仅当使用click做出选择时才需要和选择

问题描述

使用 click 时，我知道如何定义单选选项.我也知道如何将选项设置为必需.但是，如何可以指示一个选项仅需要如果选项的值是

When using click I know how to define a multiple choice option. I also know how to set an option as a required one. But, how can I indicate that an option B is required only if the value of option A is foo?

这是一个例子:

import click

@click.command()
@click.option('--output',
              type=click.Choice(['stdout', 'file']), default='stdout')
@click.option('--filename', type=click.STRING)
def main(output, filename):
    print("output: " + output)
    if output == 'file':
        if filename is None:
            print("filename must be provided!")
        else:
            print("filename: " + str(filename))

if __name__ == "__main__":
    main()

如果 output 选项是 stdout ，则不需要 filename .但是，如果用户选择 output 作为 file ，则必须提供其他选项 filename .点击是否支持这种模式?

If the output option is stdout, then filename is not needed. However, if the user chooses output to be file, then the other option filename must be provided. Is this pattern supported by click?

在函数的开头，我可以添加以下内容:

At the beginning of the function I can add something like:

if output == 'file' and filename is None:
    raise ValueError('When output is "file", a filename must be provided')

但是我很感兴趣是否有更好/更清洁的解决方案.

But I am interested whether there's a nicer/cleaner solution.

推荐答案

在此示例的特定情况下，我认为一个更简单的方法是摆脱-output ，并简单地假设如果未指定-filename ，并且如果指定了-filename ，则使用 stdout ，而不是 stdout

In the particular case of this example, I think an easier method would be to get rid of --output, and simply assume stdout if --filename is not specified and if --filename is specified, then use it instead of stdout.

但是假设这是一个人为的示例，您可以从 click.Option 继承，以允许连接到点击处理:

But assuming this is a contrived example, you can inherit from click.Option to allow hooking into the click processing:

class OptionRequiredIf(click.Option):

    def full_process_value(self, ctx, value):
        value = super(OptionRequiredIf, self).full_process_value(ctx, value)

        if value is None and ctx.params['output'] == 'file':
            msg = 'Required if --output=file'
            raise click.MissingParameter(ctx=ctx, param=self, message=msg)
        return value

使用自定义类:

要使用自定义类，请将其作为cls参数传递给选项装饰器，例如:

Using Custom Class:

To use the custom class, pass it as the cls argument to the option decorator like:

@click.option('--filename', type=click.STRING, cls=OptionRequiredIf)

测试代码:

import click

@click.command()
@click.option('--output',
              type=click.Choice(['stdout', 'file']), default='stdout')
@click.option('--filename', type=click.STRING, cls=OptionRequiredIf)
def main(output, filename):
    print("output: " + output)
    if output == 'file':
        if filename is None:
            print("filename must be provided!")
        else:
            print("filename: " + str(filename))


main('--output=file'.split())

结果:

Usage: test.py [OPTIONS]

Error: Missing option "--filename".  Required if --output=file

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