a trick with lists ?

[Sébastien Vincent]

I've found some class on the Net which takes basically this form :

######
class Foo:
    def __init__(self):
        self.tasks = []
   ...

    def method1(self):
        tasks = []
        while True:
  ...
  append/pop elements into/from tasks
  ...
  if condition : break

    self.tasks[:] = tasks
        return
######

What I do not fully understand is the line "self.tasks[:] = tasks". Why does 
the guy who coded this did not write it as "self.tasks = tasks"? What is the 
use of the "[:]" trick ?