Given a string, return a list of math symbol tokens

def tokenize(string, language=None, escape='___'):
    """
    Given a string, return a list of math symbol tokens
    """
    # Set all words to lowercase
    string = string.lower()

    # Ignore punctuation
    if len(string) and not string[-1].isalnum():
        character = string[-1]
        string = string[:-1] + ' ' + character

    # Parenthesis must have space around them to be tokenized properly
    string = string.replace('(', ' ( ')
    string = string.replace(')', ' ) ')

    if language:
        words = mathwords.words_for_language(language)

        for phrase in words:
            escaped_phrase = phrase.replace(' ', escape)
            string = string.replace(phrase, escaped_phrase)

    tokens = string.split()

    for index, token in enumerate(tokens):
        tokens[index] = token.replace(escape, ' ')

    return tokens