for in sequence problem... possible new operator to add to python

Sean Ross sross at connectmail.carleton.ca
Thu Jul 10 19:03:35 CEST 2003


"Adam Gent" <agentgt at yahoo.com> wrote in message
news:3a8fc6c5.0307100816.634c83a3 at posting.google.com...
> I was fooling around subclassing a dictionary object and noticed that
> when
> I do the standard "for in <object-is-a-sequence>:" that I have no
> control on how python gets that sequence.
[snip]
> However I want b to be the values with out doing:
> for b in bl.values()

You can do it as follows:

class Blah(dict):
    def __iter__(self):
        return iter(self.values())

b = Blah()
b.update({'hello':'world', 'how':'are', 'you':'today'})
for v in b:
    print v

# OUTPUT:
# are
# today
# world

Just be aware that you are introducing surprising behaviour - other Python
programmers will expect

for v in b:

to iterate thru the keys of b, not the values. It's up to you whether you
want this behaviour more than you want your code to be easily understood.







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