[雪峰磁针石博客]python库介绍-argparse: 命令行选项及参数解析

快速入门

argparse是一个完整的参数处理库。参数可以根据add_argument()的action选项触发不同action。支持的action有存储参数（单个，或作为列表的一部分）;存储常量的值（对布尔开关true/false有特殊处理）。默认动作是存储参数值。支持type(指定存储类型)和dest(指定存储变量)等参数。

然后使用函数parse_args()进行参数解析，这个函数的输入默认是sys.argv[1:]，也可以使用其他字符串列表。选项使用GNU/POSIX语法处理，可以混合选项和参数值。parse_args的返回值是一个包含命令参数的Namespace。所有参数以属性的形式存在，比如args.myoption。

下面是一个简单的示例：argparse_short.py

import argparse

parser = argparse.ArgumentParser(description='Short sample app')

parser.add_argument('-a', action="store_true", default=False)
parser.add_argument('-b', action="store", dest="b")
parser.add_argument('-c', action="store", dest="c", type=int)

print(parser.parse_args(['-a', '-bval', '-c', '3']))

执行结果：

$ python3 argparse_short.py
Namespace(a=True, b='val', c=3)

长参数argparse_long.py

import argparse

parser = argparse.ArgumentParser(
    description='Example with long option names',
)

parser.add_argument('--noarg', action="store_true",
                    default=False)
parser.add_argument('--witharg', action="store",
                    dest="witharg")
parser.add_argument('--witharg2', action="store",
                    dest="witharg2", type=int)

print(
    parser.parse_args(
        ['--noarg', '--witharg', 'val', '--witharg2=3']
    )
)

执行结果

$ python3 argparse_long.py

Namespace(noarg=True, witharg='val', witharg2=3)

混合可选和必选参数：argparse_arguments.py

import argparse

parser = argparse.ArgumentParser(
    description='Example with nonoptional arguments',
)

parser.add_argument('count', action="store", type=int)
parser.add_argument('units', action="store")

print(parser.parse_args())

执行结果

$ python3 argparse_arguments.py 3 inches

Namespace(count=3, units='inches')

$ python3 argparse_arguments.py some inches

usage: argparse_arguments.py [-h] count units
argparse_arguments.py: error: argument count: invalid int value:
'some'

$ python3 argparse_arguments.py

usage: argparse_arguments.py [-h] count units
argparse_arguments.py: error: the following arguments are
required: count, units

参数action有：

store：默认action模式，存储值到指定变量。
store_const：存储值在参数的const部分指定，多用于实现非布尔的命令行flag。
store_true / store_false：布尔开关。可以2个参数对应一个变量。
append：存储值到列表，该参数可以重复使用。
append_const：存储值到列表，存储值在参数的const部分指定。
version 输出版本信息然后退出。

下面是各种action的示例：argparse_action.py

import argparse

parser = argparse.ArgumentParser()

parser.add_argument('-s', action='store',
                    dest='simple_value',
                    help='Store a simple value')

parser.add_argument('-c', action='store_const',
                    dest='constant_value',
                    const='value-to-store',
                    help='Store a constant value')

parser.add_argument('-t', action='store_true',
                    default=False,
                    dest='boolean_t',
                    help='Set a switch to true')
parser.add_argument('-f', action='store_false',
                    default=True,
                    dest='boolean_f',
                    help='Set a switch to false')

parser.add_argument('-a', action='append',
                    dest='collection',
                    default=[],
                    help='Add repeated values to a list')

parser.add_argument('-A', action='append_const',
                    dest='const_collection',
                    const='value-1-to-append',
                    default=[],
                    help='Add different values to list')
parser.add_argument('-B', action='append_const',
                    dest='const_collection',
                    const='value-2-to-append',
                    help='Add different values to list')

parser.add_argument('--version', action='version',
                    version='%(prog)s 1.0')

results = parser.parse_args()
print('simple_value     = {!r}'.format(results.simple_value))
print('constant_value   = {!r}'.format(results.constant_value))
print('boolean_t        = {!r}'.format(results.boolean_t))
print('boolean_f        = {!r}'.format(results.boolean_f))
print('collection       = {!r}'.format(results.collection))
print('const_collection = {!r}'.format(results.const_collection))

