defcon logo post iconHere is something for all you hackers out there reading my blog: all the videos from the previous year's biggest and greatest hacker conference -- DefCon 15!

I found these videos via this post on Roy/SAC's blog. He bought a full set of DVDs for several hundred dollars and uploaded them to Google Video! I sincerely appreciate his effort!

Total of more than 200 videos!

For your convenience, here is the full DefCon 15 session listing:
Download Full DefCon 15 Session Listing (.pdf).

You're welcome to comment here on lectures you found intriguing and liked the most!

Have fun!

This article is part of the article series "Musical Geek Friday."
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The Eternal Flame, God Wrote in Lisp SongThis week on Musical Geek Friday - God Wrote in Lisp (also known as The Eternal Flame) song!

This song is written by Bob Kanefsky and is performed by Julia Ecklar. It's a parody of another song of hers - "God Lives on Terra".

The song is about a question which programming language God could have used to create us?

God had a tight 6 day deadline to create the world, so he had to make a smart decision which language to use. Some folks say that it could have been C++ or C, but these languages are out as God would not have been able to even count grains of sand with 32-bit integers! Others say it could have been Fortran, Java, COBOL or even APL. But we all know the truth...

God wrote the world in Lisp!

Here it is! The God Wrote in Lisp song:


Download this song: god wrote in lisp.mp3 (musical geek friday #5)
Downloaded: 39213 times

Download lyrics: god wrote in lisp lyrics (musical geek friday #5)
Downloaded: 6229

If you liked this song, it's included in a music CD "Roundworm" which contains parodies about Star Trek, dead cats, Lisp programming (this song), and everything in between!

Here is the lyrics of The Eternal Flame (God Wrote in Lisp) song:

I was taught assembler in my second year of school.
It's kinda like construction work — with a toothpick for a tool.
So when I made my senior year, I threw my code away,
And learned the way to program that I still prefer today.

Now, some folks on the Internet put their faith in C++.
They swear that it's so powerful, it's what God used for us.
And maybe it lets mortals dredge their objects from the C.
But I think that explains why only God can make a tree.

For God wrote in Lisp code
When he filled the leaves with green.
The fractal flowers and recursive roots:
The most lovely hack I've seen.
And when I ponder snowflakes, never finding two the same,
I know God likes a language with its own four-letter name.

Now, I've used a SUN under Unix, so I've seen what C can hold.
I've surfed for Perls, found what Fortran's for,
Got that Java stuff down cold.
Though the chance that I'd write COBOL code
is a SNOBOL's chance in Hell.
And I basically hate hieroglyphs, so I won't use APL.

Now, God must know all these languages, and a few I haven't named.
But the Lord made sure, when each sparrow falls,
that its flesh will be reclaimed.
And the Lord could not count grains of sand with a 32-bit word.
Who knows where we would go to if Lisp weren't what he preferred?

And God wrote in Lisp code
Every creature great and small.
Don't search the disk drive for man.c,
When the listing's on the wall.
And when I watch the lightning
Burn unbelievers to a crisp,
I know God had six days to work,
So he wrote it all in Lisp.

Yes, God had a deadline.
So he wrote it all in Lisp.

Download "God Wrote in Lisp" Song

Download this song: god wrote in lisp.mp3 (musical geek friday #5)
Downloaded: 39213 times

Download lyrics: god wrote in lisp lyrics (musical geek friday #5)
Downloaded: 6229

Click to listen:

Have fun and until next geeky Friday!

python design patterns video lecturesIn my previous post about learning Python programming through video lectures I stopped at three lectures on Design Patterns. This time I continue from there.

If you don't know what a Design Pattern is, think of it as a simple solution to a specific problem that occurs very frequently in software design.

For example, suppose you use a bunch of unrelated pieces of code. It is a nice idea to bring the unrelated pieces of code together in a unified interface. This design pattern is called Facade. There are a bunch of patterns like this one!

The three lectures are given by Alex Martelli who works as "Über Tech Lead" for Google.

