如何在Python argparse中生成带换行的多行示例命令？

我编写了名为dd.py的Python脚本，使用argparse库实现命令行参数解析。我定义了包含5条CAZyme注释相关示例命令的字符串example_commands，并将其作为argparse.ArgumentParser的description参数。期望执行python dd.py --help时，这些示例命令能按设定的换行格式清晰显示，但实际输出中所有示例命令的换行失效，内容被拼接在一起。

脚本代码 #

import argparse

## Define the command line arguments

example_commands='''Example commands:\n
1. CAZyme annotation with isolated genome sequence as input \n
run_dbcan EscheriaColiK12MG1655.fna prok \n
2. CAZyme annotation with isolated protein sequence as input \n
run_dbcan EscheriaColiK12MG1655.faa protein \n
3. CAZyme annotation with meta genome as input \n
run_dbcan EscheriaColiK12MG1655.fna meta \n
4. CAZyme and CGC annotation with meta genome as input \n
run_dbcan EscheriaColiK12MG1655.fna meta -c EscheriaColiK12MG1655.gff \n
5. CAZyme, CGC annotation and substrate prediction with meta genome as input \n
run_dbcan EscheriaColiK12MG1655.fna meta -c EscheriaColiK12MG1655.gff --cgc_substrate \n'''

parser = argparse.ArgumentParser(description=example_commands)
parser.add_argument('input_file', help='Input file path')
parser.add_argument('input_type', choices=['prok', 'protein', 'meta'], help='Input type (prok, protein, or meta)')
parser.add_argument('-c', '--gff_file', help='GFF file path')
parser.add_argument('--cgc_substrate', action='store_true', help='Enable substrate prediction')

# Parse the command line arguments and display the help message
args = parser.parse_args()

预期输出 #

(base) ➜  ~ python dd.py --help
usage: dd.py [-h] [-c GFF_FILE] [--cgc_substrate] input_file {prok,protein,meta}

Example commands: 
1. CAZyme annotation with isolated genome sequence as input run_dbcan EscheriaColiK12MG1655.fna prok 
2. CAZyme annotation with isolated protein
sequence as input 
run_dbcan EscheriaColiK12MG1655.faa protein 
3. CAZyme annotation with meta genome as input 
run_dbcan EscheriaColiK12MG1655.fna meta 
4. CAZyme and CGC annotation with meta genome as input 
run_dbcan EscheriaColiK12MG1655.fna meta -c EscheriaColiK12MG1655.gff 
5. CAZyme, CGC annotation and substrate prediction with meta genome as input 
run_dbcan EscheriaColiK12MG1655.fna meta -c EscheriaColiK12MG1655.gff --cgc_substrate

positional arguments:
  input_file            Input file path
  {prok,protein,meta}   Input type (prok, protein, or meta)

optional arguments:
  -h, --help            show this help message and exit
  -c GFF_FILE, --gff_file GFF_FILE
                        GFF file path
  --cgc_substrate       Enable substrate prediction

实际输出 #

(base) ➜  ~ python dd.py --help
usage: dd.py [-h] [-c GFF_FILE] [--cgc_substrate] input_file {prok,protein,meta}

Example commands: 1. CAZyme annotation with isolated genome sequence as input run_dbcan EscheriaColiK12MG1655.fna prok 2. CAZyme annotation with isolated protein
sequence as input run_dbcan EscheriaColiK12MG1655.faa protein 3. CAZyme annotation with meta genome as input run_dbcan EscheriaColiK12MG1655.fna meta 4. CAZyme and CGC
annotation with meta genome as input run_dbcan EscheriaColiK12MG1655.fna meta -c EscheriaColiK12MG1655.gff 5. CAZyme, CGC annotation and substrate prediction with meta
genome as input run_dbcan EscheriaColiK12MG1655.fna meta -c EscheriaColiK12MG1655.gff --cgc_substrate

positional arguments:
  input_file            Input file path
  {prok,protein,meta}   Input type (prok, protein, or meta)

optional arguments:
  -h, --help            show this help message and exit
  -c GFF_FILE, --gff_file GFF_FILE
                        GFF file path
  --cgc_substrate       Enable substrate prediction

解决办法 #

argparse默认的HelpFormatter会自动对description文本重新排版，把所有连续空白（包括换行）都替换成单个空格，导致你的换行失效。解决方法是使用RawDescriptionHelpFormatter类，它会完全保留你定义的原始文本格式：

修改解析器的初始化代码，添加formatter_class参数：

parser = argparse.ArgumentParser(description=example_commands, formatter_class=argparse.RawDescriptionHelpFormatter)

替换后再执行python dd.py --help，示例命令就会按照你设定的换行格式显示了。

内容的提问来源于stack exchange，提问作者Lena