parameterized iterator?

Raymond Hettinger vze4rx4y at verizon.net
Wed Feb 19 23:59:09 CET 2003


"Fortepianissimo" wrote
> Just occurs to me that if I can somehow pass in an argument to specify
> a special ordering when traversing a tree, that'll be perfect.

Python's own solution to this problem is to use a different method
for each type of iterator:

mydict.itervalues()
mydict.iteritems()
mydict.iterkeys()

Alternatively, you can create a method with a parameter.
Don't use __iter__() for this since it is already defined with
no parameters; instead, try something like: traverse(ordering).
Using generators are a clean way to return an iterator whose next()
method obeys the ordering:

class Tree:
    . . .
    def traverse(order):
        "Untested psuedocode approximation of what you want"
        if order == INORDER:
             self.left.traverse(order)
             yield self.value
             self.right.traverse(order)
        elif order == PREORDER:
             yield self.value
             self.left.traverse(order)
             self.right.traverse(order)
        . . .


Raymond Hettinger






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