Comment by qsort

The big missing item from the list: generators!

Using "yield" instead of "return" turns the function into a coroutine. This is useful in all sorts of cases and works very well with the itertools module of the standard library.

One of my favorite examples: a very concise snippet of code that generates all primes:

  def primes():
      ps = defaultdict(list)
      for i in count(2):
          if i not in ps:
              yield i
              ps[i**2].append(i)
          else:
              for n in ps[i]:
                  ps[i + (n if n == 2 else 2*n)].append(n)
              del ps[i]