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.

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.