Creating Lexicon and Scanner in Python

Question

I'm new here in the world of coding and I haven't received a very warm welcome. I've been trying to learn python via the online tutorial http://learnpythonthehardway.org/book/. I've been able to struggle my way through the book up until exercise 48 & 49. That's where he turns students loose and says "You figure it out." But I simply can't. I understand that I need to create a Lexicon of possible words and that I need to scan the user input to see if it matches anything in the Lexicon but that's about it! From what I can tell, I need to create a list called lexicon:

lexicon = [
    ('directions', 'north'),
    ('directions', 'south'),
    ('directions', 'east'),
    ('directions', 'west'),
    ('verbs', 'go'),
    ('verbs', 'stop'),
    ('verbs', 'look'),
    ('verbs', 'give'),
    ('stops', 'the'),
    ('stops', 'in'),
    ('stops', 'of'),
    ('stops', 'from'),
    ('stops', 'at')
]

Is that right? I don't know what to do next? I know that each item in the list is called a tuple, but that doesn't really mean anything to me. How do I take raw input and assign it to the tuple? You know what I mean? So in exercise 49 he imports the lexicon and just inside python prints lexicon.scan("input") and it returns the list of tuples so for example:

from ex48 import lexicon
>>> print lexicon.scan("go north")
[('verb', 'go'), ('direction', 'north')]

Is 'scan()' a predefined function or did he create the function within the lexicon module? I know that if you use 'split()' it creates a list with all of the words from the input but then how does it assign 'go' to the tuple ('verb', 'go')?

Am I just way off? I know I'm asking a lot but I searched around everywhere for hours and I can't figure this one out on my own. Please help! I will love you forever!

Answer 1

I wouldn't use a list to make the lexicon. You're mapping words to their types, so make a dictionary.

Here's the biggest hint that I can give without writing the entire thing:

lexicon = {
    'north': 'directions',
    'south': 'directions',
    'east': 'directions',
    'west': 'directions',
    'go': 'verbs',
    'stop': 'verbs',
    'look': 'verbs',
    'give': 'verbs',
    'the': 'stops',
    'in': 'stops',
    'of': 'stops',
    'from': 'stops',
    'at': 'stops'
}

def scan(sentence):
    words = sentence.lower().split()
    pairs = []

    # Iterate over `words`,
    # pull each word and its corresponding type
    # out of the `lexicon` dictionary and append the tuple
    # to the `pairs` list

    return pairs

Answer 2

Based on the ex48 instructions, you could create a few lists for each kind of word. Here's a sample for the first test case. The returned value is a list of tuples, so you can append to that list for each word given.

direction = ['north', 'south', 'east', 'west', 'down', 'up', 'left', 'right', 'back']

class Lexicon:
    def scan(self, sentence):
        self.sentence = sentence
        self.words = sentence.split()
        stuff = []
        for word in self.words:
            if word in direction:
                stuff.append(('direction', word))
        return stuff

lexicon = Lexicon()

He notes that numbers and exceptions are handled differently.

Answer 3

Finally I did it!

lexicon = {
    ('directions', 'north'),
    ('directions', 'south'),
    ('directions', 'east'),
    ('directions', 'west'),
    ('verbs', 'go'),
    ('verbs', 'stop'),
    ('verbs', 'look'),
    ('verbs', 'give'),
    ('stops', 'the'),
    ('stops', 'in'),
    ('stops', 'of'),
    ('stops', 'from'),
    ('stops', 'at')
    }

def scan(sentence):

    words = sentence.lower().split()
    pairs = []

    for word in words:
        word_type = lexicon[word]
        tupes = (word, word_type) 
        pairs.append(tupes)

    return pairs