python - 将 click.MultiCommand 与类方法一起使用

Question

如何click.MultiCommand与定义为类方法的命令一起使用？

我正在尝试为转换器设置一个插件系统，库的用户可以在其中提供自己的转换器。对于这个系统，我正在设置一个 CLI，如下所示：

$ myproj convert {converter} INPUT OUTPUT {ARGS}

每个转换器都是它自己的类，并且都继承自BaseConverter. 其中BaseConverter是最简单的 Click 命令，它只接受输入和输出。

对于不需要更多的转换器，他们不必重写该方法。如果转换器需要更多，或者需要提供额外的文档，那么它需要被覆盖。

使用下面的代码，尝试使用 cli 时出现以下错误：

类型错误：cli() 缺少 1 个必需的位置参数：'cls'

conversion/

├── __init__.py
└── backends/
    ├── __init__.py
    ├── base.py
    ├── bar.py
    ├── baz.py
    └── foo.py

# cli.py

from pydoc import locate
import click
from proj.conversion import AVAILABLE_CONVERTERS

class ConversionCLI(click.MultiCommand):
    def list_commands(self, ctx):
        return sorted(list(AVAILABLE_CONVERTERS))

    def get_command(self, ctx, name):
        return locate(AVAILABLE_CONVERTERS[name] + '.cli')


@click.command(cls=ConversionCLI)
def convert():
    """Convert files using specified converter"""
    pass

# conversion/__init__.py

from django.conf import settings

AVAILABLE_CONVERTERS = {
    'bar': 'conversion.backends.bar.BarConverter',
    'baz': 'conversion.backends.baz.BazConverter',
    'foo': 'conversion.backends.foo.FooConverter',
}

extra_converters = getattr(settings, 'CONVERTERS', {})
AVAILABLE_CONVERTERS.update(extra_converters)

# conversion/backends/base.py

import click

class BaseConverter():
    @classmethod
    def convert(cls, infile, outfile):
        raise NotImplementedError

    @classmethod
    @click.command()
    @click.argument('infile')
    @click.argument('outfile')
    def cli(cls, infile, outfile):
        return cls.convert(infile, outfile)

# conversion/backends/bar.py

from proj.conversion.base import BaseConverter

class BarConverter(BaseConverter):
    @classmethod
    def convert(cls, infile, outfile):
        # do stuff

# conversion/backends/foo.py

import click
from proj.conversion.base import BaseConverter

class FooConverter(BaseConverter):
    @classmethod
    def convert(cls, infile, outfile, extra_arg):
        # do stuff

    @classmethod
    @click.command()
    @click.argument('infile')
    @click.argument('outfile')
    @click.argument('extra-arg')
    def cli(cls, infile, outfile, extra_arg):
        return cls.convert(infile, outfile, extra_arg)

标签： pythoncommand-line-interfacepython-click

Answer 1

要将 aclassmethod用作单击命令，您需要能够cls在调用命令时填充参数。这可以通过自定义click.Command类来完成，例如：

自定义类：

import click

class ClsMethodClickCommand(click.Command):
    def __init__(self, *args, **kwargs):
        self._cls = [None]
        super(ClsMethodClickCommand, self).__init__(*args, **kwargs)

    def main(self, *args, **kwargs):
        self._cls[0] = args[0]
        return super(ClsMethodClickCommand, self).main(*args[1:], **kwargs)

    def invoke(self, ctx):
        ctx.params['cls'] = self._cls[0]
        return super(ClsMethodClickCommand, self).invoke(ctx)

使用自定义类：

class MyClassWithAClickCommand:

    @classmethod
    @click.command(cls=ClsMethodClickCommand)
    ....
    def cli(cls, ....):
        ....

然后在click.Multicommand类中您需要填充_cls属性，因为command.main在这种情况下不会调用：

def get_command(self, ctx, name):
    # this is hard coded in this example but presumably
    #   would be done with a lookup via name
    cmd = MyClassWithAClickCommand.cli

    # Tell the click command which class it is associated with
    cmd._cls[0] = MyClassWithAClickCommand
    return cmd

这是如何运作的？

这是因为 click 是一个设计良好的 OO 框架。@click.command()装饰器通常实例化一个对象click.Command，但允许使用cls参数覆盖此行为。因此，从click.Command我们自己的类中继承并覆盖所需的方法是一件相对容易的事情。

在这种情况下，我们覆盖click.Command.invoke()然后将包含类添加到ctx.params字典中，就像cls调用命令处理程序之前一样。

测试代码：

class MyClassWithAClickCommand:

    @classmethod
    @click.command(cls=ClsMethodClickCommand)
    @click.argument('arg')
    def cli(cls, arg):
        click.echo('cls: {}'.format(cls.__name__))
        click.echo('cli: {}'.format(arg))


class ConversionCLI(click.MultiCommand):
    def list_commands(self, ctx):
        return ['converter_x']

    def get_command(self, ctx, name):
        cmd = MyClassWithAClickCommand.cli
        cmd._cls[0] = MyClassWithAClickCommand
        return cmd


@click.command(cls=ConversionCLI)
def convert():
    """Convert files using specified converter"""



if __name__ == "__main__":
    commands = (
        'converter_x an_arg',
        'converter_x --help',
        'converter_x',
        '--help',
        '',
    )

    import sys, time

    time.sleep(1)
    print('Click Version: {}'.format(click.__version__))
    print('Python Version: {}'.format(sys.version))
    for cmd in commands:
        try:
            time.sleep(0.1)
            print('-----------')
            print('> ' + cmd)
            time.sleep(0.1)
            convert(cmd.split())

        except BaseException as exc:
            if str(exc) != '0' and \
                    not isinstance(exc, (click.ClickException, SystemExit)):
                raise

结果：

Click Version: 6.7
Python Version: 3.6.3 (v3.6.3:2c5fed8, Oct  3 2017, 18:11:49) [MSC v.1900 64 bit (AMD64)]
-----------
> converter_x an_arg
class: MyClassWithAClickCommand
cli: an_arg
-----------
> converter_x --help
Usage: test.py converter_x [OPTIONS] ARG

Options:
  --help  Show this message and exit.
-----------
> converter_x
Usage: test.py converter_x [OPTIONS] ARG

Error: Missing argument "arg".
-----------
> --help
Usage: test.py [OPTIONS] COMMAND [ARGS]...

  Convert files using specified converter

Options:
  --help  Show this message and exit.

Commands:
  converter_x
-----------
> 
Usage: test.py [OPTIONS] COMMAND [ARGS]...

  Convert files using specified converter

Options:
  --help  Show this message and exit.

Commands:
  converter_x