Iterators in Python are objects that you can retrieve other objects from, one by one. For example, you can loop over them using for … in.
To turn a class into an iterator, you have to implement the __iter__ and __next__ dunder methods.
To stop iteration you raise StopIteration.
To create an iterator:
- Implement __iter__. This will get called once every time before you begin to iterate. It must return a reference to self.
- Implement __next__. This needs to return the objects you will retrieve via iteration.
- Raise StopIteration when you want to stop iterating.
Iterator Example
class NumberGenerator:
def __iter__(self):
self._current = 0
return self
def __next__(self):
self._current += 1
if self._current > 5:
raise StopIteration
return self._current
numbers = NumberGenerator()
for x in numbers:
print(x)1
2
3
4
5
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