all Python 3argparseterm

argparse.ArgumentParser

parser

A command-line argument parser: you declare arguments with add_argument(), and parse_args() turns a list of strings into a Namespace of ready values.

Syntax

parser = argparse.ArgumentParser(prog=None, description=None, formatter_class=..., allow_abbrev=True, exit_on_error=True)

On bad input parse_args() does not raise an ordinary exception: it prints the usage to stderr and calls sys.exit(2), i.e. SystemExit, which except Exception does not catch. To get an ArgumentError instead, pass exit_on_error=False. Long options are matched by prefix by default, so '--verb' works as '--verbose' unless allow_abbrev=False. Called with no argument, parse_args() reads sys.argv[1:], so pass a list explicitly in tests.

Examples

import argparse
parser = argparse.ArgumentParser(prog='app')
parser.add_argument('--n', type=int, default=1)
parser.add_argument('--verbose', action='store_true')
print(parser.parse_args(['--n', '3']))  # → Namespace(n=3, verbose=False)
print(parser.parse_args(['--verb']))  # → Namespace(n=1, verbose=True) — префикс опции

# Python 3.9+
import argparse
parser = argparse.ArgumentParser(prog='app', exit_on_error=False)
parser.add_argument('--n', type=int)
try:
    parser.parse_args(['--n', 'x'])
except argparse.ArgumentError as e:
    print(e)  # → argument --n: invalid int value: 'x'

import argparse
parser = argparse.ArgumentParser(prog='app')
try:
    parser.parse_args(['--oops'])
except SystemExit as e:
    print('код выхода', e.code)  # → код выхода 2

See also

Common errors

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