Question

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Difference between Python Generators vs Iterators

Generators seem like big deal in Python, new features are added to them now and then and so on.

As far as I can see, instead generators you could always use an object with iterator interface. Is (usually) better conciseness the only benefit of generators or am I missing something?

Answer 1

Yes, iterators are a more general construct, and anything you could do with a generator could be done with an iterator.

However, generators are really nice tool to express certain ideas in a very clean and concise fashion, for which iterators would become cumbersome.

For example, here’s a simple function:

def count_to(m):
    n = 0
    while n <= m:
        yield n
        n += 1

Nice and easy. Here’s the same thing as an iterator:

class CountTo:
    def __init__(self, m):
        self.m = m
        self.n = 0
    def __iter__(self):
        return self
    def next(self):
        if self.n <= self.m:
            cur, self.n = self.n, self.n + 1
            return cur
        else:
            raise StopIteration()

One is 5 lines, the other is 12. The generator expresses the iteration process very succintly, while the iterator obfuscates it with explictly-maintained state and boilerplate code.

A lot of Python’s philosophy is based around readability and simplicity. In keeping with this, I feel that generators offer a nicer interface for a broad class of tasks that would otherwise require iterators. Yes, iterators are more powerful, but the syntactic advantages of generators certainly can’t be overlooked.