Problem with sub-classing

[Bernard Lebel]

Hello,

I have this problem when subclassing classes where I get this error:

Traceback (most recent call last):

File "<Script Block >", line 344, in BBExportElement Granules_Execut e
from bb_pipeline import bb_exportelemen tgranules

File "\\Linuxserver\ ANIMATION\XSI\W ORKGROUP_ANIMAT ION\Data\Script s\bb_pipeline\b b_exportelement granules.py",
line 101, in ?
oWriter = bbExportGranule s()

File "\\Linuxserver\ ANIMATION\XSI\W ORKGROUP_ANIMAT ION\Data\Script s\bb_pipeline\b b_granules\bb_g ranuleexport\bb _granuleexport_ element.py",
line 73, in __init__
bbExportMeta.__ init__( self )

TypeError: unbound method __init__() must be called with bbExportMeta
instance as first argument (got bbExportGranule s instance instead)
- [line 343 in
\\Linuxserver\A NIMATION\XSI\WO RKGROUP_ANIMATI ON\plugins\bb_p ipeline\bb_pipe line_py.py]


In normal English:

I have class bbExportGranule s
bbExportGranule s is a sub-class of 6 other classes
In the __init__() of bbExportGranule s class, I call the __init__() of
5 of these super-classes.


The init of bbExportGranule s:

class bbExportGranule s( bbExportMeta, bbExportCluster s,
bbExportMateria ls, bbExportKinemat ics, bbExportModels, bbExportMetaToc
):

def __init__( self ):

bbExportMeta.__ init__( self )
bbExportCluster s.__init__( self )
bbExportMateria ls.__init__( self )
bbExportKinemat ics.__init__( self )
bbExportModels. __init__( self )


And the bbExportMeta class (the error is raised when bbExportGranule s
is subclassing that one):

class bbExportMeta:

def __init__( self ):

self.iPreviousA ssetVersion = gec.iNOPREVIOUS ASSETVERSION
self.iCurrentAs setVersion = gec.iMINCURRENT ASSETVERSION
self.sPreviousA ssetProject = xsi.getdefaultp roject()




Any suggestion? I really, really don't see what I'm doing wrong here,
especially that it actually used to work!



Thanks
Bernard

[Peter Otten]

Re: Problem with sub-classing

Bernard Lebel wrote:

Hello,
>
I have this problem when subclassing classes where I get this error:
>
Traceback (most recent call last):
>
File "<Script Block >", line 344, in BBExportElement Granules_Execut e
from bb_pipeline import bb_exportelemen tgranules
>
File
>

"\\Linuxserver\ ANIMATION\XSI\W ORKGROUP_ANIMAT ION\Data\Script s\bb_pipeline\b b_exportelement granules.py",

line 101, in ?
oWriter = bbExportGranule s()
>
File
>

"\\Linuxserver\ ANIMATION\XSI\W ORKGROUP_ANIMAT ION\Data\Script s\bb_pipeline\b b_granules\bb_g ranuleexport\bb _granuleexport_ element.py",

line 73, in __init__
bbExportMeta.__ init__( self )
>
TypeError: unbound method __init__() must be called with bbExportMeta
instance as first argument (got bbExportGranule s instance instead)
- [line 343 in
>

\\Linuxserver\A NIMATION\XSI\WO RKGROUP_ANIMATI ON\plugins\bb_p ipeline\bb_pipe line_py.py]

>
>
In normal English:
>
I have class bbExportGranule s
bbExportGranule s is a sub-class of 6 other classes
In the __init__() of bbExportGranule s class, I call the __init__() of
5 of these super-classes.
>
>
The init of bbExportGranule s:
>
class bbExportGranule s( bbExportMeta, bbExportCluster s,
bbExportMateria ls, bbExportKinemat ics, bbExportModels, bbExportMetaToc
):
>
def __init__( self ):
>
bbExportMeta.__ init__( self )
bbExportCluster s.__init__( self )
bbExportMateria ls.__init__( self )
bbExportKinemat ics.__init__( self )
bbExportModels. __init__( self )
>
>
And the bbExportMeta class (the error is raised when bbExportGranule s
is subclassing that one):
>
class bbExportMeta:
>
def __init__( self ):
>
self.iPreviousA ssetVersion = gec.iNOPREVIOUS ASSETVERSION
self.iCurrentAs setVersion = gec.iMINCURRENT ASSETVERSION
self.sPreviousA ssetProject = xsi.getdefaultp roject()
>
>
>
>
Any suggestion? I really, really don't see what I'm doing wrong here,
especially that it actually used to work!

Change bbExportGranule s to

class bbExportGranule s( bbExportMeta, bbExportCluster s,
bbExportMateria ls, bbExportKinemat ics, bbExportModels, bbExportMetaToc
):
        
        def __init__(self, bbExportMeta=bb ExportMeta): # the only change
                
                bbExportMeta.__ init__( self )
                bbExportCluster s.__init__( self )
                bbExportMateria ls.__init__( self )
                bbExportKinemat ics.__init__( self )
                bbExportModels. __init__( self )

If it then starts to work again you are probably rebinding bbExportMeta
later in your script, e. g:

>>class A:

.... def method(self): pass
....