执行结果如下，注意'simple_value'等被自动化转化为大写

$ python3 argparse_action.py -h

usage: argparse_action.py [-h] [-s SIMPLE_VALUE] [-c] [-t] [-f]
                          [-a COLLECTION] [-A] [-B] [--version]

optional arguments:
  -h, --help       show this help message and exit
  -s SIMPLE_VALUE  Store a simple value
  -c               Store a constant value
  -t               Set a switch to true
  -f               Set a switch to false
  -a COLLECTION    Add repeated values to a list
  -A               Add different values to list
  -B               Add different values to list
  --version        show program's version number and exit

$ python3 argparse_action.py -s value

simple_value     = 'value'
constant_value   = None
boolean_t        = False
boolean_f        = True
collection       = []
const_collection = []

$ python3 argparse_action.py -c

simple_value     = None
constant_value   = 'value-to-store'
boolean_t        = False
boolean_f        = True
collection       = []
const_collection = []

$ python3 argparse_action.py -t

simple_value     = None
constant_value   = None
boolean_t        = True
boolean_f        = True
collection       = []
const_collection = []

$ python3 argparse_action.py -f

simple_value     = None
constant_value   = None
boolean_t        = False
boolean_f        = False
collection       = []
const_collection = []

$ python3 argparse_action.py -a one -a two -a three

simple_value     = None
constant_value   = None
boolean_t        = False
boolean_f        = True
collection       = ['one', 'two', 'three']
const_collection = []

$ python3 argparse_action.py -B -A

simple_value     = None
constant_value   = None
boolean_t        = False
boolean_f        = True
collection       = []
const_collection = ['value-2-to-append', 'value-1-to-append']

$ python3 argparse_action.py --version

argparse_action.py 1.0

可选前缀

ArgumentParser函数中的选项prefix_chars可以指定前缀。默认使用UNIX风格，命令行使用‘-’作为前缀。可以使用windows的’/’或者其他符号。

argparse_prefix_chars.py

import argparse

parser = argparse.ArgumentParser(
    description='Change the option prefix characters',
    prefix_chars='-+/',
)

parser.add_argument('-a', action="store_false",
                    default=None,
                    help='Turn A off',
                    )
parser.add_argument('+a', action="store_true",
                    default=None,
                    help='Turn A on',
                    )
parser.add_argument('//noarg', '++noarg',
                    action="store_true",
                    default=False)

print(parser.parse_args())

执行结果

$ python3 argparse_prefix_chars.py -h

usage: argparse_prefix_chars.py [-h] [-a] [+a] [//noarg]

Change the option prefix characters

optional arguments:
  -h, --help        show this help message and exit
  -a                Turn A off
  +a                Turn A on
  //noarg, ++noarg

$ python3 argparse_prefix_chars.py +a

Namespace(a=True, noarg=False)

$ python3 argparse_prefix_chars.py -a

Namespace(a=False, noarg=False)

$ python3 argparse_prefix_chars.py //noarg

Namespace(a=None, noarg=True)

$ python3 argparse_prefix_chars.py ++noarg

Namespace(a=None, noarg=True)

$ python3 argparse_prefix_chars.py --noarg

usage: argparse_prefix_chars.py [-h] [-a] [+a] [//noarg]
argparse_prefix_chars.py: error: unrecognized arguments: --noarg

处理配置文件中的参数

argparse_with_shlex.py

import argparse
from configparser import ConfigParser
import shlex

parser = argparse.ArgumentParser(description='Short sample app')

parser.add_argument('-a', action="store_true", default=False)
parser.add_argument('-b', action="store", dest="b")
parser.add_argument('-c', action="store", dest="c", type=int)

config = ConfigParser()
config.read('argparse_with_shlex.ini')
config_value = config.get('cli', 'options')
print('Config  :', config_value)

argument_list = shlex.split(config_value)
print('Arg List:', argument_list)

print('Results :', parser.parse_args(argument_list))

