A.T.Hofkamp wrote:
> Hello all,
>
> This morning I tried to create my own read-only dictionary, and failed
> miserably.
> I don't understand why, can somebody enlighten me?
>
> Below is a brute-force experiment that cannot deal with "x in obj", plz read
> the explanation below the code:
> --------------------------------
> class myowndict(object):
> def __init__(self, mydict):
> self.mydict = mydict
>
> # Below is produced with
> # print '\n'.join([' self.%s = self.mydict.%s' % (v,v)
> # for v in dir(dict)])
> # commented-out functions done by hand
> #
> #self.__class__ = self.mydict.__class__
> self.__cmp__ = self.mydict.__cmp__
> self.__contains__ = self.mydict.__contains__
> self.__delattr__ = self.mydict.__delattr__
> self.__delitem__ = self.mydict.__delitem__
> #self.__doc__ = self.mydict.__doc__
> self.__eq__ = self.mydict.__eq__
> self.__ge__ = self.mydict.__ge__
> self.__getattribute__ = self.mydict.__getattribute__
> self.__getitem__ = self.mydict.__getitem__
> self.__gt__ = self.mydict.__gt__
> self.__hash__ = self.mydict.__hash__
> #self.__init__ = self.mydict.__init__
> self.__iter__ = self.mydict.__iter__
> self.__le__ = self.mydict.__le__
> self.__len__ = self.mydict.__len__
> self.__lt__ = self.mydict.__lt__
> self.__ne__ = self.mydict.__ne__
> #self.__new__ = self.mydict.__new__
> self.__reduce__ = self.mydict.__reduce__
> self.__reduce_ex__ = self.mydict.__reduce_ex__
> self.__repr__ = self.mydict.__repr__
> self.__setattr__ = self.mydict.__setattr__
> self.__setitem__ = self.mydict.__setitem__
> self.__str__ = self.mydict.__str__
> self.clear = self.mydict.clear
> self.copy = self.mydict.copy
> self.fromkeys = self.mydict.fromkeys
> self.get = self.mydict.get
> self.has_key = self.mydict.has_key
> self.items = self.mydict.items
> self.iteritems = self.mydict.iteritems
> self.iterkeys = self.mydict.iterkeys
> self.itervalues = self.mydict.itervalues
> self.keys = self.mydict.keys
> self.pop = self.mydict.pop
> self.popitem = self.mydict.popitem
> self.setdefault = self.mydict.setdefault
> self.update = self.mydict.update
> self.values = self.mydict.values
>
> # end of __init__
>
> if __name__ == '__main__':
> fd = myowndict({1:10})
> print 1 in fd # FAILS! (with "TypeError: iterable argument required")
> --------------------------------
>
> I wanted to make my own dictionary. However, a simple element test failed
> (after implementing various __*__ functions), and I cannot figure out why.
>
> The above code is a brute force attempt, where I forward all methods (except
> __class__, __doc__, __init__, and __new__) to my local 'mydict' object.
>
> IT STILL FAILS.
>
> So if copying all methods of a native dictionary is not enough, what should I
> do to make my class work as a dictionary WITHOUT deriving from dict (which
> will
> obviously work).
>
You have to overwrite the "__new__" method to return an object of your
new type.
regards
Steve
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