Question

What would be the nice way to return something from an iterator one last time when it’s exhausted. I’m using a flag, but this is rather ugly:

class Example():

    def __iter__(self):
        self.lst = [1,2,3]
        self.stop = False # <-- ugly            
        return self

    def next(self):
        if self.stop:  # <-- ugly
            raise StopIteration
        if len(self.lst) == 0:
            self.stop = True            
            return "one last time"
        return self.lst.pop()

Background: I’m fetching an unknown amount of strings from an external source and send them further down to the caller. When the process is over, I want to emit a string “x records processed”. I have no control over calling code, so this must be done inside my iterator.

Answer 1

You could just yield from __iter__ which would turn it into a generator function (alternately you could just write a generator function as suggested by Dan). Just as a warning, this might be misleading to people that abuse the next method.

class Example():

    def __iter__(self):
        lst = [1,2,3]
        for i in reversed(lst):
            yield i
        yield "one last time"