Class decorators do not inherit properly
bruno.42.desthuilliers at wtf.websiteburo.oops.com
Fri Jul 13 09:52:59 CEST 2007
Chris Fonnesbeck a écrit :
> I have a class that does MCMC sampling (Python 2.5) that uses decorators
> -- one in particular called _add_to_post that appends the output of the
> decorated method to a class attribute.
> However, when I
> subclass this base class, the decorator no longer works:
> Traceback (most recent call last):
> File "/Users/chris/Projects/CMR/closed.py", line 132, in <module>
> class M0(MetropolisHastings):
> File "/Users/chris/Projects/CMR/closed.py", line 173, in M0
> NameError: name '_add_to_post' is not defined
> yet, when I look at the dict of the subclass (here called M0), I see the
> decorator method:
> In : dir(M0)
> I dont see what the problem is here -- perhaps someone could shed
> some light. I thought it might be the underscore preceding the name,
> but I tried getting rid of it and that did not help.
A minimal runnable code snippet reproducing the problem would *really*
help, you know...
Anyway: the body of a class statement is it's own namespace. So in the
body of your base class, once the _add_to_post function is defined, you
can use it. But when subclassing, the subclass's class statement creates
a new namespace, in which _add_to_post is not defined - hence the
NameError. To access this symbol, you need to use a qualified name, ie:
# code here
Now there may be better solutions, but it's hard to tell without knowing
more about your concrete use case.
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