Dice probability problem

[Tomi Lindberg]

First, thanks to Antoon and Alexander for replying.

Antoon Pardon wrote:

> It would be better to construct distributions for one
> die and make a function that can 'add' two distributions
> together.

As both replies pointed to this direction, I tried to take 
that route. Here's the unpolished code I came up with. Does 
it look even remotely sane way to accomplish my goal?

-- code begins --

# A die with n faces
D = lambda n: [x+1 for x in range(n)]

# A new die with 6 faces
d6 = D(6)

# Adds another die to results.
def add_dice(sums, die):
     # If first die, all values appear once
     if not sums:
         for face in die:
             sums[face] = 1
     # Calculating the number of appearances for additional
     # dice
     else:
         new_sums = {}
         for k in sums.keys():
             for f in die:
                 if new_sums.has_key(k+f):
                     new_sums[k+f] += sums[k]
                 else:
                     new_sums[k+f] = sums[k]
         sums = new_sums
     return sums

sums = add_dice({}, d6)
sums = add_dice(sums, d6)
sums = add_dice(sums, d6)

-- code ends --

Thanks,
Tomi Lindberg