Python Generator

lxw Python_Cookbook$ p
Python 3.4.0 (default, Apr 11 2014, 13:05:18) 
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> def countdown(n):
...     print("Start to count from", n)
...     while n > 0:
...          yield n
...          n -= 1
...     print("Done!")
... 
>>> c = countdown(3)
>>> c
<generator object countdown at 0xb7234c5c>
>>> for item in c:
...     print(item)
... 
Start to count from 3
3
2
1
Done!

>>> d = countdown(3)
>>> d
<generator object countdown at 0xb711a43c>
>>> next(d)
Start to count from 3
3
>>> next(d)
2
>>> next(d)
1
>>> next(d)
Done!
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration
>>>