ud3.py

# Define a procedure, add_to_index,
# that takes 3 inputs:

# - an index: [[<keyword>,[<url>,...]],...]
# - a keyword: String
# - a url: String

# If the keyword is already
# in the index, add the url
# to the list of urls associated
# with that keyword.

# If the keyword is not in the index,
# add an entry to the index: [keyword,[url]]

index = []
def add_to_index(index,keyword,url):
    #i=0
    p=0
    for x in range(len(index)):
        if index==[]:
            index.append([keyword,[url]])
            return index
        else:
            if keyword in index[x]:
                index[x][1].append(url)
                p=1
                return index
    if p==0:
        index.append([keyword,[url]])

add_to_index(index,'udacity','http://udacity.com')
add_to_index(index,'computing','http://acm.org')
add_to_index(index,'udacity','http://npr.org')
print index
                                                                                    #>>> [['udacity', ['http://udacity.com', 'http://npr.org']], 
                                                                                    #>>> ['computing', ['http://acm.org']]]