String formatting with fixed width

[Alexander Eisenhuth]

Hello alltogether,

is it possible to format stings with fixed width of let's say 7 character. T 
need a floating point with 3 chars before dot, padded with ' ' and 3 chars after 
dot, padded with '0'.

Followingh is my approach
 >>> f = 21.1
 >>> s = "%.03f" % f
 >>> s
'21.100'

But there are missing ' '. How can I get that? (For bigger numbers than 999 they 
might be cut: 1021 -> 021)

Thanks,
Alexander