Python - reemplazar elementos de una matriz

import sys

b =  [[22,56,33] , [21,58,33], [20,51,39]]

b[0][1]=127

a = []

for i in xrange(3):

     a.append([])

     for j in xrange(3):

           if(b[i][j]<=50):

                a[i].append(0)

           else:

                a[i].append(1)

print(b)

print(a)

matriz = [[(22,56,33)], [(21,58,33)], [(20,51,39)]]

def replace_numbers(numbers):

    return [tuple(0 if i <= 50 else 1 for i in numbers[0])]

print(list(map(replace_numbers, matriz)))

b =  [[22,56,33] , [21,58,33], [20,51,39]]

for i in range(0, 3):

    for j in range(0, 3):

        valor = b[i][j]

        if valor <= 50:

            b[i][j] = 0

        else:

            b[i][j] = 1

print b