使用argparse作为无前缀的强制参数 [英] Using argparse for mandatory argument without prefix

问题描述

我正在尝试在python应用程序中使用argparse模块. 我的应用程序应使用不带任何前缀的单个强制性参数运行.我想不出办法.

I'm trying to use argparse module within my python application. My application should be run with single mandatory argument without any prefixes. I could not come up with a way to do it.

推荐答案

下面是一个使用argparse精确地要求一个整数参数的简单示例:

Here is a simple example using argparse to require exactly one integer argument:

import argparse

parser = argparse.ArgumentParser(description='process an integer')
parser.add_argument('integer', metavar='N', type=int, nargs=1,
               help='an integer')
args = parser.parse_args()
print(args.integer)

将这段代码保存在argparse1.py中并运行它可以得到:

Saving this code in argparse1.py and running it gives:

$ python argparse1.py 5
[5]  

$ python argparse1.py
usage: argparse1.py [-h] N
argpars1.py: error: the following arguments are required: N

$ python argparse1.py 5 7
usage: argparse1.py [-h] N
argparse1.py: error: unrecognized arguments: 7

$ python argparse1.py test
usage: argparse1.py N
argparse1.py: error: argument N: invalid int value: 'test'

$ python argparse1.py -h
usage: argparse1.py [-h] N

process an integer

positional arguments:
  N           an integer

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

要删除可选参数，请使用add_help = False定义ArgumentParser，如下所示:

To remove the optional arguments define ArgumentParser with add_help=False as follows:

import argparse

parser = argparse.ArgumentParser(add_help=False)
parser.add_argument('integer', metavar='N', type=int, nargs=1)
args = parser.parse_args()
print(args.integer)

将此代码放入argparse2.py中并对其进行测试即可得出:

Putting this code in argparse2.py and testing it gives:

$ python argparse2.py
usage: argparse2.py N
argparse2.py: error: the following arguments are required: N

$ python argparse2.py 5
[5]

$ python argparse2.py 5 7
usage: argparse2.py N
argparse2.py: error: unrecognized arguments: 7

$ python argparse2.py hello
usage: argparse2.py N
argparse2.py: error: argument N: invalid int value: 'hello'

$ python argparse2.py -h
usage: argparse2.py N
argparse2.py: error: the following arguments are required: N

可以通过导入argparse.SUPPRESS并使用用法= SUPPRESS配置ArgumentParser来抑制所有使用情况消息，如下所示:

All usage messages can be suppressed by importing argparse.SUPPRESS and configuring ArgumentParser with usage=SUPPRESS as follows:

from argparse import ArgumentParser,SUPPRESS

parser = ArgumentParser(add_help=False, usage=SUPPRESS)
parser.add_argument('integer', metavar='N', type=int, nargs=1)
args = parser.parse_args()
print(args.integer)

将此代码保存在argparse3.py中并运行它可以得到:

Saving this code in argparse3.py and running it gives:

$ python argparse3.py 5
[5]

$ python argparse3.py 5 7 9
argparse3.py: error: unrecognized arguments: 7 9

$ python argparse3.py -h
argparse3.py: error: the following arguments are required: N

无法识别的参数"错误在ArgumentParser.parse_args()中硬编码(

The "unrecognized arguments" error is hardcoded in ArgumentParser.parse_args() (https://hg.python.org/cpython/file/3.4/Lib/argparse.py#l1727) and the "following arguments are required" error is separately hardcoded (https://hg.python.org/cpython/file/3.4/Lib/argparse.py#l1994) both without recourse to modification from the API. The latter appears to be in _parse_known_args(self, arg_strings, namespace) that I suppose could be overridden but would involve copying about 250 lines of code in order to modify 1 line to change that error message.

但是，可以通过仅添加一个带有nargs ='*'且不带类型的参数来避免这些错误消息，这有效地允许所有命令行，然后添加自定义的参数错误处理，包括您自己的错误和用法消息.例如:

However, it is possible to avoid these error messages by adding just one argument with nargs='*' and no type, which effectively allows all command lines, and then adding custom error handling of arguments including your own error and usage messages. For example:

import os
import sys
from argparse import ArgumentParser,SUPPRESS

script =  os.path.basename(sys.argv[0])
usage = 'usage: ' + script + ' n (int)'

parser = ArgumentParser(add_help=False, usage=SUPPRESS)
parser.add_argument('integer', nargs='*')
args = parser.parse_args()

if (len(args.integer) == 0):
    print('error: no argument provided\n', usage, file=sys.stderr, sep = '')
    sys.exit(1)


if (len(args.integer) > 1):
    print('error: too many arguments\n', usage, file=sys.stderr, sep = '')
    sys.exit(1)

v = args.integer[0]

try:
    v = int(v)
except ValueError:
    print("error: '", v, "'", ' is not an integer\n', usage, file=sys.stderr, sep='')
    sys.exit(1)

print(v + 2)

将此代码放在argparse4.py中并对其进行测试即可得出:

Putting this code in argparse4.py and testing it gives:

$ python argparse4.py 5
7

$ python argparse4.py
error: no argument provided
usage: argparse4.py n (int)

$ python argparse4.py 5 9
error: too many arguments
usage: argparse4.py n (int)

$ python argparse4.py hello
error: 'hello' is not an integer
usage: argparse4.py n (int)

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