parser.py

class ParserError(Exception):
    pass
class Sentence(object):
    
    def __init__(self, subject, verb, obj):
        self.subject = subject[1]
        self.verb = verb[1]
        self.object = obj[1]

def peek(word_list):
    if word_list:
        word = word_list[0]
        return word [0]
    else:
        return None
        
def match (word_list, expection):
    if word_list:
        word = word_list.pop(0)
        
        if word[0] ==expection:
            return word
        else:
            return None
        else:
            return None

def skip(word_list, word_type):
    while peek(word_list) == word_type:
        match(word_list, word_type)

def parse_verb(word_list):
    skip(word_list, 'stop'):
        
    if peek(word_list) =='verb':
        return match(word_list, 'verb')
    else:
        raise ParserError("Expection a verb next.")

def parse_object(word_list):
    skip(word_list, 'stop')
    next_word = peek(word_list)
    
    if next_word == 'noun':
        return match(word_list, 'noun')
    elif next_word == 'direction':
        return match(word_list, 'direction')
    else:
        raise ParserError("Expected a noun or direction next.")

def parse_sentence(word_list):
    subj = parse_subject(word_list)
    verb = parse_verb(word_list)
    obj = parse_object(word_list)
    
    return Sentence(subj, verb, obj)

//nice job