This code works properly to increase the width of the help text, but it's unclear. What is the lambda function doing?
EDIT: To clarify, the question is not Why are lambda functions useful in general, but instead, how is the argument parser init code using the lambda function?
import argparse
import sys
formatter = lambda prog: argparse.HelpFormatter(prog, width=100)
dummy_text = """Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut
enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi
ut aliquip ex ea commodo consequat. Duis aute irure dolor in
reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla
pariatur. Excepteur sint occaecat cupidatat non proident, sunt in
culpa qui officia deserunt mollit anim id est laborum."""
parser = argparse.ArgumentParser(description=dummy_text, formatter_class=formatter)
parser.add_argument("-e", dest="destE", help=dummy_text)
parser.add_argument("-w", dest="destW", help=dummy_text)
args = parser.parse_args(sys.argv)