Here's a little app to get you started...
import difflib as dl
a = file('file').read()
b = file('file1').read()
sim = dl.get_close_matches
s = 0
wa = a.split()
wb = b.split()
for i in wa:
if sim(i, wb):
s += 1
n = float(s) / float(len(wa))
print '%d%% similarity' % int(n * 100)