>>class B(A):

.... def method(self):
.... A.method(self)
....

>>b = B()
>>b.method() # no error
>>class A: # rebinding A

.... def method(self): pass
....

>>b.method() # oops

Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 3, in method
TypeError: unbound method method() must be called with A instance as first
argument (got B instance instead)

One way to make that happen is to import the same file twice, once as part
of a package and once directly. Solution: never set a path into a
package...

Peter

[Bernard Lebel]

Re: Problem with sub-classing

Okay, that make sense.

Now the question is: regarding the re-binding behavior, is this
actually problematic? By that I mean that is it good coding practice
to avoid this issue altogether as much as possible, or is it okay to
live with it if you use the __init__ argument trick you have shown?


Thanks
Bernard



On 7/17/06, Peter Otten <__peter__@web. dewrote:

Bernard Lebel wrote:
>

Hello,

I have this problem when subclassing classes where I get this error:

Traceback (most recent call last):

File "<Script Block >", line 344, in BBExportElement Granules_Execut e
from bb_pipeline import bb_exportelemen tgranules

File

"\\Linuxserver\ ANIMATION\XSI\W ORKGROUP_ANIMAT ION\Data\Script s\bb_pipeline\b b_exportelement granules.py",

line 101, in ?
oWriter = bbExportGranule s()

File

"\\Linuxserver\ ANIMATION\XSI\W ORKGROUP_ANIMAT ION\Data\Script s\bb_pipeline\b b_granules\bb_g ranuleexport\bb _granuleexport_ element.py",

line 73, in __init__
bbExportMeta.__ init__( self )

TypeError: unbound method __init__() must be called with bbExportMeta
instance as first argument (got bbExportGranule s instance instead)
- [line 343 in

\\Linuxserver\A NIMATION\XSI\WO RKGROUP_ANIMATI ON\plugins\bb_p ipeline\bb_pipe line_py.py]

In normal English:

I have class bbExportGranule s
bbExportGranule s is a sub-class of 6 other classes
In the __init__() of bbExportGranule s class, I call the __init__() of
5 of these super-classes.


The init of bbExportGranule s:

class bbExportGranule s( bbExportMeta, bbExportCluster s,
bbExportMateria ls, bbExportKinemat ics, bbExportModels, bbExportMetaToc
):

def __init__( self ):

bbExportMeta.__ init__( self )
bbExportCluster s.__init__( self )
bbExportMateria ls.__init__( self )
bbExportKinemat ics.__init__( self )
bbExportModels. __init__( self )


And the bbExportMeta class (the error is raised when bbExportGranule s
is subclassing that one):

class bbExportMeta:

def __init__( self ):

self.iPreviousA ssetVersion = gec.iNOPREVIOUS ASSETVERSION
self.iCurrentAs setVersion = gec.iMINCURRENT ASSETVERSION
self.sPreviousA ssetProject = xsi.getdefaultp roject()




Any suggestion? I really, really don't see what I'm doing wrong here,
especially that it actually used to work!

>
Change bbExportGranule s to
>
class bbExportGranule s( bbExportMeta, bbExportCluster s,
bbExportMateria ls, bbExportKinemat ics, bbExportModels, bbExportMetaToc
):
>
def __init__(self, bbExportMeta=bb ExportMeta): # the only change
>
bbExportMeta.__ init__( self )
bbExportCluster s.__init__( self )
bbExportMateria ls.__init__( self )
bbExportKinemat ics.__init__( self )
bbExportModels. __init__( self )
>
If it then starts to work again you are probably rebinding bbExportMeta
later in your script, e. g:
>

>class A:

... def method(self): pass
...

>class B(A):

... def method(self):
... A.method(self)
...

>b = B()
>b.method() # no error
>class A: # rebinding A

... def method(self): pass
...

>b.method() # oops

Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 3, in method
TypeError: unbound method method() must be called with A instance as first
argument (got B instance instead)
>
One way to make that happen is to import the same file twice, once as part
of a package and once directly. Solution: never set a path into a
package...
>
Peter
>
--

http://mail.python.org/mailman/listinfo/python-list

>

[Peter Otten]

Re: Problem with sub-classing

Bernard Lebel wrote:

Okay, that make sense.
>
Now the question is: regarding the re-binding behavior, is this
actually problematic? By that I mean that is it good coding practice
to avoid this issue altogether as much as possible, or is it okay to
live with it if you use the __init__ argument trick you have shown?

I suggested the "argument trick" for diagnosis only.

One /good/ coding practice is to choose descriptive names for (toplevel)
objects. Another is to avoid

from module import *

style imports which tend to be the most common source of name clashes.


Peter