Printing full traceback for exceptions

[scottstanie]

Right now the CLI catches all exceptions and prints only the one top message without context:

MintPy/src/mintpy/__main__.py

Lines 627 to 631 in c305e13

	log.critical(
	"unexpected exception caught: {!r} {}".format(
	type(exc).__name__, exc)
	)
	log.debug("stacktrace:", exc_info=True)

This means that for someone new (like me), I can't really figure out the error without a bunch of searching through the code for the matching phrase instead of having the full line number printed out in the traceback.

Although the stacktrace is printed with log.debug("stacktrace:", exc_info=True), but it's unclear how to enable debug logging, as there's no --debug option.

[yunjunz]

Good point @scottstanie. It's essential to show the full traceback msg, one of Python's best parts. Is there a solution for it? Tagging @avalentino for ideas.

I mainly use individual scripts, such as view.py, and have not used the sub-command style mintpy view much.

[avalentino]

Hi @yunjunz and @scottstanie.
As @scottstanie said the obvious solution is to add a "--debug" option to the CLI arguments,

    parser.add_argument(
        "-d",
        "--debug",
        dest="loglevel",
        action="store_const",
        const="DEBUG",
        help="print debug messages",
    )

and then set the logging level accordingly:

logging.getLogger().setLevel(args.loglevel)

In case you need the full control over the logging level you could add something like the following:

def _add_logging_control_args(parser, default_loglevel=DEFAULT_LOGLEVEL):
    """Add command line options for logging control."""
    loglevels = [logging.getLevelName(level) for level in range(10, 60, 10)]

    parser.add_argument(
        "--loglevel",
        default=default_loglevel,
        choices=loglevels,
        help="logging level (default: %(default)s)",
    )
    parser.add_argument(
        "-q",
        "--quiet",
        dest="loglevel",
        action="store_const",
        const="ERROR",
        help="suppress standard output messages, "
        "only errors are printed to screen",
    )
    parser.add_argument(
        "-v",
        "--verbose",
        dest="loglevel",
        action="store_const",
        const="INFO",
        help="print verbose output messages",
    )
    parser.add_argument(
        "-d",
        "--debug",
        dest="loglevel",
        action="store_const",
        const="DEBUG",
        help="print debug messages",
    )

I typically try to organize my CLI programs according to the template that you can find in the following gist:
https://gist.github.com/avalentino/da77a67147403c8c25260ec7fd72d879

Another option, of course, is to change the log level for the traceback:

log.exception("stacktrace:", exc_info=True)

... but in this case the traceback would be always logged in case of exception.

[yunjunz]

I like your way of full control on the logging level, and the traceback to be always logged in as well in case of exception, will follow a PR for it. Thank you @avalentino!

Update: here is the PR (#1020).