meet it

turns command-line words into checked values.

Real tools are started from a , like logcheck app.log --top 3. The words after the name are command-line arguments. The argparse module reads them, converts them and checks them, so your code only ever sees clean values.

add_argument("file") makes a positional argument that must be given. A name with two dashes, like --top, makes an , with a type, a default or a list of choices. action="store_true" makes a flag that is True when present.

Gwecode has no command line, so pass the words to parse_args as a list. It works the same way.

import argparse

parser = argparse.ArgumentParser(prog="logcheck")
parser.add_argument("file")
parser.add_argument("--top", type=int, default=5)
parser.add_argument("--level", choices=["INFO", "ERROR"], default="INFO")

args = parser.parse_args(["app.log", "--top", "3"])
print(args.file, args.top, args.level)
print(args.top * 2)

A real program calls parser.parse_args() with no list, and argparse reads whatever was typed.

guess first

The words come in a funny order. What will this show?

Guess before you run it. Wrong guesses are how you learn, and nothing is marked.

import argparse

parser = argparse.ArgumentParser(prog="greet")
parser.add_argument("name")
parser.add_argument("--times", type=int, default=1)
parser.add_argument("--shout", action="store_true")

args = parser.parse_args(["--shout", "Ana", "--times", "2"])
name = args.name
if args.shout:
    name = name.upper()
print(name, args.times, args.shout)

your turn

Your turn. Order some pizzas from the command line.

Name the option --count in the first blank. Then pass a size of small or large, and a number of pizzas, in the list.

Your code

press run to see what happens

fix it

The discount crashes. Fix it!

Broken code to fix

press run to see what happens

The error says text and a number were mixed. What type is args.percent?
Command-line arguments always arrive as text unless you tell argparse to convert them.
Add type=int to the --percent line, then run.

nailed it

your tools take orders from the command line. :D

argparse reads, converts and checks command-line arguments.
Positional arguments are required. Options can have defaults.
Pass a list to parse_args to try out your tool.

new words in your collection

command line
command-line argument
argparse
option

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argparse turns command-line words into checked values.

The words come in a funny order. What will this show?

Your turn. Order some pizzas from the command line.

The discount crashes. Fix it!

your tools take orders from the command line. :D

turns command-line words into checked values.