formatter_class=argparse.ArgumentDefaultsHelpFormatter

The `formatter_class=argparse.ArgumentDefaultsHelpFormatter` is an argument formatter that can be used with the `ArgumentParser` class in Python's `argparse` module.

When this formatter class is used, the help message generated by the `ArgumentParser` object will include default values for each argument, along with any help text that was provided. This can be useful for helping users understand what the default behavior of the program is and how to modify it if necessary.

For example, if you have an argument defined like this:

parser.add_argument('--threshold', default=0.5, type=float, help='threshold value for filtering')

By default, the help message generated by `ArgumentParser` would look something like this:

usage: my_program.py [-h] [--threshold THRESHOLD]

optional arguments:
  -h, --help            show this help message and exit
  --threshold THRESHOLD
                        threshold value for filtering

However, if you use the `ArgumentDefaultsHelpFormatter`, the help message would look like this:

usage: my_program.py [-h] [--threshold THRESHOLD]

optional arguments:
  -h, --help            show this help message and exit
  --threshold THRESHOLD
                        threshold value for filtering (default: 0.5)

Note the `(default: 0.5)` added to the end of the help text for the `--threshold` argument. This helps users understand that the default threshold value is 0.5, which they can change if necessary.