Support enum param type

[saroad2]

Description

Added a new ability to be able to create a choice parameter type from enum class.

Why not using click.Choice?

click.Choice always returns a string and can't be modified to into any other type. if you try to do that using the callback parameter, it will fail.

On the other hand, enums are the way of python to allow only a finite number of values to be accepted in a given scenario. It seems to me like to logical step that click.Choice should have returned an enum.

Now, using EnumParamType, one can create a choice-like parameter that returns an enum instead of a string.
Moreover, once you add a new value to your enum class, it will automatically update as a valid choice for the paramater type.

[lewoudar]

we probably want to implement __repr__, get_missing_message and shell_complete methods from the click.Choice class

[lewoudar]

Hi @saroad2 , thanks for the proposal.

click.Choice always returns a string and can't be modified to into any other type. if you try to do that using the callback parameter, it will fail.

I was a bit skeptical about this and it works for me unless I don't understand the issue. I'm using click 8.X.X

import enum
import click


class Hash(enum.Enum):
    MD5 = 'MD5'
    SHA1 = 'SHA1'


def convert_to_enum(ctx, param, value):
    if value:
        return Hash[value]


@click.command()
@click.option(
    '--hash-type',
    type=click.Choice(['MD5', 'SHA1'], case_sensitive=False),
    callback=convert_to_enum
)
def cli(hash_type):
    """Test cli"""
    click.echo(hash_type)

Nevertheless, we can still add a native enum type :)
I pointed you to some missing methods to add.

[saroad2]

I was a bit skeptical about this and it works for me unless I don't understand the issue. I'm using click 8.X.X

Oh, that's super weird. For some reason it didn't work for me. I guess I just did something wrong.

If that's so, there are two ways to move forward:

• Use the implementation in this PR and let EnumParamType inherit from CustomParamType
• Let EnumParamType inherit directly from click.Choice and wrap the convert method to return the enum. That will help us avoid rewriting all of click.Choice methods again from scratch.

Both options are valid in my opinion.
If you think the latter is better, I will close this PR and write another one.

[lewoudar]

I think the second approach is better i.e reusing click.Choice as a base.

But ultimetaly, you can directly propose your change on the click project :-)

[saroad2]

I will give it a try.

The people maintaining Click seem to reject most of my ideas.
I'll try make the same PR there. if they approve it, I will remove this PR. If not, I'll create a new PR here.

[lewoudar]

Ack, if you can give me the link to your PR on the click project, I will appreciate :)

So I can also follow the progress.

[saroad2]

Hey, no problem.
Here's the PR pallets/click#2210

[lewoudar]

Thanks