What is the difference between an Iterator and a Generator?

Question

What is the difference between an Iterator and a Generator?

Answer 1

Generators are iterators, but not all iterators are generators.

An iterator is typically something that has a next method to get the next element from a stream. A generator is an iterator that is tied to a function.

For example a generator in python:

def genCountingNumbers():
  n = 0
  while True:
    yield n
    n = n + 1

This has the advantage that you don't need to store infinite numbers in memory to iterate over them.

You'd use this as you would any iterator:

for i in genCountingNumbers():
  print i
  if i > 20: break  # Avoid infinite loop

You could also iterate over an array:

for i in ['a', 'b', 'c']:
  print i