And somewhat golfed more space-efficient Python 3 versions:

def minimumDeleteSum(self, s, t):
a = [0] * (len(t) + 1)
for c in s:
a, b = [0], a
for d, x, y, z in zip(t, b, b[1:], a):
a += x + ord(c) if c == d else max(y, z),
return sum(map(ord, s + t)) - 2 * a[-1]

and

def minimumDeleteSum(self, s, t):
a = [0] * (len(t) + 1)
for c in s:
a, b = [0], a
for d, x, y in zip(t, b, map(max, b[1:], a)):
a += x + ord(c) if c == d else y,
return sum(map(ord, s + t)) - 2 * a[-1]

and a particularly lazy one:

def minimumDeleteSum(self, s, t):
a = [0] * (len(t) + 1)
for c in s:
a, b = [0], a
a += (x + ord(c) if c == d else y for d, x, y in zip(t, b, map(max, b[1:], a)))
return sum(map(ord, s + t)) - 2 * a[-1]