when_offered_course.py

# let's assume you are planning on taking some additional courses at your local educational institution, and you have acquired some data about the available courses and when they will be offered. In the following exercise, you will write control structures to process the data and return the semesters when a given course is offered.
# You will need to complete the function when_offered(courses, course). This function accepts a "courses" data structure and a "course" string. The function should return a list of strings representing the semesters when the input course is offered. See the two test cases below for examples of correct results.


courses = {
    'spring2020': { 'cs101': {'name': 'Building a Search Engine',
                           'teacher': 'Dave',
                           'assistant': 'Peter C.'},
                 'cs373': {'name': 'Programming a Robotic Car',
                           'teacher': 'Sebastian',
                           'assistant': 'Andy'}},
    'fall2020': { 'cs101': {'name': 'Building a Search Engine',
                           'teacher': 'Dave',
                           'assistant': 'Sarah'},
                 'cs212': {'name': 'The Design of Computer Programs',
                           'teacher': 'Peter N.',
                           'assistant': 'Andy',
                           'prereq': 'cs101'},
                 'cs253': {'name': 'Web Application Engineering - Building a Blog',
                           'teacher': 'Steve',
                           'prereq': 'cs101'},
                 'cs262': {'name': 'Programming Languages - Building a Web Browser',
                           'teacher': 'Wes',
                           'assistant': 'Peter C.',
                           'prereq': 'cs101'},
                 'cs373': {'name': 'Programming a Robotic Car',
                           'teacher': 'Sebastian'},
                 'cs387': {'name': 'Applied Cryptography',
                           'teacher': 'Dave'}},
    'spring2044': { 'cs001': {'name': 'Building a Quantum Holodeck',
                           'teacher': 'Dorina'},
                        'cs003': {'name': 'Programming a Robotic Robotics Teacher',
                           'teacher': 'Jasper'},
                     }
    }


def when_offered(courses, course):
    semesters = []
    for key in courses:
        semester = courses[key]
        if course in semester.keys():
            semesters.append(key)
    return semesters



print(when_offered(courses, 'cs101'))
# Correct result: 
# ['fall2020', 'spring2020']

print(when_offered(courses, 'bio893'))
# Correct result: 
# []