def parse_int(int_str):
    """Parse a string of the form 1,234,567b into a Python integer.
       The terminal letter, if present, indicates e.g. billions."""
    int_str = int_str.replace(',', '')

    factor = __get_factor(int_str)
    if factor != 1:
        int_str = int_str[:-1]

    try:
        return int(int_str.replace(',', '')) * factor
    except ValueError:
        return None