Python Design Patterns, Part I

Alex briefly covers the history and main principles of Design Patterns and quickly moves to discussing Structural and Behavioral DPs in Python.

Interesting ideas from the lecture:

  • [03:24] The name "Design Patterns" was first used by Christopher Alexander, an architect, who abstracted the idea of building buildings as building them using well known patterns which can be applied to the same problem over and over again without ever doing it the same way twice.
  • [05:30] Design Patterns are mostly applied to Object Oriented programming because it's the most widely spread programming paradigm nowadays.
  • [08:36] Design Patterns are not invented, they are discovered.
  • [10:00] Alex says that the original book Design Patterns by the Gang of Four should be read only when you are a master of DPs.
  • [13:10] Three classical categories of DPs are - Creational (deal with object instantiaton), Structural (deal with composition of objects) and Behavioral (deal with interaction of objects).
  • [14:05] "Program to an interface, not to an implementation."
  • [17:00] Use inheritance only when absolutely necessary, otherwise use "hold or wrap" principle.
  • [18:30] Never have more than one dot - Law of Demeter.
  • [18:50] Inheritance cannot restrict, use wrapping to restrict.
  • [21:41] In most of the cases when you need a single instance of something in Python, use a module instead of a class.
  • [22:23] Otherwise, just make 1 instance (without enforcing one).
  • [22:59] Singleton is also called "Highlander".
  • [24:50] There is basically no way to support subclassing well in Singleton.
  • [25:45] Monostate is also called "Borg".
  • [27:00] Python's data overriding helps in Monostate Design Pattern.
  • [29:00] Each Python's type/class is essentially a factory.
  • [32:06] Python does a "two-phase object construction".
  • [35:30] Adapter Design Pattern (it tweaks the interface to your needs).
  • [41:22] Facade Design Pattern (it provides a simple subset of a complex functionality).
  • [47:25] Bridge Design Pattern (it abstracts interface from the implementation).
  • [49:30] Decorator Design Pattern (it transparently modifies some functionality.).
  • [50:24] Proxy Design Pattern (sounds the same as decorator just for access control).
  • [51:21] Q and A!

Python Design Patterns, Part II

In this lecture Alex discusses behavioral patterns. Unlike the first part, he goes in depth of some of the patterns and explains how they can be implemented in Python.

Interesting ideas from the lecture:

  • [02:25] Template Method is a great pattern with a lousy name, a better name is "self-delegation".
  • [03:43] Example of Template Method Design Pattern (text pagination).
  • [08:50] Template Method Rationale.
  • [09:45] The "Hollywood Principle" - "don't call us, we'll call you"
  • [12:05] In Python you can also override data.
  • [13:10] Example of Template Method in Queue.Queue.
  • [14:05] If you are a good Python programmer, use Queue in threaded applications.
  • [17:45] Customizing Queue.
  • [19:30] Example of Template Method in cmd.Cmd.cmdloop.
  • [21:22] Example of Template Method in asyncore.dispatcher.
  • [22:30] Variant of Template Method - Mixin (not presented in Gang of Four book). It's a class to be multiply-inherited from and supplies organizing methods only.
  • [25:50] Template Method in DictMixin class.
  • [26:45] Example of DictMixin usage.
  • [29:00] Hooks can be factored out in another class. Two examples of this from Python's stdlib are HTML's formatter vs. writer, SAX's parser vs. handler
  • [32:40] Hook method introspection example of cmd.Cmd.docmd.
  • [33:30] There are three kinds of Template Methods - plain, factored into separate classes, and introspective.
  • [34:35] Example of all three kinds of Template Methods used in unittest.TestCase.
  • [36:17] State and Strategy Design Patterns. Very similar classes in what they do. They both factor out object's behavior.
  • [40:40] Ring buffer example done via State Design Pattern.
  • [43:35] Q and A!

Python Design Patterns, A Recap

This video lecture was presented at Google Developers day. It is a short version of the previous two video lectures. It starts with an example of Facade Design Pattern, moves on to history and all the types of design patterns.

