a few...

It brought me to this question:
If I have an arbitrary text file, how could I know which encoding the text uses?

I googled around and found  this: Universal Encoding Detector (chardet) library. The chardet site shows how to do it for web sites.

[sourcecode lang="python"]<br />&gt;&gt;&gt; import urllib<br />&gt;&gt;&gt; urlread = lambda url: urllib.urlopen(url).read()<br />&gt;&gt;&gt; import chardet<br />&gt;&gt;&gt; chardet.detect(urlread("http://google.cn/"))<br />{'encoding': 'GB2312', 'confidence': 0.99}<br /><br />&gt;&gt;&gt; chardet.detect(urlread("http://yahoo.co.jp/"))<br />{'encoding': 'EUC-JP', 'confidence': 0.99}<br />[/sourcecode]

Now it here comes the next question for me: if it is not a web site, but a file instead, how to detect the encoding?

So here is the solution:

[sourcecode lang="python"]<br />&gt;&gt;&gt; import chardet<br />&gt;&gt;&gt; fileread = lambda filename: open(filename, "r").read()<br />&gt;&gt;&gt; chardet.detect(fileread("italian-english.xml"))<br />{'confidence': 0.9899999999999999, 'encoding': 'utf-8'}<br /><br />&gt;&gt;&gt; chardet.detect(fileread("utf8_demo.txt"))<br />{'confidence': 0.9899999999999999, 'encoding': 'utf-8'}<br /><br />[/sourcecode]

So this way, I checked that the text file is most likely an UTF-8 encoded text.

By the way, the encoding detection engine library was derived from (or ported from) Mozilla auto-detection code, which has been widely used. So more or less I believe it is mature and powerful enough for most usages.

Another thing to note is that those codes above are using lambda notation, a feature of Python language borrowed from pure functional programming syntax.

Python 3.1 File I/O open() Is No Longer Binary Mode By Default

After long holiday on my wedding preparation, D day and honeymoon, I returned back in shape.

Some things happened during the off days, such as the acquisition of SpringSource by VMWare, Inc.

I try to run my piece of XML parsing code like this in Python 3.1:

[sourcecode lang="python"]
import xml.parsers.expat
import sys
import os.path

filename = "companies.xml"
parser = xml.parsers.expat.ParserCreate()
f = open(filename, "r")
parser.ParseFile(f)
f.close()
[/sourcecode]

The code above throws an error like this:

[sourcecode lang="shell"]
TypeError: read() did not return a bytes object (type=str)
[/sourcecode]

This source code works in Python 2.6, but failed when running on Python 3.1.

After comparing the manual for the built-in open() function between those 2 versions (2.6 and 3.x versions), I found out that there is a new feature in Python 3.x which is not backward compatibility (unlike transitions between 2.x versions, the transition from 2.x to 3.x may break the backward compatibility).

Python 3.x added the "t" for text, "b" for binary, "+" for updating (read/write) and "U" modifier to the open file mode.

It turns out to be that Python 3.1 no more handles file open as binary by default.Now the text ("t") mode become default for Python 3.1 meanwhile Python 2.6 assume all file access are binary accesses. Python 3.x has implemented modes of more similarity to its C stdio library counterpart than its previous 2.6 version.

Since Python 3.x added additional parameter to the open() function, we must now specify "b" to make it binary access, so that the read() method will return bytes, otherwise it will return str.

[sourcecode lang="python"]
import xml.parsers.expat
import sys
import os.path

xmlFilename = "companies.xml"
p = xml.parsers.expat.ParserCreate()
f = open(xmlFilename, "rb")
p.ParseFile(f)
f.close()
[/sourcecode]

Now the ParseFile() method get what it asks for, a file handler with read() method that return bytes instead of str.

PyDev 1.4.7 on Eclipse Galileo

WARNING:

The content of this blog is obsolete now, as newer PyDev version 1.5 has been released. Please look at my latest blog post on this.

I begin to have more time to explore the Eclipse Galileo (3.5) again. This time I want to set it up for my Python development, using the PyDev plugin. Current PyDev plugin version is 1.4.7

Assuming you already have a working  installation of Galileo, and have opened a workspace.

The update site for PyDev is http://pydev.sourceforge.net/updates

In Galileo, you need choose: Help > Install New Software...

[caption id="attachment_605" align="aligncenter" width="313" caption="Adding the PyDev Plugin to Eclipse Galileo"][/caption]

The "Install" dialog will show up.



Click on the [Add] button at the top right of dialog. You should see this "Add Site" dialog.

Type in the data.

Name: Py Dev Update Site
Location: http://www.fabioz.com/pydev/



Click [OK] button.


Tick the checkbox "PyDev for Eclipse" under "PyDev". Click [Next >] button.


Click [Next >].



Click the radio button "I accept the terms of the license agreement" when you agree. Click [Finish] button.

You will see the progress bar.



On completion of the installation process, Eclipse will ask you whether you want to restart.

Answer by clicking the [Yes] button.

Done.

Python's Lazy Evaluation on Exception Handling

I tried a simple code like this:

[sourcecode lang="python"]
try:
while True:
print('yipee')
except KeyboardInterrupt:
print('w00t')
[/sourcecode]

It runs successfully on command line interface, and keeps printing "yipee" until the user press Ctrl-C. After that I did a typo, which turns out to mistype the "KeyboardInterrupt" as "KeybaordInterrupt".

[sourcecode lang="python"]
try:
while True:
print('yipee')
except KeybaordInterrupt:
print('w00t')
[/sourcecode]

To my surprise, it still runs well, it keeps printing "yipee" to the screen. It's just that
when I press Ctrl-C, Python threw this error:

[sourcecode lang="shell"]
Traceback (most recent call last):
File '<stdin>', line 3, in <module>
KeyboardInterrupt
[/sourcecode]

During handling of the above exception, another exception occurred:

[sourcecode lang="shell"]
Traceback (most recent call last):
File '<stdin>', line 4, in <module>
NameError: name 'KeybaordInterrupt' is not defined
[/sourcecode]

I looked at the documentation of Python 3.1 which says:
The try statement works as follows.

First, the try clause (the statement(s) between the try and except keywords) is executed.

• If no exception occurs, the except clause is skipped and execution of the try statement is finished.


• If an exception occurs during execution of the try clause, the rest of the clause is skipped. Then if its type matches the exception named after the except keyword, the except clause is executed, and then execution continues after the try statement.


• If an exception occurs which does not match the exception named in the except clause, it is passed on to outer try statements; if no handler is found, it is an unhandled exception and execution stops with a message as shown above.

The exception handling in Python works in a lazy manner, they will only validate the except clauses just before processing the exception!