Python Django Metaclass working

Python Django Metaclass working

* Not creating any object of class 'Test'.

class MyMetaClass(type):
def __new__(meta, classname, bases, classDict):
print "\n--------MyMetaClass-------__new__-----"
    print '\nmeta:---------', meta
    print '\nClass Name:---------', classname
    print '\nBases:---------', bases
    print '\nClass Attributes:---------', classDict
    return type.__new__(meta, classname, bases, classDict)

def __init__(cls, *arg):
print "\n--------MyMetaClass-------__init__-----", arg
print "\n--------MyMetaClass-------cls---------", cls
print "\n--------MyMetaClass-------dir(cls)---------", dir(cls)


class BaseCls(object):
def __init__(self, *arg):
print "\n--------BaseCls-------__init__-----", arg

def base_cls_method(self):
print "\n--------BaseCls-------basecls_method-----"


class Test(BaseCls):
__metaclass__ = MyMetaClass
#methods in this class are passed into the metaclass 'MyMetaClass' as functions.

def __init__(self, *arg):
self.number = arg
#member datas in this class are not passed into the metaclass.
print "\n--------Test-------__init__-----", arg
print "\n--------Test-------self---------", self
print "\n--------Test-------dir(self)---------", dir(self)

def test_method(self):
print "\n--------Test-------test_method-----"


OUTPUT
=======

root@saju-laptop:~/Desktop# python aa.py

--------MyMetaClass-------__new__-----

meta:---------

Class Name:--------- Test

Bases:--------- (,)

Class Attributes:--------- {'__module__': '__main__', '__metaclass__': , '__init__': ,
'test_method': }

--------MyMetaClass-------__init__----- ('Test', (,), {'__module__': '__main__',
'__metaclass__': , '__init__': , 'test_method': })

--------MyMetaClass-------cls---------

--------MyMetaClass-------dir(cls)---------  ['__class__', '__delattr__', '__dict__',
'__doc__', '__format__',  '__getattribute__', '__hash__', '__init__', '__metaclass__', 
'__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__',  '__setattr__',
'__sizeof__', '__str__', '__subclasshook__',  '__weakref__', 'base_cls_method', 'test_method']


=============================== 2

* Creating an object of class 'Test'.
* Here Special class method '__new__' in the metaclass 'MyMetaClass' return an object.

class MyMetaClass(type):
def __new__(meta, classname, bases, classDict):
print "\n--------MyMetaClass-------__new__-----"
    print '\nmeta:---------', meta
    print '\nClass Name:---------', classname
    print '\nBases:---------', bases
    print '\nClass Attributes:---------', classDict
    return type.__new__(meta, classname, bases, classDict)

def __init__(cls, *arg):
print "\n--------MyMetaClass-------__init__-----", arg
print "\n--------MyMetaClass-------cls---------", cls
print "\n--------MyMetaClass-------dir(cls)---------", dir(cls)


class BaseCls(object):
def __init__(self, *arg):
print "\n--------BaseCls-------__init__-----", arg

def base_cls_method(self):
print "\n--------BaseCls-------basecls_method-----"


class Test(BaseCls):
__metaclass__ = MyMetaClass
#methods in this class are passed into the metaclass 'MyMetaClass' as functions.

def __init__(self, *arg):
self.number = arg
#member datas in this class are not passed into the metaclass.
print "\n--------Test-------__init__-----", arg
print "\n--------Test-------self---------", self
print "\n--------Test-------dir(self)---------", dir(self)

def test_method(self):
print "\n--------Test-------test_method-----"


print "\n-------Test()------",Test(5000)



OUTPUT
========

root@saju-laptop:~/Desktop# python aa.py

--------MyMetaClass-------__new__-----

meta:---------

Class Name:--------- Test

Bases:--------- (,)

Class Attributes:--------- {'__module__': '__main__', '__metaclass__': , '__init__': ,
'test_method': }

--------MyMetaClass-------__init__----- ('Test', (,), {'__module__': '__main__',
'__metaclass__': , '__init__': , 'test_method': })

--------MyMetaClass-------cls---------

--------MyMetaClass-------dir(cls)---------  ['__class__', '__delattr__', '__dict__',
'__doc__', '__format__',  '__getattribute__', '__hash__', '__init__', '__metaclass__', 
'__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__',  '__setattr__',
'__sizeof__', '__str__', '__subclasshook__',  '__weakref__', 'base_cls_method', 'test_method']

-------Test()------
--------Test-------__init__----- (5000,)

--------Test-------self--------- <__main__.test>

--------Test-------dir(self)---------  ['__class__', '__delattr__', '__dict__',
'__doc__', '__format__',  '__getattribute__', '__hash__', '__init__', '__metaclass__', 
'__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__',  '__setattr__',
'__sizeof__', '__str__', '__subclasshook__',  '__weakref__', 'base_cls_method', 'number',
'test_method']
<__main__.test>


=============================== 3

* Creating an object of class 'Test'.
* Here Special class method '__new__' in the metaclass 'MyMetaClass' not return anything.

class MyMetaClass(type):
def __new__(meta, classname, bases, classDict):
print "\n--------MyMetaClass-------__new__-----"
    print '\nmeta:---------', meta
    print '\nClass Name:---------', classname
    print '\nBases:---------', bases
    print '\nClass Attributes:---------', classDict

def __init__(cls, *arg):
print "\n--------MyMetaClass-------__init__-----", arg
print "\n--------MyMetaClass-------cls---------", cls
print "\n--------MyMetaClass-------dir(cls)---------", dir(cls)


class BaseCls(object):
def __init__(self, *arg):
print "\n--------BaseCls-------__init__-----", arg

def base_cls_method(self):
print "\n--------BaseCls-------basecls_method-----"


class Test(BaseCls):
__metaclass__ = MyMetaClass
#methods in this class are passed into the metaclass 'MyMetaClass' as functions.

def __init__(self, *arg):
self.number = arg
#member datas in this class are not passed into the metaclass.
print "\n--------Test-------__init__-----", arg
print "\n--------Test-------self---------", self
print "\n--------Test-------dir(self)---------", dir(self)

def test_method(self):
print "\n--------Test-------test_method-----"


print "\n-------Test()------",Test(5000)


OUTPUT
========

root@saju-laptop:~/Desktop# python aa.py

--------MyMetaClass-------__new__-----

meta:---------

Class Name:--------- Test

Bases:--------- (,)

Class Attributes:--------- {'__module__': '__main__', '__metaclass__': , '__init__': ,
'test_method': }

-------Test()------
Traceback (most recent call last):
File "aa.py", line 40, in
print "\n-------Test()------",Test(5000)
TypeError: 'NoneType' object is not callable


http://www.voidspace.org.uk/python/articles/metaclasses.shtml
http://stackoverflow.com/questions/100003/what-is-a-metaclass-in-python

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