metaclasses

[castironpi]

What are metaclasses?

 

[Daniel Fetchinson]

What are metaclasses?

http://www.google.com/search?q=python+metaclass

HTH,
Daniel

 

[castironpi]

http://www.google.com/search?q=python+metaclass

HTH,
Daniel

Not satisfied.

http://en.wikipedia.org/wiki/Metaclass#Python_example

That's a limitation. The constructor can omit the superclass call,
but it can't have keyword arguments, and can't use
AttributeInitType.__call__ with positionals. Subclass
AttributeInition, decorate __init__, or decorate class.

 

[Benjamin]

What are metaclasses?

Depends on whether you want to be confused or not. If you do, look at
this old but still head bursting essay: http://www.python.org/doc/essays/metaclasses/.

Basically, the metaclass of a (new-style) class is responsible for
creating the class. This means when Python sees
class Foo(object):
__metaclass__ = FooMeta
class FooMeta(type):
def __new__(cls, name, bases, dct):
#do something cool to the class
pass
It asks FooMeta to create the class Foo. Metaclasses always extend
type because type is the default metaclass.

 

[castironpi]

Depends on whether you want to be confused or not. If you do, look at
this old but still head bursting essay:http://www.python.org/doc/essays/metaclasses/.

Basically, the metaclass of a (new-style) class is responsible for
creating the class. This means when Python sees
class Foo(object):
    __metaclass__ = FooMeta
class FooMeta(type):
    def __new__(cls, name, bases, dct):
       #do something cool to the class
       pass
It asks FooMeta to create the class Foo. Metaclasses always extend
type because type is the default metaclass.

But you can stack class decorations, but not class metas.

@somethingcool1
@somethingcool2
class Foo:
pass

* class Foo:
__metaclass__= MetaCool1, MetaCool

* denotes malformed

 

[Gerard Flanagan]

But you can stack class decorations, but not class metas.

@somethingcool1
@somethingcool2
class Foo:
pass

* class Foo:
__metaclass__= MetaCool1, MetaCool

* denotes malformed

-----------------------
class Meta1(type):

def foo1(cls):
print 'hello'

class Meta2(type):

def foo2(cls):
print 'castiron'

class Meta(Meta1, Meta2):
pass

class Base(object):
__metaclass__ = Meta


Base.foo1()
Base.foo2()

 

[castironpi]

-----------------------
class Meta1(type):

    def foo1(cls):
        print 'hello'

class Meta2(type):

    def foo2(cls):
        print 'castiron'

class Meta(Meta1, Meta2):
    pass

class Base(object):
    __metaclass__ = Meta

Base.foo1()
Base.foo2()

class Base(object):
__metaclass__= type( 'Meta', ( Meta1, Meta2 ), {} )