其中argparse_with_shlex.ini文件的内容如下：

[cli]
options = -a -b 2

执行结果

$ python3 argparse_with_shlex.py

Config  : -a -b 2
Arg List: ['-a', '-b', '2']
Results : Namespace(a=True, b='2', c=None)

上面例子使用了ConfigParser来读取配置，再用shlex来切割参数。也可以通过fromfile_prefix_chars 告知argparse输入参数为文件。

argparse_fromfile_prefix_chars.py

import argparse
import shlex

parser = argparse.ArgumentParser(description='Short sample app',
                                 fromfile_prefix_chars='@',
                                 )

parser.add_argument('-a', action="store_true", default=False)
parser.add_argument('-b', action="store", dest="b")
parser.add_argument('-c', action="store", dest="c", type=int)

print(parser.parse_args(['@argparse_fromfile_prefix_chars.txt']))

argparse_fromfile_prefix_chars.txt

-a
-b
2

执行结果

$ python3 argparse_fromfile_prefix_chars.py

Namespace(a=True, b='2', c=None)

帮助

• 自动生成

Argparse会自动生成的帮助和版本信息。ArgumentParser的add_help参数控制帮助的生成，默认是开启。

argparse_with_help.py

import argparse

parser = argparse.ArgumentParser(add_help=True)

parser.add_argument('-a', action="store_true", default=False)
parser.add_argument('-b', action="store", dest="b")
parser.add_argument('-c', action="store", dest="c", type=int)

print(parser.parse_args())

下例就关闭帮助：

argparse_without_help.py

import argparse

parser = argparse.ArgumentParser(add_help=False)

parser.add_argument('-a', action="store_true", default=False)
parser.add_argument('-b', action="store", dest="b")
parser.add_argument('-c', action="store", dest="c", type=int)

print(parser.parse_args())

执行结果

$ python argparse_with_help.py -h
usage: argparse_with_help.py [-h] [-a] [-b B] [-c C]
optional arguments:
-h, --help show this help message and exit
-a
-b B
-c C
$ python argparse_without_help.py -h
usage: argparse_without_help.py [-a] [-b B] [-c C]
argparse_without_help.py: error: unrecognized arguments: -h

• 自定义帮助

argparse_custom_help.py

import argparse

parser = argparse.ArgumentParser(add_help=True)

parser.add_argument('-a', action="store_true", default=False)
parser.add_argument('-b', action="store", dest="b")
parser.add_argument('-c', action="store", dest="c", type=int)

print('print_usage output:')
parser.print_usage()
print()

print('print_help output:')
parser.print_help()

执行结果

$ python3 argparse_custom_help.py

print_usage output:
usage: argparse_custom_help.py [-h] [-a] [-b B] [-c C]

print_help output:
usage: argparse_custom_help.py [-h] [-a] [-b B] [-c C]

optional arguments:
  -h, --help  show this help message and exit
  -a
  -b B
  -c C

argparse_raw_description_help_formatter.py

import argparse

parser = argparse.ArgumentParser(
    add_help=True,
    formatter_class=argparse.RawDescriptionHelpFormatter,
    description="""
    description
        not
           wrapped""",
    epilog="""
    epilog
      not
         wrapped""",
)

parser.add_argument(
    '-a', action="store_true",
    help="""argument
    help is
    wrapped
    """,
)

parser.print_help()

执行结果

$ python3 argparse_raw_description_help_formatter.py

usage: argparse_raw_description_help_formatter.py [-h] [-a]

    description
        not
           wrapped

optional arguments:
  -h, --help  show this help message and exit
  -a          argument help is wrapped

    epilog
      not
         wrapped

argparse_raw_text_help_formatter.py

import argparse

parser = argparse.ArgumentParser(
    add_help=True,
    formatter_class=argparse.RawTextHelpFormatter,
    description="""
    description
        not
           wrapped""",
    epilog="""
    epilog
      not
         wrapped""",
)

parser.add_argument(
    '-a', action="store_true",
    help="""argument
    help is not
    wrapped
    """,
)

parser.print_help()

