constructors for lists and tuples

[janko hauser]

one can not define empty list/tuples with a predefined length.
it is possible to create a sequence of a given length by multiplying a 
one element sequence.

>>> a=(1,)*3
>>> a
(1, 1, 1)

This is slighly more economic than appending or inserting to an empty
list.

>>> a=[]
>>> a.append(1)
>>> a
[1]

HTH,
__Janko