Introduction to Data Science in python by University of Michigan

Mates I am trying to solve the assignment 1 

Question : 

Part B

The dataset file in assets/grades.txt contains a line separated list of people with their grade in a class. Create a regex to generate a list of just those students who received a B in the course.?

My Solution 

import re
def grades():
    with open ("assets/grades.txt", "r") as file:
        grades = file.read()

    # YOUR CODE HERE
    namesB=[ ]
    for item in re.finditer("(?P<name>.*)(\: B)",grades):
        namesB.append(item.group('name'))
        return namesB
    raise NotImplementedError()

grades()

assert len(grades()) == 16

I suppose to get 16 PEOPLE WHO GOT B in their course but it shows only 1 guy in the out put i dont understand wts wrong with my codes… Mates help plz