执行结果

$ python3 argparse_raw_text_help_formatter.py

usage: argparse_raw_text_help_formatter.py [-h] [-a]

    description
        not
           wrapped

optional arguments:
  -h, --help  show this help message and exit
  -a          argument
                  help is not
                  wrapped


    epilog
      not
         wrapped

argparse_metavar_type_help_formatter.py

import argparse

parser = argparse.ArgumentParser(
    add_help=True,
    formatter_class=argparse.MetavarTypeHelpFormatter,
)

parser.add_argument('-i', type=int, dest='notshown1')
parser.add_argument('-f', type=float, dest='notshown2')

parser.print_help()

执行结果

$ python3 argparse_metavar_type_help_formatter.py

usage: argparse_metavar_type_help_formatter.py [-h] [-i int] [-f
 float]

optional arguments:
  -h, --help  show this help message and exit
  -i int
  -f float

组织解析器

公共解析器:通过父子类来实现。

见argparse_parent_base.py：

import argparse

parser = argparse.ArgumentParser(add_help=False)

parser.add_argument('--user', action="store")
parser.add_argument('--password', action="store")

argparse_uses_parent.py

import argparse
import argparse_parent_base

parser = argparse.ArgumentParser(
    parents=[argparse_parent_base.parser],
)

parser.add_argument('--local-arg',
                    action="store_true",
                    default=False)

print(parser.parse_args())

注意：父类关闭了help。子类却默认开启了help。执行结果：

$ python3 argparse_uses_parent.py -h

usage: argparse_uses_parent.py [-h] [--user USER]
                               [--password PASSWORD]
                               [--local-arg]

optional arguments:
  -h, --help           show this help message and exit
  --user USER
  --password PASSWORD
  --local-arg

参数冲突

argparse_conflict_handler_resolve.py

import argparse

parser = argparse.ArgumentParser(conflict_handler='resolve')

parser.add_argument('-a', action="store")
parser.add_argument('-b', action="store", help='Short alone')
parser.add_argument('--long-b', '-b',
                    action="store",
                    help='Long and short together')

print(parser.parse_args(['-h']))

执行结果

$ python3 argparse_conflict_handler_resolve.py

usage: argparse_conflict_handler_resolve.py [-h] [-a A]
[--long-b LONG_B]

optional arguments:
  -h, --help            show this help message and exit
  -a A
  --long-b LONG_B, -b LONG_B
                        Long and short together

argparse_conflict_handler_resolve2.py、

import argparse

parser = argparse.ArgumentParser(conflict_handler='resolve')

parser.add_argument('-a', action="store")
parser.add_argument('--long-b', '-b',
                    action="store",
                    help='Long and short together')
parser.add_argument('-b', action="store", help='Short alone')

print(parser.parse_args(['-h']))

执行结果

$ python3 argparse_conflict_handler_resolve2.py

usage: argparse_conflict_handler_resolve2.py [-h] [-a A]
                                             [--long-b LONG_B]
                                             [-b B]

optional arguments:
  -h, --help       show this help message and exit
  -a A
  --long-b LONG_B  Long and short together
  -b B             Short alone

参数分组

默认有可选参数和必选参数组。

argparse_default_grouping.py

import argparse

parser = argparse.ArgumentParser(description='Short sample app')

parser.add_argument('--optional', action="store_true",
                    default=False)
parser.add_argument('positional', action="store")

print(parser.parse_args())

