How can I format the string according to its length at runtime?

[ed_tsang at yahoo.com]

I am trying to supply the precision formating at run time:

s = 123
print '(0x%-6X -)'%s

where I try to dynamically supply the number 6 from (6- length of s), 
I can't find a way to dynamically supply that. 

Anyone hav any idea?
Thanks