def _between_symbols(string, c1, c2):
    """Grab characters between symbols in a string.
    Will return empty string if nothing is between c1 and c2."""
    for char in [c1, c2]:
        if char not in string:
            raise ValueError("Couldn't find character {} in string {}".format(
                char, string))
    return string[string.index(c1)+1:string.index(c2)]