checking timestamp_format for working with dateutil.parser.parse
checking timestamp_format for working with dateutil.parser.parse

It is allowed to change the timestamp format in nbgrader_config.py. But e.g. c.Exchange.timestamp_format = "%Y-%m-%d-%H-%M-%S-%f" will raise a ValueError('Unknown string format:', '2019-10-24-20-25-53-460007') in dateutil.parser.parse during collect of submissions. This is due to the new dependency of dateutil.parser.parse in parse_utc().
To avoid this during collection of submission, the above code will check the timestamp_format against dateutils parsing algorithm and raises an configuration error.
jhamrick/nbgrader,jupyter/nbgrader,jhamrick/nbgrader,jupyter/nbgrader,jhamrick/nbgrader,jupyter/nbgrader,jupyter/nbgrader,jupyter/nbgrader,jhamrick/nbgrader