Creating a List Lexer/Parser

Question

I need to create a lexer/parser which deals with input data of variable length and structure.

Say I have a list of reserved keywords:

keyWordList = ['command1', 'command2', 'command3']

and a user input string:

userInput = 'The quick brown command1 fox jumped over command2 the lazy dog command 3'
userInputList = userInput.split()

How would I go about writing this function:

INPUT:

tokenize(userInputList, keyWordList)

OUTPUT:
[['The', 'quick', 'brown'], 'command1', ['fox', 'jumped', 'over'], 'command 2', ['the', 'lazy', 'dog'], 'command3']

I've written a tokenizer that can identify keywords, but have been unable to figure out an efficent way to embed groups of non-keywords into lists that are a level deeper.

RE solutions are welcome, but I would really like to see the underlying algorithm as I am probably going to extend the application to lists of other objects and not just strings.

Answer 1

Something like this:

def tokenize(lst, keywords):
    cur = []
    for x in lst:
        if x in keywords:
            yield cur
            yield x
            cur = []
        else:
            cur.append(x)

This returns a generator, so wrap your call in one to list.