TypeError: Cannot create a consistent method resolution order (MRO) for bases object

[digitalorganics@gmail.com]

What are the reason one would get this error: TypeError: Cannot create
a consistent method resolution order (MRO) for bases object ??

I can provide the code if needed....

[Simon Forman]

Re: TypeError: Cannot create a consistent method resolution order (MRO) for bases object

digitalorganics @gmail.com wrote:[color=blue]
> What are the reason one would get this error: TypeError: Cannot create
> a consistent method resolution order (MRO) for bases object ??
>
> I can provide the code if needed....[/color]

Yes, do that.

That's an amazing error.

~Simon

[Terry Reedy]

Re: TypeError: Cannot create a consistent method resolution order(MRO)for bases object


<digitalorganic s@gmail.com> wrote in message
news:1151345197 .691600.200060@ y41g2000cwy.goo glegroups.com.. .[color=blue]
> What are the reason one would get this error: TypeError: Cannot create
> a consistent method resolution order (MRO) for bases object ??[/color]

Because the interpreter cannot ;-)
[color=blue]
> I can provide the code if needed....[/color]

Details beget details ;-)
Yes, the class statement (header line up to ':') that bombed and the same
(first line) for classes it inherits from (and their base classes). The
conflict should be in the latter.

tjr

[digitalorganics@gmail.com]

Re: TypeError: Cannot create a consistent method resolution order (MRO) for bases object

Hint: If I change Dog and Bat to old-style classes, there's no problem,
everything works fine.


Okay, here's the code dump from my playground::
------------------------------------------
#!/usr/bin/env python

class Mixin:
def mixin(object, *classes):
NewClass = type('Mixin', (object.__class __,) + classes, {})
newobj = NewClass()
newobj.__dict__ .update(object. __dict__)
return newobj

class Cat(object):
def __init__(self):
self.love = 0
def meow(self):
print "meow"
class Dog(object):
def bark(self):
print "bark"
class Bat(object):
def scream(self):
print "scream"

mycat = Cat()
mycat.love = 4
mycat.__class__ .__bases__ += (Mixin,)
mycat.mixin(Dog , Bat)
print mycat.love

def isClass(object) :
if isinstance(obje ct, type):
return True
elif isinstance(obje ct, types.ClassType ):
return True
else:
return False

def listClasses():
classes = []
for eachobj in globals().keys( ):
if isClass(globals ()[eachobj]):
classes.append( globals()[eachobj])
print eachobj
return classes

def applyMixinGloba l(*Mixins):
for eachclass in listClasses():
MixInto(eachcla ss, Mixins)
#applyMixinGlob al(Mixin)

def MixInto(Class, *Mixins):
for eachMixin in Mixins:
if eachMixin not in Class.__bases__ :
Class.__bases__ += (eachMixin,)
MixInto(Bat, Mixin)
Bat.__bases__ += (Dog,)
dargo = Bat()
dargo = dargo.mixin(Cat )
dargo.meow()

Simon Forman wrote:[color=blue]
> digitalorganics @gmail.com wrote:[color=green]
> > What are the reason one would get this error: TypeError: Cannot create
> > a consistent method resolution order (MRO) for bases object ??
> >
> > I can provide the code if needed....[/color]
>
> Yes, do that.
>
> That's an amazing error.
>
> ~Simon[/color]

[digitalorganics@gmail.com]

Re: TypeError: Cannot create a consistent method resolution order (MRO)for bases object

Oh, I forgot the line that bombed, sorry:

line 52, in __main__
Bat.__bases__ += (Dog,)
TypeError: Cannot create a consistent method resolution
order (MRO) for bases object, Mixin, Dog

See my other post for the complete code and my relevant note about
new-style classes, thanks...

Terry Reedy wrote:[color=blue]
> <digitalorganic s@gmail.com> wrote in message
> news:1151345197 .691600.200060@ y41g2000cwy.goo glegroups.com.. .[color=green]
> > What are the reason one would get this error: TypeError: Cannot create
> > a consistent method resolution order (MRO) for bases object ??[/color]
>
> Because the interpreter cannot ;-)
>[color=green]
> > I can provide the code if needed....[/color]
>
> Details beget details ;-)
> Yes, the class statement (header line up to ':') that bombed and the same
> (first line) for classes it inherits from (and their base classes). The
> conflict should be in the latter.
>
> tjr[/color]

[Maric Michaud]

Re: TypeError: Cannot create a consistent method resolution order(MRO) for bases object

Le lundi 26 juin 2006 20:06, digitalorganics @gmail.com a écrit :[color=blue]
> What are the reason one would get this error: TypeError: Cannot create
> a consistent method resolution order (MRO) for bases object ??
>
> I can provide the code if needed....[/color]
This is the python solution to the diamond problem (cf. wikipedia).

In [61]: class a(object) : pass
....:
In [62]: class b(a) : pass
....:
In [63]: class c(object, a) : pass
....:
---------------------------------------------------------------------------
exceptions.Type Error Traceback (most recent
call last)

/home/maric/<ipython console>

TypeError: Error when calling the metaclass bases
Cannot create a consistent method resolution
order (MRO) for bases object, a

In [64]: b.mro()
Out[64]: [<class '__main__.b'>, <class '__main__.a'>, <type 'object'>]

In [65]: class c(a, object) : pass
....:

In [66]: c.mro()
Out[66]: [<class '__main__.c'>, <class '__main__.a'>, <type 'object'>]

In [67]: class d(b, c) : pass
....:

In [69]: d.mro()
Out[69]:
[<class '__main__.d'>,
<class '__main__.b'>,
<class '__main__.c'>,
<class '__main__.a'>,
<type 'object'>]

mro means "method resolution order", this is the path the interpreter will
look for attributes for a given class. You cannot introduce inconsistency in
this path, for example duplicate the type object before another type (or any
type wich appear to be the ancestor of another).

