Replace one element of a tuple

[Captain Dondo]

I have an array(?) (sorry, I'm new* to python so I'm probably mangling 
the terminology) that looks like this:

[((1028L, datetime.datetime(2006, 5, 30, 7, 0), datetime.datetime(2006, 
5, 30, 7, 30), 'Arthur', 'Prunella Sees the Light; Return of the 
Snowball', 'Prunella prepares for a sleepover with Marina; D.W. protects 
a snowball.', 'Children', 'tooth.seiner.lan', None, 0L, None, 1L, 1L, 
'Default', 9L, 'SH044107', 'EP0441070123', datetime.datetime(2006, 5, 
30, 7, 31, 24), 1164179392L, 0.0, 1, datetime.date(2002, 11, 28), 0, 0L, 
0),), ((1028L, datetime.datetime(2006, 5, 4, 10, 0), 
datetime.datetime(2006, 5, 4, 10, 30), 'Bob the Builder', 'Using Clues', 
'', 'Children', 'tooth.seiner.lan', None, 0L, None, 1L, 1L, 'Default', 
6L, 'SH326087', 'EP3260870141', datetime.datetime(2006, 5, 4, 10, 31, 
30), 1163673536L, 0.0, 1, datetime.date(2005, 3, 19), 0, 0L, 0),)]

I want to replace every instance of 'tooth.seiner.lan' with 'localhost'. 
  There may be lots and lots of these entries (they're pulled from my 
mythtv database).

I could brute-force this by rewriting the whole thing and replacing 
every 9th element but there has to be a better way....

I've looked at various search-and-replace snippets but none that address 
what I am trying to do....

--Yan

*I'm not really new to python, just very very rusty.  Last time I used 
it was about 3 years ago, and I was equally clueless....