def get_input(prompt, default=None, choices=None, option_value=None):
    """
    If option_value is not None, then return it. Otherwise get the result from 
    input.
    """
    if option_value is not None:
        return option_value
    choices = choices or []
    while 1:
        r = input(prompt + ' ').strip()
        if not r and default is not None:
            return default
        if choices:
            if r not in choices:
                r = None
            else:
                break
        else:
            break
    return r
