"""Human-readable descriptions"""

from __future__ import annotations

from typing import Any

__all__ = [

"Description",

"is_description",

"register_description",

"unregister_description",

]

class Description:

"""Type checker for human-readable descriptions.

By default, only ordinary strings are accepted as descriptions,

but you can register() other classes that will also be allowed,

e.g. to support lazy string objects that are evaluated only at runtime.

If you register(object), any object will be allowed as description.

"""

bases: type | tuple[type, ...] = str

@classmethod

def isinstance(cls, obj: Any) -> bool:

"""Check whether this is an instance of a description."""

return isinstance(obj, cls.bases)

@classmethod

def register(cls, base: type) -> None:

"""Register a class that shall be accepted as a description."""

if not isinstance(base, type):

msg = "Only types can be registered."

raise TypeError(msg)

if base is object:

cls.bases = object

elif cls.bases is object:

cls.bases = base

elif not isinstance(cls.bases, tuple):

if base is not cls.bases:

cls.bases = (cls.bases, base)

elif base not in cls.bases:

cls.bases += (base,)

@classmethod

def unregister(cls, base: type) -> None:

"""Unregister a class that shall no more be accepted as a description."""

if not isinstance(base, type):

msg = "Only types can be unregistered."

raise TypeError(msg)

if isinstance(cls.bases, tuple):

if base in cls.bases: # pragma: no branch

cls.bases = tuple(b for b in cls.bases if b is not base)

if not cls.bases:

cls.bases = object

elif len(cls.bases) == 1:

cls.bases = cls.bases[0]

elif cls.bases is base:

cls.bases = object

is_description = Description.isinstance

register_description = Description.register

unregister_description = Description.unregister