执行结果

$ python3 argparse_default_grouping.py -h

usage: argparse_default_grouping.py [-h] [--optional] positional

Short sample app

positional arguments:
  positional

optional arguments:
  -h, --help  show this help message and exit
  --optional

前面的用户名和密码就可以分组：

argparse_parent_with_group.py

import argparse

parser = argparse.ArgumentParser(add_help=False)

group = parser.add_argument_group('authentication')

group.add_argument('--user', action="store")
group.add_argument('--password', action="store")

argparse_uses_parent_with_group.py

import argparse
import argparse_parent_with_group

parser = argparse.ArgumentParser(
    parents=[argparse_parent_with_group.parser],
)

parser.add_argument('--local-arg',
                    action="store_true",
                    default=False)

print(parser.parse_args())

执行结果

$ python3 argparse_uses_parent_with_group.py -h

usage: argparse_uses_parent_with_group.py [-h] [--user USER]
                                          [--password PASSWORD]
                                          [--local-arg]

optional arguments:
  -h, --help           show this help message and exit
  --local-arg

authentication:
  --user USER
  --password PASSWORD

互斥选项

使用add_mutually_exclusive_group()可以添加互斥选项：

argparse_mutually_exclusive.py

import argparse

parser = argparse.ArgumentParser()

group = parser.add_mutually_exclusive_group()
group.add_argument('-a', action='store_true')
group.add_argument('-b', action='store_true')

print(parser.parse_args())

执行结果

$ python3 argparse_mutually_exclusive.py -h

usage: argparse_mutually_exclusive.py [-h] [-a | -b]

optional arguments:
  -h, --help  show this help message and exit
  -a
  -b

$ python3 argparse_mutually_exclusive.py -a

Namespace(a=True, b=False)

$ python3 argparse_mutually_exclusive.py -b

Namespace(a=False, b=True)

$ python3 argparse_mutually_exclusive.py -a -b

usage: argparse_mutually_exclusive.py [-h] [-a | -b]
argparse_mutually_exclusive.py: error: argument -b: not allowed
with argument -a

嵌套解析

argparse_subparsers.py

import argparse

parser = argparse.ArgumentParser()

subparsers = parser.add_subparsers(help='commands')

# A list command
list_parser = subparsers.add_parser(
    'list', help='List contents')
list_parser.add_argument(
    'dirname', action='store',
    help='Directory to list')

# A create command
create_parser = subparsers.add_parser(
    'create', help='Create a directory')
create_parser.add_argument(
    'dirname', action='store',
    help='New directory to create')
create_parser.add_argument(
    '--read-only', default=False, action='store_true',
    help='Set permissions to prevent writing to the directory',
)

# A delete command
delete_parser = subparsers.add_parser(
    'delete', help='Remove a directory')
delete_parser.add_argument(
    'dirname', action='store', help='The directory to remove')
delete_parser.add_argument(
    '--recursive', '-r', default=False, action='store_true',
    help='Remove the contents of the directory, too',
)

print(parser.parse_args())

执行结果

$ python3 argparse_subparsers.py -h

usage: argparse_subparsers.py [-h] {list,create,delete} ...

positional arguments:
  {list,create,delete}  commands
    list                List contents
    create              Create a directory
    delete              Remove a directory

optional arguments:
  -h, --help            show this help message and exit

$ python3 argparse_subparsers.py create -h

usage: argparse_subparsers.py create [-h] [--read-only] dirname

positional arguments:
  dirname      New directory to create

optional arguments:
  -h, --help   show this help message and exit
  --read-only  Set permissions to prevent writing to the directo
ry

$ python3 argparse_subparsers.py delete -r foo

Namespace(dirname='foo', recursive=True)

高级参数处理

可变参数：数字N代表N的参数，？0或者1个参数。*0或者多个参数。+1或者多个参数。

argparse_nargs.py

import argparse

parser = argparse.ArgumentParser()

parser.add_argument('--three', nargs=3)
parser.add_argument('--optional', nargs='?')
parser.add_argument('--all', nargs='*', dest='all')
parser.add_argument('--one-or-more', nargs='+')

print(parser.parse_args())

执行结果

$ python3 argparse_nargs.py -h

usage: argparse_nargs.py [-h] [--three THREE THREE THREE]
                [--optional [OPTIONAL]]
                [--all [ALL [ALL ...]]]
                [--one-or-more ONE_OR_MORE [ONE_OR_MORE ...]]

optional arguments:
  -h, --help            show this help message and exit
  --three THREE THREE THREE
  --optional [OPTIONAL]
  --all [ALL [ALL ...]]
  --one-or-more ONE_OR_MORE [ONE_OR_MORE ...]

