python - TypeError: string indices must be integers, not str // working with dict

Question

I am trying to define a procedure, involved(courses, person), that takes as input a courses structure and a person and returns a Dictionary that describes all the courses the person is involved in.

Here is my involved(courses, person) function:

def involved(courses, person):
    for time1 in courses:
        for course in courses[time1]:
            for info in time1[course]:
                print info

Here is my dictionary:

courses = {
    'feb2012': { 'cs101': {'name': 'Building a Search Engine',
                           'teacher': 'Dave',
                           'assistant': 'Peter C.'},
                 'cs373': {'name': 'Programming a Robotic Car',
                           'teacher': 'Sebastian',
                           'assistant': 'Andy'}},
    'apr2012': { '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'}},
    'jan2044': { 'cs001': {'name': 'Building a Quantum Holodeck',
                           'teacher': 'Dorina'},
               'cs003': {'name': 'Programming a Robotic Robotics Teacher',
                           'teacher': 'Jasper'},
                     }
    }

When I'm trying to test my code:

>>>print involved(courses, 'Dave')

Python give me an error:

for info in time1[course]:
TypeError: string indices must be integers, not str

How can I fix that?

Thanks.

Answer 1

time1 is the key of the most outer dictionary, eg, feb2012. So then you're trying to index the string, but you can only do this with integers. I think what you wanted was:

for info in courses[time1][course]:

As you're going through each dictionary, you must add another nest.