--
_____________

Maric Michaud
_____________

Aristote - www.aristote.info
3 place des tapis
69004 Lyon
Tel: +33 426 880 097

[digitalorganics@gmail.com]

Re: TypeError: Cannot create a consistent method resolution order (MRO) for bases object


Maric Michaud wrote:[color=blue]
> Le lundi 26 juin 2006 20:06, digitalorganics @gmail.com a écrit :[color=green]
> > What are the reason one would get this error: TypeError: Cannot create
> > a consistent method resolution order (MRO) for bases object ??
> >
> > I can provide the code if needed....[/color]
> This is the python solution to the diamond problem (cf. wikipedia).
>
> In [61]: class a(object) : pass
> ....:
> In [62]: class b(a) : pass
> ....:
> In [63]: class c(object, a) : pass
> ....:
> ---------------------------------------------------------------------------
> exceptions.Type Error Traceback (most recent
> call last)
>
> /home/maric/<ipython console>
>
> TypeError: Error when calling the metaclass bases
> Cannot create a consistent method resolution
> order (MRO) for bases object, a
>
> In [64]: b.mro()
> Out[64]: [<class '__main__.b'>, <class '__main__.a'>, <type 'object'>]
>
> In [65]: class c(a, object) : pass
> ....:
>
> In [66]: c.mro()
> Out[66]: [<class '__main__.c'>, <class '__main__.a'>, <type 'object'>]
>
> In [67]: class d(b, c) : pass
> ....:
>
> In [69]: d.mro()
> Out[69]:
> [<class '__main__.d'>,
> <class '__main__.b'>,
> <class '__main__.c'>,
> <class '__main__.a'>,
> <type 'object'>]
>
> mro means "method resolution order", this is the path the interpreter will
> look for attributes for a given class. You cannot introduce inconsistencyin
> this path, for example duplicate the type object before another type (or any
> type wich appear to be the ancestor of another).
>
> --[/color]

Ah, thank you Maric, I see the problem. I diagrammed the flow of class
inheritance and I can see the problem clearly. Ruby doesn't have this
problem because it uses a single inheritance model complemented by the
power of mixins (modules of functionality mixed into classes as
needed). So what's the Pythonic solution to this problem?

[Steve Holden]

Re: TypeError: Cannot create a consistent method resolution order(MRO) for bases object

digitalorganics @gmail.com wrote:[color=blue]
> Maric Michaud wrote:
>[color=green]
>>Le lundi 26 juin 2006 20:06, digitalorganics @gmail.com a écrit :
>>[color=darkred]
>>>What are the reason one would get this error: TypeError: Cannot create
>>>a consistent method resolution order (MRO) for bases object ??
>>>
>>>I can provide the code if needed....[/color]
>>
>>This is the python solution to the diamond problem (cf. wikipedia).
>>
>>In [61]: class a(object) : pass
>> ....:
>>In [62]: class b(a) : pass
>> ....:
>>In [63]: class c(object, a) : pass
>> ....:
>>---------------------------------------------------------------------------
>>exceptions.Ty peError Traceback (most recent
>>call last)
>>
>>/home/maric/<ipython console>
>>
>>TypeError: Error when calling the metaclass bases
>> Cannot create a consistent method resolution
>>order (MRO) for bases object, a
>>
>>In [64]: b.mro()
>>Out[64]: [<class '__main__.b'>, <class '__main__.a'>, <type 'object'>]
>>
>>In [65]: class c(a, object) : pass
>> ....:
>>
>>In [66]: c.mro()
>>Out[66]: [<class '__main__.c'>, <class '__main__.a'>, <type 'object'>]
>>
>>In [67]: class d(b, c) : pass
>> ....:
>>
>>In [69]: d.mro()
>>Out[69]:
>>[<class '__main__.d'>,
>> <class '__main__.b'>,
>> <class '__main__.c'>,
>> <class '__main__.a'>,
>> <type 'object'>]
>>
>>mro means "method resolution order", this is the path the interpreter will
>>look for attributes for a given class. You cannot introduce inconsistency in
>>this path, for example duplicate the type object before another type (or any
>>type wich appear to be the ancestor of another).
>>
>>--[/color]
>
>
> Ah, thank you Maric, I see the problem. I diagrammed the flow of class
> inheritance and I can see the problem clearly. Ruby doesn't have this
> problem because it uses a single inheritance model complemented by the
> power of mixins (modules of functionality mixed into classes as
> needed). So what's the Pythonic solution to this problem?
>[/color]
Technically, wait until Python 3.0. Until then, just make sure all your
classes inherit from (something that inherits from ...) object.

regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Love me, love my blog http://holdenweb.blogspot.com
Recent Ramblings http://del.icio.us/steve.holden

[Michele Simionato]

Re: TypeError: Cannot create a consistent method resolution order (MRO) for bases object

digitalorganics @gmail.com wrote:[color=blue]
> What are the reason one would get this error: TypeError: Cannot create
> a consistent method resolution order (MRO) for bases object ??[/color]

See http://www.python.org/download/releases/2.3/mro/

Michele Simionato