看不到输出

Question

items = [("A",5,6),("A",4,5),("A",3,8),("B",6,9),("B",7,4),("C",9,2)]
q2= filter(lambda x: x.count("A"),items)
q4= map(lambda x: x[1], items)
list(q4)
print("Q2 = {}".format(q2))
print("Q4 = {}".format(q4))

I cannot understand why the out put dos not show ?! I try to count how many A in the list and print the 2nd items Q2 = Q4 =

Answer 1

You are filtering the items correctly but then you should apply your next step on q2 because filter does not change items . It returns the result and you are assigning it to q4 . So:

items = [("A",5,6),("A",4,5),("A",3,8),("B",6,9),("B",7,4),("C",9,2)]
q2= filter(lambda x: x.count("A"),items)
q4= map(lambda x: x[1], q2)
list(q4)
print("Q2 = {}".format(q2))
print("Q4 = {}".format(q4))

Answer 2

For your first question:

print map(lambda x: x[0],items).count('A')

Or,

print [i[0] for i in items if i[0]=='A']

For your second question:

print map(lambda x:x[1],items)