$ python3 argparse_nargs.py

Namespace(all=None, one_or_more=None, optional=None, three=None)

$ python3 argparse_nargs.py --three

usage: argparse_nargs.py [-h] [--three THREE THREE THREE]
                [--optional [OPTIONAL]]
                [--all [ALL [ALL ...]]]
                [--one-or-more ONE_OR_MORE [ONE_OR_MORE ...]]
argparse_nargs.py: error: argument --three: expected 3
argument(s)

$ python3 argparse_nargs.py --three a b c

Namespace(all=None, one_or_more=None, optional=None,
three=['a', 'b', 'c'])

$ python3 argparse_nargs.py --optional

Namespace(all=None, one_or_more=None, optional=None, three=None)

$ python3 argparse_nargs.py --optional with_value

Namespace(all=None, one_or_more=None, optional='with_value',
three=None)

$ python3 argparse_nargs.py --all with multiple values

Namespace(all=['with', 'multiple', 'values'], one_or_more=None,
optional=None, three=None)

$ python3 argparse_nargs.py --one-or-more with_value

Namespace(all=None, one_or_more=['with_value'], optional=None,
three=None)

$ python3 argparse_nargs.py --one-or-more with multiple values

Namespace(all=None, one_or_more=['with', 'multiple', 'values'],
optional=None, three=None)

$ python3 argparse_nargs.py --one-or-more

usage: argparse_nargs.py [-h] [--three THREE THREE THREE]
                [--optional [OPTIONAL]]
                [--all [ALL [ALL ...]]]
                [--one-or-more ONE_OR_MORE [ONE_OR_MORE ...]]
argparse_nargs.py: error: argument --one-or-more: expected
at least one argument

参数类型

argparse_type.py

import argparse

parser = argparse.ArgumentParser()

parser.add_argument('-i', type=int)
parser.add_argument('-f', type=float)
parser.add_argument('--file', type=open)

try:
    print(parser.parse_args())

except IOError as msg:
    parser.error(str(msg))

执行结果

$ python3 argparse_type.py -i 1

Namespace(f=None, file=None, i=1)

$ python3 argparse_type.py -f 3.14

Namespace(f=3.14, file=None, i=None)

$ python3 argparse_type.py --file argparse_type.py

Namespace(f=None, file=<_io.TextIOWrapper
name='argparse_type.py' mode='r' encoding='UTF-8'>, i=None)

$ python3 argparse_type.py -i a

usage: argparse_type.py [-h] [-i I] [-f F] [--file FILE]
argparse_type.py: error: argument -i: invalid int value: 'a'

$ python3 argparse_type.py -f 3.14.15

usage: argparse_type.py [-h] [-i I] [-f F] [--file FILE]
argparse_type.py: error: argument -f: invalid float value:
'3.14.15'

$ python3 argparse_type.py --file does_not_exist.txt

usage: argparse_type.py [-h] [-i I] [-f F] [--file FILE]
argparse_type.py: error: [Errno 2] No such file or directory:
'does_not_exist.txt'

Choices可以指定参数的选项：

argparse_choices.py

import argparse

parser = argparse.ArgumentParser()

parser.add_argument(
    '--mode',
    choices=('read-only', 'read-write'),
)

print(parser.parse_args())

执行结果

$ python3 argparse_choices.py -h

usage: argparse_choices.py [-h] [--mode {read-only,read-write}]

optional arguments:
  -h, --help            show this help message and exit
  --mode {read-only,read-write}

$ python3 argparse_choices.py --mode read-only

Namespace(mode='read-only')

