Support dict for SelectForm.choices

[marksteward]

A list of tuples made sense before dicts were ordered by default, but we're now already using dicts for optgroup support. It'd be nice to be able to do:

class PastebinEntry(Form):
    language = SelectField(
        'Programming Language',
        choices={
            'cpp': 'C++',
            'py': 'Python',
            'text': 'Plain Text',
        },
    )

form = PastebinEntry()
del form.choices['cpp']  # instead of having to iterate over .choices and filter out 'cpp'

This could still coexist with an optgroup version:

class PastebinEntry(Form):
    language = SelectField(
        'Programming Language',
        choices={
            'Actual languages': {'cpp': 'C++', 'py': 'Python'},
            'Generic': {'text': 'Plain Text'},
        },
    )

or the current allowed format:

class PastebinEntry(Form):
    language = SelectField(
        'Programming Language',
        choices={
            'Actual languages': [('cpp', 'C++'), ('py', 'Python')],
            'Generic': [('text', 'Plain Text')],
        },
    )

Happy to provide a PR if this sounds sensible!

[marksteward]

I'll take that as PR not welcome, then.

[azmeuk]

Hi,
Thank you for your suggestion and sorry for not having answered it.
dicts indeed appears more elegant than lists of tuples we use to have, #889 (re)introduced a specialized Choice dataclass which goes further than dict can, for instance by supporting render_kw.
Giving it a second thought, that would probably not be incompatible with choice dicts, but I wonder if we want to support several APIs for choices.

[azmeuk]

For the record, I added support for dict choices in #923