Often there is a situation when default input arguments need to be converted to a specific type or have a default value of a different type. It's simple to do but can look messy, so I started using this little function.

gistfile1.py

def convert_argument(arg, new_type, default=None):
    """
    Convert an argument to a new type unless it is `None`.
    """
    return default if arg is None else new_type(arg)