I did not write out the interesting moments from this lecture as it was a subset of previous two lectures.

If you liked these lectures, check out this geek song about another commonly used design pattern - Model-View-Controller Song :)

Even though these were Python design patterns, to understand some of them I used Perl Design Patterns website!

Were there any interesting points in the lectures that caught your attention?

This article is part of the article series "Musical Geek Friday."
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model view controller mvc musical geek friday songThis week on Musical Geek Friday - the Model View Controller (MVC) song!

This song was written and performed by James Dempsey, an engineer at Apple. James says that he searched iTunes for a model-view-controller song but there was none, so he wrote his own song about this topic.

The song is about a particular Design Pattern in software engineering. A Design Pattern is a simple solution to a specific problem that occurs very frequently in software design. The MVC Design Pattern was first discovered and described by Smalltalk people (see the original paper). This key idea of this pattern is that it decouples data to be displayed (model) from the code displaying the data (view) and code receiving user input (controller).

Here it the Model View Controller song:


Download this song: model-view-controller song.mp3 (musical geek friday #4)
Downloaded: 41859 times

Download lyrics: model-view-controller lyrics (musical geek friday #4)
Downloaded: 6092

Talking about the MVC design pattern in this song, Ralph Johnson on squeak's mailing list comments:

The problem is that the song is NOT about Smalltalk MVC. In this song, the controller is a layer between the view and the model, which usually means it is a mediator. The song also says that the controller is copying values from one field to another, which also indicates that it is a mediator. However, in true MVC, the controller is a strategy for handling events. The events come directly to it, rather than to the view. The controller changes the model, but it is not notified by the model. When the user presses a key or moves the mouse, the controller receives the event. It checks with the view to map mouse locations into model coordinates, then interacts directly with the model. If it changes the model then the model notifies all dependents (observers), which notifes the view, which redisplays.

The song desribes Ivar Jacobson's Model/Interface/Control, in which the Control is responsible for an entire use case. It is not MVC. Jacobson's model is like the MVC model, but his Interface is a combination of View and Controller and his Control is not at all like a real Controller.

Here is the lyrics of MVC song:

Model View, Model View, Model View Controller
MVC's the paradigm for factoring your code,
into functional segments so your brain does not explode.
To achieve reusability you gotta keep those boundaries clean,
Model on the one side, View on the other, the Controller's in between.

Model View - It's got three layers like Oreos do.
Model View creamy Controller

Model objects represent your applications raison d'tre.
Custom classes that contain data logic and et cetra.
You create custom classes in your app's problem domain,
then you can choose to reuse them with all the views,
but the model objects stay the same.

You can model a throttle in a manifold,
Model level two year old.
Model a bottle of fine Chardonnay.
Model all the twaddle stuff people say.
Model the coddle in a boiling eggs.
Model the waddle in Hexley's legs.

One, two, three, four.
Model View - You can model all the models that pose for GQ.
Model View Controller

View objects tend to be controls that view and edit,
Cocoa's got a lot of those, well written to its credit.
Take an NSTextView, hand it any old Unicode string,
the user interacts with it, it can hold most anything.
But the view don't knows about the Model:
That string could be a phone number or the words of Aristotle.
Keep the coupling loose and so achieve a massive level of reuse.

Model View - All rendered very nicely in Aqua blue
Model View Controller

You're probably wondering now.
You're probably wondering how,
the data flows between Model and View.
The Controller has to mediate,
between each layer's changing state,
to synchronize the data of the two.
It pulls and pushes every changed value.

Model View - mad props to the smalltalk crew!
for Model View Controller

Model View - it's pronouced Oh Oh not Uh Uh
Model View Controller

There's a bit more on this story,
a few more miles upon this road,
well nobody seems to get much glory
writing controller code.
Well the model is mission critical
and gorgeous is the view,
But I'm not being lazy, but sometimes it's just crazy
how much code i write is just glue.
And it wouldn't be so tragic,
but the code ain't doing magic:
it's just moving values through.
And I wish I had a dime
for every single time
I set a TextField's stringValue.