$ python3 argparse_choices.py --mode invalid

usage: argparse_choices.py [-h] [--mode {read-only,read-write}]
argparse_choices.py: error: argument --mode: invalid choice:
'invalid' (choose from 'read-only', 'read-write')

文件参数

argparse_FileType.py

import argparse

parser = argparse.ArgumentParser()

parser.add_argument('-i', metavar='in-file',
                    type=argparse.FileType('rt'))
parser.add_argument('-o', metavar='out-file',
                    type=argparse.FileType('wt'))

try:
    results = parser.parse_args()
    print('Input file:', results.i)
    print('Output file:', results.o)
except IOError as msg:
    parser.error(str(msg))

执行结果

$ python3 argparse_FileType.py -h

usage: argparse_FileType.py [-h] [-i in-file] [-o out-file]

optional arguments:
  -h, --help   show this help message and exit
  -i in-file
  -o out-file

$ python3 argparse_FileType.py -i argparse_FileType.py -o tmp_\
file.txt

Input file: <_io.TextIOWrapper name='argparse_FileType.py'
mode='rt' encoding='UTF-8'>
Output file: <_io.TextIOWrapper name='tmp_file.txt' mode='wt'
encoding='UTF-8'>

$ python3 argparse_FileType.py -i no_such_file.txt

usage: argparse_FileType.py [-h] [-i in-file] [-o out-file]
argparse_FileType.py: error: argument -i: can't open
'no_such_file.txt': [Errno 2] No such file or directory:
'no_such_file.txt'

自定义action

自定义action是argparse.Action的子类可以处理add_argument中的参数定义相关的参数，并返回一个可调用对象。构造函数会处理参数定义，仅仅需要处理__call__函数。__call__函数中parser代表解释器，namespace用于返回解释结果，value为要处理的参数，option_string用于触发action（对可选参数，永远是None。

argparse_custom_action.py

import argparse


class CustomAction(argparse.Action):
    def __init__(self,
                 option_strings,
                 dest,
                 nargs=None,
                 const=None,
                 default=None,
                 type=None,
                 choices=None,
                 required=False,
                 help=None,
                 metavar=None):
        argparse.Action.__init__(self,
                                 option_strings=option_strings,
                                 dest=dest,
                                 nargs=nargs,
                                 const=const,
                                 default=default,
                                 type=type,
                                 choices=choices,
                                 required=required,
                                 help=help,
                                 metavar=metavar,
                                 )
        print('Initializing CustomAction')
        for name, value in sorted(locals().items()):
            if name == 'self' or value is None:
                continue
            print('  {} = {!r}'.format(name, value))
        print()
        return

    def __call__(self, parser, namespace, values,
                 option_string=None):
        print('Processing CustomAction for {}'.format(self.dest))
        print('  parser = {}'.format(id(parser)))
        print('  values = {!r}'.format(values))
        print('  option_string = {!r}'.format(option_string))

        # Do some arbitrary processing of the input values
        if isinstance(values, list):
            values = [v.upper() for v in values]
        else:
            values = values.upper()
        # Save the results in the namespace using the destination
        # variable given to our constructor.
        setattr(namespace, self.dest, values)
        print()


parser = argparse.ArgumentParser()

parser.add_argument('-a', action=CustomAction)
parser.add_argument('-m', nargs='*', action=CustomAction)

results = parser.parse_args(['-a', 'value',
                             '-m', 'multivalue',
                             'second'])
print(results)

执行结果

$ python3 argparse_custom_action.py

Initializing CustomAction
  dest = 'a'
  option_strings = ['-a']
  required = False

Initializing CustomAction
  dest = 'm'
  nargs = '*'
  option_strings = ['-m']
  required = False

Processing CustomAction for a
  parser = 4315836992
  values = 'value'
  option_string = '-a'

Processing CustomAction for m
  parser = 4315836992
  values = ['multivalue', 'second']
  option_string = '-m'

Namespace(a='VALUE', m=['MULTIVALUE', 'SECOND'])

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