def build_person(first_name, last_name, middle_name='', age=None):
    if middle_name and age:
        person = {'first' : first_name, 'middle' : middle_name, 'last' : last_name, 'age': age}
    elif middle_name:
        person = {'first' : first_name, 'middle' : middle_name, 'last' : last_name}
    elif age:
        person = {'first' : first_name, 'last' : last_name, 'age': age}
    else:
        person = {'first' : first_name, 'last' : last_name}
    return person

musician = build_person('John', 'Hooker') #musician -> dict
print(musician)

musician = build_person('John', 'Hooker', 'Lee')
print(musician)

musician = build_person(first_name='John', last_name='Hooker', age=40)
print(musician)

musician = build_person('John', 'Hooker', 'Lee', 40)
print(musician)