Difference between Python's Generators and Iterators

Question

What is the difference between iterators and generators? Some examples for when you would use each case would be helpful.

Answer 1

Examples from Ned Batchelder highly recommended for iterators and generators

A method without generators that do something to even numbers

def evens(stream):
   them = []
   for n in stream:
      if n % 2 == 0:
         them.append(n)
   return them

while by using a generator

def evens(stream):
    for n in stream:
        if n % 2 == 0:
            yield n

• We don't need any list nor a return statement
• Efficient for large/ infinite length stream ... it just walks and yield the value

Calling the evens method (generator) is as usual

num = [...]
for n in evens(num):
   do_smth(n)

• Generator also used to Break double loop

Iterator

A book full of pages is an iterable, A bookmark is an iterator

and this bookmark has nothing to do except to move next

litr = iter([1,2,3])
next(litr) ## 1
next(litr) ## 2
next(litr) ## 3
next(litr) ## StopIteration  (Exception) as we got end of the iterator

To use Generator ... we need a function

To use Iterator ... we need next and iter

As been said:

A Generator function returns an iterator object

The Whole benefit of Iterator:

Store one element a time in memory