Posted By: akdom
How would one create an iterative function (or iterator object) in python?
Iterator objects in python conform to the iterator protocol, which basically means they provide two methods:
__iter__returns the iterator object and is implicitly called
at the start of loops.
__next__()method returns the next value and is implicitly called at each loop increment. This method raises a StopIteration exception when there are no more value to return, which is implicitly captured by looping constructs to stop iterating.
Here’s a simple example of a counter:
class Counter: def __init__(self, low, high): self.current = low - 1 self.high = high def __iter__(self): return self def __next__(self): # Python 2: def next(self) self.current += 1 if self.current < self.high: return self.current raise StopIteration for c in Counter(3, 9): print(c)
This will print:
3 4 5 6 7 8
This is easier to write using a generator, as covered in a previous answer:
def counter(low, high): current = low while current < high: yield current current += 1 for c in counter(3, 9): print(c)
The printed output will be the same. Under the hood, the generator object supports the iterator protocol and does something roughly similar to the class Counter.
David Mertz’s article, Iterators and Simple Generators, is a pretty good introduction.