Python Distilled

6. Generators

Generator functions are one of Python’s most interesting and powerful features. Generators are often presented as a convenient way to define new kinds of iteration patterns. However, there is much more to them: Generators can also fundamentally change the whole execution model of functions. This chapter discusses generators, generator delegation, generator-based coroutines, and common applications of generators.

6.1 Generators and yield

If a function uses the yield keyword, it defines an object known as a generator. The primary use of a generator is to produce values for use in iteration. Here’s an example:

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def countdown(n):
     print('Counting down from', n)
     while n > 0:
          yield n
          n -= 1

# Example use ...