pets = [["Shoji", "cat", 18], ["Hanako", "dog", 15], ["Sir Toby", "cat", 10],\
        ["Sachiko", "cat", 7], ["Sasha", "dog", 3], ["Lopez", "dog", 13]]

print(pets[3])
print(pets[3][2])

for i in range(len(pets)):
    print(pets[i])
    
# Nested Lists #1
for p in pets:
    print(p)
    
for i in range(len(pets)):
    print(pets[i][1])
    
# Nested Lists #2
for p in pets:
    print(p[1])
    
# Nested Lists #3
dogs = 0
for p in pets:
    if p[1] == 'dog':
        dogs += 1
print(dogs)

# Nested Lists #4
sum_ages = 0
for p in pets:
    sum_ages += p[2]
print(sum_ages)

# Nested Lists #5
def nested_lengths(L):
    lens = []
    for l in L:
        lens.append(len(l))
    return lens

print(nested_lengths(pets))