[aviv]

Try this for when you need to fill 2 blank tiles:

  import string
  from itertools import product
  
  w = "H_LL_"
  w_fmt = w.replace('_', '%s')
  
  product_args = [list(string.uppercase)] * 2
  
  expanded = [w_fmt % repl for repl in product(*product_args)]

[fragmede]

(requires python2.6 - http://docs.python.org/library/itertools.html#itertools.prod... )

[noaharc]

Many thanks! I'm using it now.