将 argparse 用于没有前缀的强制参数 [英] Using argparse for mandatory argument without prefix

问题描述

我正在尝试在我的 Python 应用程序中使用 argparse 模块.我的应用程序应该使用没有任何前缀的单个强制参数运行.我想不出办法来做到这一点.

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

这是一个使用 argparse 来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)

将此代码保存在 argparse1.py 中并运行它会得到:

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 并对其进行测试:

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usage=SUPPRESS 配置 ArgumentParser 来抑制所有使用消息，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 中并运行它会得到:

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() (https://hg.python.org/cpython/file/3.4/Lib/argparse.py#l1727)和需要以下参数"错误是单独硬编码的(https://hg.python.org/cpython/file/3.4/Lib/argparse.py#l1994) 两者都不需要从 API 中进行修改.后者似乎在 _parse_known_args(self, arg_strings, namespace) 中，我认为它可以被覆盖，但将涉及复制大约 250 行代码以修改 1 行以更改该错误消息.

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，可以通过只添加一个 nargs='*' 且没有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，然后添加自定义错误处理参数，包括您自己的错误和使用消息.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)

将此代码放入 argparse4.py 并对其进行测试:

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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