Argparse: Way to include default values in ‘–help’?

Use the argparse.ArgumentDefaultsHelpFormatter formatter:

parser = argparse.ArgumentParser(
    # ... other options ...
    formatter_class=argparse.ArgumentDefaultsHelpFormatter)

To quote the documentation:

The other formatter class available, ArgumentDefaultsHelpFormatter, will add information about the default value of each of the arguments.

Note that this only applies to arguments that have help text defined; with no help value for an argument, there is no help message to add information about the default value to.

The exact output for your scan-time option then becomes:

  --scan-time [SCAN_TIME]
                        Wait SCAN-TIME seconds between status checks.
                        (default: 5)