Here is a profile run of the 200 line case, run on the 3.x trunk, and  with all the trivial functions removed.  quick_ratio and __contains__ dominate the time.  The process was CPU bound, memory usage stayed low.


17083154 function calls (17066360 primitive calls) in 248.779 CPU seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
 10660375   70.516    0.000   70.516    0.000 :0(__contains__)
   114482    1.048    0.000    1.048    0.000 :0(append)
  4434776   29.254    0.000   29.254    0.000 :0(get)
685047/685042    4.400    0.000    4.400    0.000 :0(len)
   197349    1.512    0.000    1.512    0.000 :0(min)
   197133    1.452    0.000    1.452    0.000 difflib.py:228(set_seq1)
     2500    1.632    0.001    3.092    0.001 difflib.py:299(__chain_b)
     1082    2.520    0.002    4.768    0.004 difflib.py:350(find_longest_match)
   339143    2.580    0.000    2.580    0.000 difflib.py:40(_calculate_ratio)
   141727  120.599    0.001  220.970    0.002 difflib.py:661(quick_ratio)
   196736    6.956    0.000   12.549    0.000 difflib.py:690(real_quick_ratio)
 8974/794    5.052    0.001  248.431    0.313 difflib.py:945(_fancy_replace)