Create a web site by Google App Engine

http://moma.appspot.com
Coming soon! haha!

Google App Engine:
http://code.google.com/appengine/

python class method

>>> class SomeClass(object):
... total = 0
... @classmethod
... def GetTotal(cls):
... return cls.total
... @classmethod
... def Add(cls, num):
... cls.total = cls.total + num
...
>>>
>>> A = SomeClass()
>>> B = SomeClass()
>>>
>>> A.GetTotal()
0
>>> B.Add(10)
>>> A.GetTotal()
10
>>> B.GetTotal()
10

Usage of grep

grep [OPTION] PATTERN [FILE]

Example:
Count for lines contain numbers:
grep -E '[0-9]+' -c filename

-E means extended regular expression
-c means to print a count of matching lines per file, otherwise it will print all suitable lines.

How to remove a file whose name starts with a - (minus)

use one of these commands:
rm -- -foo

rm ./-foo

How to lock screen in Ubuntu?

Ctrl + Alt + L

Singleton in Python

We don't need Singleton in Python. We need singleton just because we need some static data and static functions. In Python we can simply use following code:

def InitStaticData(data):
pass

class Global(object):
""" A global class to store static data."""
__private_data = xxx
static_data = InitStaticData(__private_data) //assume it's a list.


def ReadStaticData(arg):
return Global.StaticData[arg]

The Global class itself will be initialized for one time. And we can define related static function in the module. The only thing we should do is: do not use __init__ of Global.

Keep in mind: in Python, each module is itself an object without having to define an explicit class.

An abbreviation for Delivery

How about Dlvry?

How to check your disk quota under Linux

df --help

Usage of CAST in SQL

CAST( Var AS Type)
e.g.
Select CAST(1 AS Boolean);
true
Select CAST("123" AS INT);
123