weird behavior wrapping global functions into classes

[Alex Martelli]

"Les Schaffer" <schaffer at optonline.net> wrote in message
news:0cahit44sql68p8pd2qgt59f600neha687 at 4ax.com...
> been losing sleep over this one...
>
> why does the following code successfully wrap the built-in open function
> into a class, but shelve's open method gets incorrectly (??) taken as an
> instance method? notice that everything works fine for the Flat version,

Whenever a function is accessed as an attribute of a class or
instance (and in the latter case, it's found in the class and
not in the instance itself), it's transmuted into a method
(unbound and bound, respectively).  So, if you do need a callable
to NOT have  method behavior, wrap the function in a non-function
callable; cfr., e.g.:
http://aspn.activestate.com/ASPN/Python/Cookbook/Recipe/52304
for more discussion, but it boils down to:

class Callable:
    def __init__(self, anycallable):
        self.thecallable = anycallable
    def __call__(self, *args, **kwds):
        return self.thecallable(*args, **kwds)

and

> class NumFlat(NumStorage):
>     mode = 'w'
>     DB = 'flat.txt'
>     #db = open(DB, mode)
>     dbopen=open

change the last line into
      dbopen = Callable(open)


Alex