object oriented inheritance problem

[Matthew Thorley]

I am trying to inherit from ElementTree so I can add some methods. This
is the code I am trying to make work, and the following is the error I
am getting.

from elementtree import ElementTree
class AcidTree(ElementTree):
def write_string(self):
....

File "/home/hope/var/proj/acid/server/mgacparse.py", line 22, in ?
class AcidTree(ElementTree):
TypeError: Error when calling the metaclass bases
module.__init__() takes at most 2 arguments (3 given)


I have *no* idea what is going on here. AcidTree does not implement an
__init__. It just adds two simple methods, which aren't even being
called when then exception is thrown. The exception occurs on the class
definition line when I try to inherit from ElementTree.

I looked around, and read some stuff in the python cook book, and
everything I've seen indicates that it should just work. My only thought
is that its a 'oldstyle' vs 'newstyle' classes issue. I know that
elementtree was written to be compatible with python 1.5 so maybe it
doesn't work with the new stuff. But thats just a crazy assumption I
made up to make myself feel better.

If anyone could please exmplain what my problem *really* is I would
appreciate it greatly. Thanks very much.

-Matthew

 

[Michele Simionato]

It looks like ElementTree is a module and not a class.
The same error message was posted here few weeks ago.
Actually, I discuss it in my Oxford lectures, page 30:
see
http://www.reportlab.org/~andy/accu2005/pyuk2005_simionato_wondersofpython.zip

(there also everything you want to know about new-style
classes and more).

Michele Simionato

 

[Fredrik Lundh]

I am trying to inherit from ElementTree so I can add some methods. This
is the code I am trying to make work, and the following is the error I
am getting.

from elementtree import ElementTree
class AcidTree(ElementTree):
def write_string(self):
....

File "/home/hope/var/proj/acid/server/mgacparse.py", line 22, in ?
class AcidTree(ElementTree):
TypeError: Error when calling the metaclass bases
module.__init__() takes at most 2 arguments (3 given)

I have *no* idea what is going on here.

note that you're trying to inherit from a module. the error message could
need some work...

something like

from elementtree.ElementTree import ElementTree, tostring

class AcidTree(ElementTree):
def write_string(self):
return tostring(self)

should work better.

</F>

 

[Matthew Thorley]

So is elementtree a module of modules? I didn't know you could do that.
I just assumed that from elementtree import ElementTree imported a class
from the module elementtree.

It works now. Thanks guys.

 

[Fredrik Lundh]

So is elementtree a module of modules? I didn't know you could do that.

"elementtree" is a package. see:

http://docs.python.org/tut/node8.html#SECTION008400000000000000000

for a bit more information.

</F>