[Tutor] Python3 Tutorial question about a[:] = []

[Richard D. Moores]

from <http://docs.python.org/py3k/tutorial/introduction.html#lists> :

>>> # Clear the list: replace all items with an empty list
>>> a[:] = []
>>> a
[]

I've been using
>>> a = []
>>> a
[]

What's the difference?

Thanks,

Dick Moores