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)

Add '%(default)s' to the help parameter to control what is displayed.

parser.add_argument("--type", default="toto", choices=["toto","titi"],
                              help = "type (default: %(default)s)")

Notes:

• It is %+ default in parenthesis + format characters (not to be confused with curly brackets {default} we find in format or f-string)
• Don't forget to add the "specifier character" for the type representation at the end (i.e. s for strings, d for integers, f for floats, etc.)
• You can also add the usual "printf" format specifiers (like number of digits for floats, leading zeros, etc.)

You can refer to printf documentation for more details.