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```#!/usr/bin/env python3

def square_list(a, b, value=0) :
return [[value,] * b for j in range(a)]

def arg_min(* arg_list) :
arg_s = None
for i, arg in enumerate(arg_list) :
if i == 0 or arg < arg_s :
arg_s = arg
i_s = i
return i_s, arg_s

MODIFIED = 0
DELETED = 1
CREATED = 2

def levenshtein_distance(a, b) :
""" return the levenshtein distance between two strings of list of """

len_a = len(a)
len_b = len(b)

d = square_list(len_a+1, len_b+1)

for i in range(1, len_a+1) :
d[i][0] = i
for j in range(1, len_b+1) :
d[0][j] = j

for j in range(1, len_b+1) :
for i in range(1, len_a+1) :
if a[i-1] == b[j-1] :
d[i][j] = d[i-1][j-1]
else :
d[i][j] = min(d[i-1][j], d[i][j-1], d[i-1][j-1]) + 1
return d[-1][-1]

def levenshtein_sequence(a, b) :
""" return an explicit list of difference between a and b """

len_a = len(a)
len_b = len(b)

s = list()

d = square_list(len_a+1, len_b+1)

for i in range(1, len_a+1) :
d[i][0] = i
for j in range(1, len_b+1) :
d[0][j] = j

for j in range(1, len_b+1) :
for i in range(1, len_a+1) :
if a[i-1] == b[j-1] :
d[i][j] = d[i-1][j-1]
else :
d[i][j] = min(d[i-1][j], d[i][j-1], d[i-1][j-1]) + 1

prev_i, prev_j = i, j
while i > 0 and j > 0 :
if i == 1 and j == 1 :
if prev_i != i and prev_j != j :
u = MODIFIED
elif prev_i == i :
u = CREATED
elif prev_j == j :
u = DELETED
new_i, new_j = i-1, j-1
elif i == 1 :
new_i, new_j = i, j-1
u = CREATED
elif j == 1 :
u = DELETED
new_i, new_j = i-1, j
else :
u, null = arg_min(d[i-1][j-1], d[i-1][j], d[i][j-1])
new_i, new_j = i - (1,1,0)[u], j - (1,0,1)[u]
op = '*-+'[u] if d[i][j] != d[new_i][new_j] else '='
s.append((op, i-1, j-1))
prev_i, prev_j = i, j
i, j = new_i, new_j

return list(reversed(s))
```

#### Diff to Previous Revision

```--- revision 2 2014-01-15 07:52:33
+++ revision 3 2014-01-15 09:14:30
@@ -56,7 +56,7 @@
if a[i-1] == b[j-1] :
d[i][j] = d[i-1][j-1]
else :
-				d[i][j] = min(d[i-1][j], d[i][j-1],	d[i-1][j-1]) + 1
+				d[i][j] = min(d[i-1][j], d[i][j-1], d[i-1][j-1]) + 1

prev_i, prev_j = i, j
while i > 0 and j > 0 :
```