A simple lisp parser

lisp_parser.py

import csv


input = ""
with open('example.lsp', 'r') as input_file:
    for line in input_file:
        if line[0] is not ";":
            input += line

def parse(input):

    this_level = []
    current_token = ""
    index = 0

    while index < len(input):

        if input[index] == "(":

            processed_chars, result = parse(input[index+1:])
            this_level.append(result)
            index += processed_chars

        elif input[index] == ")":

            if current_token is not "":
                this_level.append(current_token)
            return index+1, this_level

        elif input[index] == " ":

            if current_token is not "":
                this_level.append(current_token)
            current_token = ""

        else:

            current_token += input[index]

        index += 1

    return this_level


result = parse(input)
print(result)