Practical tips for parsing Python command line parameters

Practical tips for parsing Python command line parameters

When writing scripts in Python, you often need to obtain parameters from the command line. Python's built-in argparse module provides a simple and powerful tool for command line argument parsing. This article will introduce the basic usage of argparse and provide some practical tips and code examples.

Basic usage

First, you need to import the argparse module:

import argparse

Then, you can create an argparse.ArgumentParser object to Parsing command line parameters:

parser = argparse.ArgumentParser(description='命令行参数解析示例')

description parameter is used to provide a brief description for display in the help message.

Next, you can add different command line arguments to the ArgumentParser object. For example, adding a positional parameter:

parser.add_argument('input_file', help='输入文件路径')

This creates a positional parameter named input_file that specifies the path to the input file.

To provide more flexibility, optional parameters can be added. For example, add a --output parameter to specify the path of the output file:

parser.add_argument('--output', help='输出文件路径')

Use the long parameter form --output, you can also use the short The word form, such as -o. To add the short form of an argument, you can add -o to the argument's dest argument:

parser.add_argument('-o', '--output', help='输出文件路径')

Then, you can use parse_args()Method to parse command line parameters:

args = parser.parse_args()

The parsing results will be saved in the args object. These values ​​can be accessed through the object's properties:

print(args.input_file)
print(args.output)

For positional parameters, you can use the nargs parameter to specify that multiple values ​​are accepted. For example, to accept multiple input file paths, you can use nargs=' ':

parser.add_argument('input_files', nargs='+', help='输入文件路径')

Practical Tips

1. Adding a default value

works Provide default values ​​for parameters. For example, to set the default value of the --output parameter to output.txt:

parser.add_argument('--output', default='output.txt', help='输出文件路径')

If --output## is not specified on the command line #parameter, the default value will be used.

2. Add restrictions

You can add restrictions to parameters. For example, you can use the

choices parameter to specify that a parameter can only accept specific values:

parser.add_argument('--mode', choices=['A', 'B', 'C'], help='运行模式')

Only when the value of the

--mode parameter is A, B or C will be accepted.

3. Add mutually exclusive parameters

Sometimes, you need to ensure that certain parameters are mutually exclusive. A mutually exclusive parameter group can be created using the

add_mutually_exclusive_group() method. For example, to ensure that only one of the --input and --output parameters can be selected, you can do this:

group = parser.add_mutually_exclusive_group()
group.add_argument('--input', help='输入文件路径')
group.add_argument('--output', help='输出文件路径')

4. Add subcommand

Sometimes, you may want to add multiple subcommands to the script. This can be achieved using

subparsers. For example, assuming you want your script to have a run subcommand and a test subcommand, you can do this:

subparsers = parser.add_subparsers(dest='command')

run_parser = subparsers.add_parser('run', help='运行程序')
run_parser.add_argument('--input', help='输入文件路径')

test_parser = subparsers.add_parser('test', help='测试程序')
test_parser.add_argument('--input', help='输入文件路径')

Then, after parsing the command line parameters, you can The value of

args.command determines which subcommand to use.

Sample code

The following is a sample code that demonstrates the techniques and usage mentioned above:

import argparse

def main(args):
    print('输入文件：', args.input_file)
    print('输出文件：', args.output)

    if args.input_files:
        print('输入文件列表：', args.input_files)

    if args.mode:
        print('运行模式：'， args.mode)

    if args.command == 'run':
        print('运行程序')
    elif args.command == 'test':
        print('测试程序')

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='命令行参数解析示例')

    parser.add_argument('input_file', help='输入文件路径')
    parser.add_argument('--output', default='output.txt', help='输出文件路径')
    parser.add_argument('-o', '--output', help='输出文件路径')
    parser.add_argument('input_files', nargs='+', help='输入文件路径')
    parser.add_argument('--mode', choices=['A', 'B', 'C'], help='运行模式')

    subparsers = parser.add_subparsers(dest='command')

    run_parser = subparsers.add_parser('run', help='运行程序')
    run_parser.add_argument('--input', help='输入文件路径')

    test_parser = subparsers.add_parser('test', help='测试程序')
    test_parser.add_argument('--input', help='输入文件路径')

    args = parser.parse_args()
    main(args)

The above is an introduction to practical techniques for Python command line parameter parsing and Sample code.

argparse Provides a flexible and powerful way to parse command line arguments and can be customized according to the needs of the application. Using argparse, you can easily handle various complex command line parameters and improve the scalability and ease of use of your scripts.

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