Alternative iterator syntax

[Michael Hudson]

aahz at panix.com (Aahz Maruch) writes:

> In article <mailman.982769240.31345.python-list at python.org>,
> Huaiyu Zhu  <hzhu at users.sourceforge.net> wrote:
> >
> >  [...]
> 
> I'm not sure where to put this question, so I'm just deleting all of
> Huaiyu's text.
> 
> How does one get UserDict.keys (note: no parens here) to return an
> iterator?  Normally this will simply return a reference to the method.

class _Keys:
   def __init__(self, dict):
       self.dict = dict
   def __contains__(self, item):
       return self.dict.has_key(item)
   def __call__(self):
       return self.dict.keys()
   ... etc ...

class UserDict:
    def __init__(self, dict=None):
        if data is None:
            data = {}
        self.data = dict
        self.keys = _Keys(dict)
        ... etc ...

Not *very* different from how you'd implement this in C, really.

Hmm, you might want to have the _Keys object hang on the instance
rather than the dict if assigning to the .data member of UserDict is
allowed.  Which would create a circular reference, but we don't have
to worry about that too much now...

Cheers,
M.

-- 
  > Look I don't know.  Thankyou everyone for arguing me round in
  > circles.  
  No need for thanks, ma'am; that's what we're here for.
                                    -- LNR & Michael M Mason, cam.misc