def build_dict(r):
    '''Return a dictionary where the keys are words in reader r
    and the value for a key is the list of words that were found
    to follow the key.'''
    
    # word_dict: word -> list of words that follow word
    last_word = ""
    word_dict = {}
    for line in r:
        words = line.split()
        for w in words:
            if last_word in word_dict:
                word_dict[last_word].append(w)
            else:
                word_dict[last_word] = [w]
            last_word = w
    # Take care of the special case of the very last word
    # only appearing once - at the end of the file
    if not last_word in word_dict:
        word_dict[last_word] = [""]            
    return word_dict 
               
if __name__ == "__main__":

    filename = "simple.txt"
    infile = open(filename)
    table = build_dict(infile)
    infile.close()
    infile = open(filename)      
    for line in infile:
        print line
    print ""    
    print table