small terrible lisp ast parser

lisp.py

import re

def lex(s):
    return re.findall("(\(|\)|[\w\*\+\-]+)", s)

def get_ast(tokens):
    ast = []
    while tokens:
        t = tokens.pop(0)
        if t == '(':
            while t != ')' and tokens:
                ast.append(get_ast(tokens))
        elif t == ')':
            break
        else:
            if t.isdigit():
                ast.append(float(t))
            else:
                ast.append(t)
    if not ast:
        raise SyntaxError("idk dude")
    return ast

print get_ast(lex("(+ (* 2 4) 3)"))
# => [['+', ['*', 2.0, 4.0], [3.0]]]