lisp parser

lisp.py

def token_to_atom(token):
    ''' ints, floats converted, everything else string '''
    if token[0] in '1234567890':
        if '.' in token:
            return float(token)
        return int(token)
    return token

def tokens_to_tree(tokens):
    ''' take out parens, nest lists '''
    res = []
    while tokens:
        t = tokens.pop(0)
        if t == ')':
            return res
        elif t == '(':
            res.append(tokens_to_tree(tokens))
        else:
            res.append(token_to_atom(t))
    return res[0]

def parse(code):
    tokens = (code.
        replace('(', ' ( ').
        replace(')', ' ) ').
        split())
    return tokens_to_tree(tokens)

code = '(first (list 1 (+ 2 3) 9))'
result = ['first', ['list', 1, ['+', 2, 3], 9]]
assert parse(code) == result