pendantic docstring note
Catch error if dictionary does not exist
Also add option to enter path to alternative dictionary.
Fixed error message, added sys.exit()
typo
Bug?
I don't think this is working the way you think it is. To wit:
>>> letters = 'abdefghijklmnopqrstuvwxyz'
>>> for i in range(10):
...     print letters[:i]+letters[i+1:]
...
bcdefghijklmnopqrstuvwxyz
acdefghijklmnopqrstuvwxyz
abdefghijklmnopqrstuvwxyz
abcefghijklmnopqrstuvwxyz
abcdfghijklmnopqrstuvwxyz
abcdeghijklmnopqrstuvwxyz
abcdefhijklmnopqrstuvwxyz
abcdefgijklmnopqrstuvwxyz
abcdefghjklmnopqrstuvwxyz
abcdefghiklmnopqrstuvwxyz
>>> letters[:0]
''
>>> letters[:1]
'a'
>>> letters[0+1:]
'bcdefghijklmnopqrstuvwxyz'

Your program seems to be accidentally exploiting the fact that the i=0 case behaves differently than all the other cases.  It may be doing about n**2 too much work.