Python standard library --- Built-in Functions (2)

callable(object) : return true if the object appears callable, false if not. If the object is callable, it's still possible a call fails. If not, calling object will never succeed. Classes are callable, but class instances are not callable except that the class has a method __call__().

>>> callable(bool)

True

>>> callable(True)

False

>>> c =bool()

>>> c

False

>>> callable(c)

False

>>> class demo:

...     def __call__(self):

...             print 1

... 

>>> callable(demo)

True

>>> d=demo()

>>> callable(d)

True

>>> class demo2:

...     def __index__(self):

...             print 2

... 

>>> e=demo2()

>>> callable(e)

False

>>> 

chr(i) : change an integer i to one character who ascii code is the integer, i must be in [0..255], Likely, unichr will change the integer to a unicode character.

On the opposite, ord(char) will change one character to an integer.

>>> chr(97)

'a'

>>> ord('a')

97

>>> ord("a")

97

>>> unichr(97)

u'a'

classmethod(function) ; like an attribute to decorate a function,  the first argument must be an instance itself. It can be called dm.cm(2,3) or dm1.cm(2,3)

It's a little like extension method. If you use dm.cm(2,3), it will translate into dm.cm(dm(),2,3), if you use dm1.cm(2,3), it will translate into dm1.cm(dm1,2,3)

>>> class demo:

...     @classmethod

...     def cm(cls,arg1,arg2):

...             print cls.v+arg1+arg2

...     v=1

... 

>>> demo.cm(2,4)

7

>>> d=demo()

>>> d.cm(2,3)

6

>>> 

cmp(x,y) : compare the two objects x and y and return an integer, if x<y return negative value, if x==y return zero, else return positive value.

>>> cmp('a','b')

-1

>>> cmp('a','a')

0

>>> cmp('b','a')

1

>>> 

------------------------
Kind Regards,
Yonggang Meng