Используйте код ниже:
dict1 = {'Brazil': [19000000, 810000.00], 'Japan': [128000000, 350000.0]} #initial dict
def addToDict(c, p, a):
#add new values to dict1, here we are adding country(c) as key, [population(p), area(a)] as value.
dict1[c] = [p, a] #dict[c] = [p,a] <-- [p,a] are values assigned to the key identified-in/new-key in dict1
return dict1 #optional - I used it just to see the final value.
print (addToDict('India', 1000000000, 10098978.778)) #main call
#result --> {'Brazil': [19000000, 810000.0], 'Japan': [128000000, 350000.0], 'India': [1000000000, 10098978.778]}