Dice probability problem

[Alexander Schmolck]

Tomi Lindberg <tomi.lindberg.NO_SPAM at pp.inet.fi.invalid> writes:

> # Adds another die to results.
> def add_dice(sums, die):
>      # If first die, all values appear once

I'd add something like

       sums = sums or {}

because otherwise your function will sometimes mutate sums and sometimes
return a fresh object, which usually is a very bad thing as it can easily lead
to quite nasty bugs.

>      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

'as