Python - Combo

from collections import OrderedDict

def sumar_valores(m, n):

    result = {}

    for k, v in m.items():

        if k in n:

            result[k] = v + n[k]

        else:

            result[k] = v

    for k, v in n.items():

        if k not in result:

            result[k] = v

    return result

a = 'carne=10, leche=20, arroz=10, agua=5'.replace(' ', '').split(',')

b = 'carne=4, arroz=5, azucar=10'.replace(' ', '').split(',')

x = {i.split('=')[0]:int(i.split('=')[1]) for i in a}

z = {i.split('=')[0]:int(i.split('=')[1]) for i in b}

result = OrderedDict(sorted(sumar_valores(z, x)items()))

for k, v in result.items():

    print(k, v)