Model View - how we're gonna deep-six all that glue
Model View Controller

Controller's know the Model and View very
uahh - intimately
They often are hardcoding
which is very verboten for reusability.
But now you can connect any value you select
to any view property.
And I think you'll start binding,
then you'll be finding less code in your source tree.
Yeah I know I was astounded,
that's not even a rhyme.

But I think it bares repeating
all the code you won't be needing,
when you hook it up in IB.

Model View - it even handles multiple selections too
Model View Controller

Model View - hope I get my G5 before you
Model View Controller

Yeah, yeah, yeah. Yeah.

I also found a video of James singing it live on WWDC 2003. Here is the video:

Download "Model View Controller" Song

Download this song: model-view-controller song.mp3 (musical geek friday #4)
Downloaded: 41859 times

Download lyrics: model-view-controller lyrics (musical geek friday #4)
Downloaded: 6092

Click to listen:

Have fun and until next geeky Friday!

PS. One of my next posts will be on Design Patterns in Python, so check back!

introduction to sqlite database rdbmsIf you have been following my blog, you might have noticed that almost all of my projects use the SQLite database engine.

My projects are relatively tiny, low traffic and data is mostly queried, not written. Such characteristics make SQLite the perfect database for my projects.

If you did not know, the SQLite database is self contained within a single file! There are no configuration woes, no network security to worry about, no hundreds pages of documentation. It's just a single file!

See Distinctive Features of SQLite and Appropriate Uses for SQLite pages to find other points when SQLite is a good fit and when not.

Here is the lecture by Richard Hipp, the author of SQLite:

Here are some interesting facts from the lecture:

  • [02:50] SQLite is designed to be embedded, it's less than 250 KB in size.
  • [08:00] Uncommon SQLite uses (this got me most interested): stand-in for client-server DBMS during testing/debugging. Local database caching. Implementing complex data structures. Sorting large amounts of data. Configuration files. IPC via database. Application file formats.
  • [14:06] SQLite is very convenient to use as a tool to teach basics of SQL, as it just works.
  • [19:32] Unusual features of SQLite: SQLite ignores data types for columns (you can store string in an integer column, for example). SQLite does type affinity on data inserted in columns. Table 'sqlite_master' stores information about tables. Attaching to multiple databases simultaneously via ATTACH command. You can join or copy across multiple open databases (for example, hot backup the database).
  • [24:40] Anatomy of an SQL database engine.
  • [27:00] SQLite compiles queries to byte code (can be viewed via EXPLAIN statement) to be executed in a virtual machine.
  • [28:20] Observations of SQLite: trouble with licensing. A register based virtual machine is much easier to generate code for which is optimal than a stack based VM. Dynamic typing in databases is a really good thing. Regression tests allow rewriting large parts of SQLite without minor version releases.
  • [36:30] Q and A!
  • [36:35] Is there ORM tool available for SQLite?
  • [39:30] How is dynamic typing better than static typing in databases?
  • [41:32] What did you mean by 'complex data types'?
  • [43:15] Why is a register based virtual machine better than a stack based?
  • [44:22] Why does SQLite only parse foreign keys but not enforce them?
  • [46:08] Is SQLite an in-memory database?
  • [46:50] What's the future of SQLite?
  • [48:10] My SQLite DB got corrupt, what do I do?
  • [49:30] When does the DB roll back in case of power failure?
  • [50:30] What happens if there is a second power failure while rolling back the queries from previous power failure?

A few notes from me.

The usage of 'manifest typing' really confused me in this lecture, because I, and most of the people I have talked to, uses this term for 'static typing'. The author of SQLite uses it to mean 'dynamic typing'. Don't know why...

An SQLite database can be managed via the sqlite (or sqlite3) command line tool or GUI tool such as SQLite Browser (primitive), SQLiteSpy (advanced) and SQLite Manager (as a FireFox Add-on).

Finally, here are a few articles you should read if you are interested in more advanced SQLite details:

I hope you enjoyed it and have fun using SQLite for your next project!