Better structure dataset implementations

The suggestion is to adjust all the datasets (e.g. speechcommands) to follow some changes done in tedlium, see example below.

• Add a _parse_filesystem method to extract a list of “data point identifiers” in a pre-determined order to replace the generic walk_files, as here and #791.
• Move _load_item as method, as here.
• Replace class attributes by constructor arguments, e.g. here.
• Remove non-standard attributes, e.g. here? or add attributes, e.g. here?

Relates to #852, GTZAN #791, tedlium #882. cc @mthrok @cpuhrsch

[mthrok]

@krishnakalyan3

Thanks for the feedback. Do you have any other thoughts while working on #1127?

1. removing _ext_audio -> I will replace it with a string.

Do you mean string “constant”? I think that makes sense, especially for “.wav” formats.

1. deprecating and removing folder_in_archive -> I am also in favor of this, It can also simplify the dataset module in the future.

Yes. We had to do this with CommonVoice recently, and the resulting code became much simple.

1. What about deprecating and removing url?

For url, even though it is rarely used, there are multiple potential scenarios where the source becomes unavailable and the archive is re-hosted somewhere else.

1. firewalls
2. the original source becomes unavailable.

Modifying _RELEASE_CONFIGS directly would be a better option

But there are cases that users do not have an admin privilege to modify the installed package, so it’s better if users can provide their configuration from their client code. Maybe not as a single variable but making a custom configuration type that is specific to the dataset might be a possible option.

[mthrok]

Looking at #1127 (thanks @krishnakalyan3 ), the folder_in_archive should be deprecated and removed, from all the Dataset implementation.

It does not provide consistent behavior with download + extract behavior and, in the first place, directory structure being changed is not something library should be expecting and conforming. If user has changed the directory structure, that’s on the user, and library should not be taking care of it.