Metaclass' __init__ Does not Initialize

[achan]

As I was trying to create a metaclass, I found out that __init__ defined in
it does not initializes at all:

class CMeta(type):
def __new__(cls, ClassName, BaseClass, ClassDict):
def __init__(self):
for k in self.__slots__:
k = 'something'
NewDict = {'__slots__': [], '__init__': __init__}
for k in ClassDict:
if k.startswith('_ _') and k.endswith('__' ):
if k in NewDict:
warnings.warn(" Can't set attr %r in bunch-class %r" %
(k, ClassName))
else:
NewDict[k] = ClassDict[k]
else:
NewDict['__slots__'].append(k)
return type.__new__(cl s, ClassName, BaseClass, NewDict)

class CNewType(object ):
__metaclass__ = CMeta
a = 'nothing'
b = 'nothing'
c = 'nothing'


[color=blue][color=green][color=darkred]
>>> x = CNewType()[/color][/color][/color]
something
something
something[color=blue][color=green][color=darkred]
>>> x.a[/color][/color][/color]
Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
AttributeError: a ------------->>> Non-existent!






class CMeta(type):
def __new__(klass, name, base, dict):
def __init__(self):
for s in seq:
s = 123
print s
newDict = {'__init__': __init__, seq = []}
return type.__new__(kl ass, name, base, newDict)

class Test(object):
__metaclass__: CMeta

[color=blue][color=green][color=darkred]
>>> a = Test()
>>>[/color][/color][/color]

[Stephan Diehl]

Re: Metaclass' __init__ Does not Initialize

The __init__ runs just fine.
You just did a tiny little programming error
The line that says
"k = 'something'"
must be replaced by
"setattr(self,k ,'something')"

Stephan

achan wrote:
[color=blue]
> As I was trying to create a metaclass, I found out that __init__ defined
> in it does not initializes at all:
>
> class CMeta(type):
> def __new__(cls, ClassName, BaseClass, ClassDict):
> def __init__(self):
> for k in self.__slots__:
> k = 'something'
> NewDict = {'__slots__': [], '__init__': __init__}
> for k in ClassDict:
> if k.startswith('_ _') and k.endswith('__' ):
> if k in NewDict:
> warnings.warn(" Can't set attr %r in bunch-class %r" %
> (k, ClassName))
> else:
> NewDict[k] = ClassDict[k]
> else:
> NewDict['__slots__'].append(k)
> return type.__new__(cl s, ClassName, BaseClass, NewDict)
>
> class CNewType(object ):
> __metaclass__ = CMeta
> a = 'nothing'
> b = 'nothing'
> c = 'nothing'
>
>
>[color=green][color=darkred]
>>>> x = CNewType()[/color][/color]
> something
> something
> something[color=green][color=darkred]
>>>> x.a[/color][/color]
> Traceback (most recent call last):
> File "<interacti ve input>", line 1, in ?
> AttributeError: a ------------->>> Non-existent!
>
>
>
>
>
>
> class CMeta(type):
> def __new__(klass, name, base, dict):
> def __init__(self):
> for s in seq:
> s = 123
> print s
> newDict = {'__init__': __init__, seq = []}
> return type.__new__(kl ass, name, base, newDict)
>
> class Test(object):
> __metaclass__: CMeta
>
>[color=green][color=darkred]
>>>> a = Test()
>>>>[/color][/color][/color]

[Alex Martelli]

Re: Metaclass' __init__ Does not Initialize

achan wrote:
[color=blue]
> As I was trying to create a metaclass, I found out that __init__ defined
> in it does not initializes at all:[/color]
...[color=blue]
> def __init__(self):
> for k in self.__slots__:
> k = 'something'[/color]

Haven't looked at the rest of your code, but this part can't possibly
be right -- you're just rebinding local variable k over and over,
uselessly. Perhaps you want the loop's body to be
setattr(self, k, 'something')
....?


Alex

[Michele Simionato]

Re: Metaclass' __init__ Does not Initialize

"achan" <anabell@sh163. net> wrote in message news:<mailman.6 49.1068611151.7 02.python-list@python.org >...[color=blue]
> As I was trying to create a metaclass, I found out that __init__ defined in
> it does not initializes at all <snip>[/color]

1. Please, test your attempts before posting, it would be helpful for
you as for the people who try to understand you.

2. Are you sure you want __slots__? 99.9% of times __slot__ are not needed,
I never use them, and I would rather NOT have this feature available
from Python (yes if available from C) since it is an endless cause
of confusion.

3. Here is an example of a working metaclass with an __init__ as you
want:

class CMeta(type):
def __new__(mcl, name, bases, dic):
def __init__(self):
for s in self.seq:
print s
newDict = {'__init__': __init__, 'seq' : [123]}
return super(CMeta,mcl ).__new__(mcl, name, bases, newDict)

class Test(object):
__metaclass__= CMeta

a = Test() #=> 123


You may figure out for yourself your mistakes.

Michele Simionato