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

日期：2018-08-20点击：482收藏

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'])