python模块介绍- argparse：命令行选项及参数解析

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14.3 argparse：命令行选项及参数解析
作用：命令行选项及参数解析。

Python版本：2.7及以后版本

argparse模块于Python2.7引入，旨在替换optparse。

14.3.1建立解析器
import argparse

parser = argparse.ArgumentParser(

description=’This is a PyMOTW sample program’,

)

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：

import argparse

 

parser = argparse.ArgumentParser(description=’Short sampleapp’)

 

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：

# pythonargparse_short.py

Namespace(a=True, b=’val’, c=3)

 

长参数也可以进行同样处理：

import argparse

 

parser = argparse.ArgumentParser(

description=’Examplewith 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：

# python argparse_long.py

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

 

不同于optparse，argparse可以很好地处理非可选参数（没有’-‘等开头的参数）：

import argparse

 

parser = argparse.ArgumentParser(

description=’Examplewith nonoptional arguments’,

)

 

parser.add_argument(‘count’, action=”store”,type=int)

parser.add_argument(‘units’, action=”store”)

 

print parser.parse_args()

没有指定类型的，默认是字符串。执行结果：

# python argparse_arguments.py 3inches

Namespace(count=3, units=’inches’)

# python argparse_arguments.py some inches

usage: argparse_arguments.py [-h] count units

argparse_arguments.py: error: argument count: invalid intvalue: ‘some’

# python argparse_arguments.py

usage: argparse_arguments.py [-h] count units

argparse_arguments.py: error: too few arguments

 

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：

import argparse

 

parser = argparse.ArgumentParser()

 

parser.add_argument(‘-s’, action=’store’,

dest=’simple_value’,

help=’Storea 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_switch’,

help=’Set a switch to true’)

parser.add_argument(‘-f’, action=’store_false’,

default=False,

dest=’boolean_switch’,

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’ % results.simple_value

print ‘constant_value  = %r’ % results.constant_value

print ‘boolean_switch  = %r’ % results.boolean_switch

print ‘collection      = %r’ % results.collection

print ‘const_collection = %r’ % results.const_collection

执行结果：

# python 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

# python argparse_action.py –version

argparse_action.py 1.0

# python argparse_action.py -s value

simple_value     =’value’

constant_value   = None

boolean_switch   = False

collection       = []

const_collection = []

# python argparse_action.py -c

simple_value     = None

constant_value   =’value-to-store’

boolean_switch   = False

collection       = []

const_collection = []

# python argparse_action.py -t

simple_value     = None

constant_value   = None

boolean_switch   = True

collection       = []

const_collection = []

# python argparse_action.py -f

simple_value     = None

constant_value   = None

boolean_switch   = False

collection       = []

const_collection = []

# python argparse_action.py -a one -a two -a three

simple_value     = None

constant_value   = None

boolean_switch   = False

collection       =[‘one’, ‘two’, ‘three’]

const_collection = []

# python argparse_action.py -B -A

simple_value     = None

constant_value   = None

boolean_switch   = False

collection       = []

const_collection = [‘value-2-to-append’, ‘value-1-to-append’]

 

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。

import argparse

 

parser = argparse.ArgumentParser(

description=’Changethe 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：

root@SZX-SRV-AUTOMATION argparse]# pythonargparse_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

# python argparse_prefix_chars.py +a

Namespace(a=True, noarg=False)

# python argparse_prefix_chars.py -a

Namespace(a=False, noarg=False)

# python argparse_prefix_chars.py //noarg

Namespace(a=None, noarg=True)

# python argparse_prefix_chars.py ++noarg

Namespace(a=None, noarg=True)

# python argparse_prefix_chars.py –noarg

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

argparse_prefix_chars.py: error: unrecognized arguments:–noarg

# python 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：

mport argparse

from ConfigParser import ConfigParser

import shlex

 

parser = argparse.ArgumentParser(description=’Short sampleapp’)

 

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)

执行结果：

# python argparse_with_shlex.py

Config  : -a -b 2

Arg List: [‘-a’, ‘-b’, ‘2’]

Results : Namespace(a=True, b=’2′, c=None)

其中ini文件的内容如下：

# vi argparse_with_shlex.ini

[cli]

options = -a -b 2

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

import argparse

#from ConfigParser import ConfigParser

#import shlex

 

parser = argparse.ArgumentParser(description=’Short sampleapp’,

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’])

执行结果：

# python argparse_fromfile_prefix_chars.py

Namespace(a=True, b=’2′, c=None)

其中argparse_fromfile_prefix_chars.txt文件的内容如下：

# vi argparse_fromfile_prefix_chars.txt

-a

-b

2

 

14.3.2自动生成选项
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。

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：

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

 

版本也可以进行类似的配置：

import argparse

parser = argparse.ArgumentParser(version=’1.0’)

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()

print ’This is not printed’

执行结果：

$ python argparse_with_version.py -h

usage: argparse_with_version.py [-h] [-v] [-a] [-b B] [-c C]

optional arguments:

-h, –help show this help message and exit

-v, –version show program’s version number and exit

-a

-b B

-c C

$ python argparse_with_version.py -v

1.0

$ python argparse_with_version.py –version

1.0

14.3.3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”)

子类：

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：

# python argparse_uses_parent.py -h

usage: argparse_uses_parent.py [-h] [–user USER] [–passwordPASSWORD]

[–local-arg]

 

optional arguments:

-h, –help           show this help message and exit

–user USER

–password PASSWORD

–local-arg

参数分组：默认有可选参数和必选参数组。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”)

子类：

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：

# python 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

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

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：

# python 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

# python argparse_mutually_exclusive.py -a

Namespace(a=True, b=False)

# python argparse_mutually_exclusive.py -b

Namespace(a=False, b=True)

# python argparse_mutually_exclusive.py -a -b

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

argparse_mutually_exclusive.py: error: argument -b: notallowed with argument –a

嵌套解析:

import argparse

 

parser = argparse.ArgumentParser()

 

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

 

# A list command

list_parser = subparsers.add_parser(

‘list’, help=’Listcontents’)

list_parser.add_argument(

‘dirname’,action=’store’,

help=’Directory tolist’)

 

# A create command

create_parser = subparsers.add_parser(

‘create’,help=’Create a directory’)

create_parser.add_argument(

‘dirname’,action=’store’,

help=’New directoryto create’)

create_parser.add_argument(

‘–read-only’,default=False, action=’store_true’,

help=’Setpermissions 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 thecontents of the directory, too’,

)

 

print parser.parse_args()

执行结果：

# python 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

# python 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 thedirectory

# python argparse_subparsers.py delete -r foo

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

14.3.4 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。

import argparse

 

parser = argparse.ArgumentParser()

 

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

 

# A list command

list_parser = subparsers.add_parser(

‘list’, help=’Listcontents’)

list_parser.add_argument(

‘dirname’,action=’store’,

help=’Directory tolist’)

 

# A create command

create_parser = subparsers.add_parser(

‘create’,help=’Create a directory’)

create_parser.add_argument(

‘dirname’,action=’store’,

help=’New directoryto create’)

create_parser.add_argument(

‘–read-only’,default=False, action=’store_true’,

help=’Setpermissions 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 thecontents of the directory, too’,

)

 

print parser.parse_args()

执行结果：

# python 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 THREETHREE

–optional [OPTIONAL]

–all [ALL [ALL …]]

–one-or-moreONE_OR_MORE [ONE_OR_MORE …]

# python argparse_nargs.py

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

# python 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 3argument(s)

# python argparse_nargs.py –three a b c

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

# python argparse_nargs.py –optional

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

# python argparse_nargs.py –optional with_value

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

# python argparse_nargs.py –all with multiple values

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

# python argparse_nargs.py –one-or-more with_value

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

# python 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 atleast one argument

参数类型：

importargparse

 

parser = argparse.ArgumentParser()

 

parser.add_argument(‘-i’, type=int)

parser.add_argument(‘-f’, type=float)

parser.add_argument(‘–file’, type=file)

 

try:

printparser.parse_args()

except IOError, msg:

parser.error(str(msg))

执行结果：

$ python argparse_type.py -i 1

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

$ python argparse_type.py -f 3.14

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

$ python argparse_type.py -i 1

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

$ python argparse_type.py -f 3.14

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

$ python 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’

$ python 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’

$ python 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：

import argparse

 

parser = argparse.ArgumentParser()

 

parser.add_argument(‘–mode’, choices=(‘read-only’,’read-write’))

 

print parser.parse_args()

执行结果：

 

# python 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}

# python argparse_choices.py –mode read-only

Namespace(mode=’read-only’)

# python 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’)

argparse.FileType可以指定文件的模式和buffer：

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 ‘Outputfile:’, results.o

except IOError, msg:

parser.error(str(msg))

执行结果：

# python 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

# python argparse_FileType.py -i argparse_FileType.py -otmp_file.txt

Input file: <open file ‘argparse_FileType.py’, mode ‘rt’ at0xb75923e8>

Output file: <open file ‘tmp_file.txt’, mode ‘wt’ at 0xb75926a8>

# python 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。

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,valuein sorted(locals().items()):

if name ==’self’ or value is None:

continue

print ‘  %s = %r’ % (name, value)

print

return

 

def __call__(self,parser, namespace, values,

option_string=None):

print’Processing CustomAction for “%s”‘ % self.dest

print ‘ parser = %s’ % id(parser)

print ‘  values = %r’ % values

print ‘  option_string = %r’ % option_string

 

# Do somearbitrary processing of the input values

ifisinstance(values, list):

values = [v.upper() for v in values ]

else:

values =values.upper()

# Save theresults in the namespace using the destination

# variable givento 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：

# python 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 = 3076247052

values = ‘value’

option_string = ‘-a’

 

Processing CustomAction for “m”

parser = 3076247052

values =[‘multivalue’, ‘second’]

option_string = ‘-m’

 

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

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