How to check for single character change in a string?

[Roy Smith]

In article <roy-AAAEEA.10571424122011 at news.panix.com>,
 Roy Smith <roy at panix.com> wrote:

> >>> len([x for x in zip(s1, s2) if x[0] != x[1]])

Heh, Ian Kelly's version:

> sum(a == b for a, b in zip(str1, str2))

is cleaner than mine.  Except that Ian's counts matches and the OP asked 
for non-matches, but that's an exercise for the reader :-)