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PEP 827: Switch ParamKind to be a proper enum #4981

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PEP 827: Switch ParamKind to be a proper enum #4981

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50 changes: 24 additions & 26 deletions peps/pep-0827.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -379,29 +379,32 @@ We introduce a ``Param`` type that contains all the information about a function
class Param[
N: str | None,
T,
K: ParamKind = Literal["positional_or_keyword"],
K: ParamKind = Literal[ParamKind.POSITIONAL_OR_KEYWORD],
D = typing.Never,
]:
pass

ParamKind = typing.Literal[
"*", "**", "keyword", "positional", "positional_or_keyword"
]
class ParamKind(enum.IntEnum):
POSITIONAL_ONLY = 0
POSITIONAL_OR_KEYWORD = 1
VAR_POSITIONAL = 2
KEYWORD_ONLY = 3
VAR_KEYWORD = 4

type PosParam[T] = Param[None, T, Literal["positional"]]
type PosDefaultParam[T] = Param[None, T, Literal["positional"], T]
type DefaultParam[N: str, T] = Param[N, T, Literal["positional_or_keyword"], T]
type NamedParam[N: str, T] = Param[N, T, Literal["keyword"]]
type NamedDefaultParam[N: str, T] = Param[N, T, Literal["keyword"], T]
type ArgsParam[T] = Param[None, T, Literal["*"]]
type KwargsParam[T] = Param[None, T, Literal["**"]]
type PosParam[T] = Param[None, T, Literal[ParamKind.POSITIONAL_ONLY]]
type PosDefaultParam[T] = Param[None, T, Literal[ParamKind.POSITIONAL_ONLY], T]
type DefaultParam[N: str, T] = Param[N, T, Literal[ParamKind.POSITIONAL_OR_KEYWORD], T]
type NamedParam[N: str, T] = Param[N, T, Literal[ParamKind.KEYWORD_ONLY]]
type NamedDefaultParam[N: str, T] = Param[N, T, Literal[ParamKind.KEYWORD_ONLY], T]
type ArgsParam[T] = Param[None, T, Literal[ParamKind.VAR_POSITIONAL]]
type KwargsParam[T] = Param[None, T, Literal[ParamKind.VAR_KEYWORD]]


The argument ``K``, of type ``ParamKind``, represents the parameter
kind of the parameter, and defaults to the ordinary
``Literal["positional_or_keyword"]``. It is an error to create
``Callable`` with a ``Param`` containing multiple kinds unioned
together.
``Literal[ParamKind.POSITIONAL_OR_KEYWORD]``. ``ParamKind`` mirrors
``inspect._ParameterKind``. It is an error to create ``Callable``
with a ``Param`` containing multiple kinds unioned together.

The argument ``D`` carries the type of the parameter's default, if one
exists, and is ``Never`` otherwise. When the default value is a
Expand Down Expand Up @@ -438,13 +441,13 @@ as::

Callable[
Params[
Param[Literal["a"], int, Literal["positional"]],
Param[Literal["a"], int, Literal[ParamKind.POSITIONAL_ONLY]],
Param[Literal["b"], int],
Param[Literal["c"], int, Literal["positional_or_keyword"], Literal[0]],
Param[None, int, Literal["*"]],
Param[Literal["d"], int, Literal["keyword"]],
Param[Literal["e"], int, Literal["keyword"], Literal[0]],
Param[None, int, Literal["**"]],
Param[Literal["c"], int, Literal[ParamKind.POSITIONAL_OR_KEYWORD], Literal[0]],
Param[None, int, Literal[ParamKind.VAR_POSITIONAL]],
Param[Literal["d"], int, Literal[ParamKind.KEYWORD_ONLY]],
Param[Literal["e"], int, Literal[ParamKind.KEYWORD_ONLY], Literal[0]],
Param[None, int, Literal[ParamKind.VAR_KEYWORD]],
],
int,
]
Expand Down Expand Up @@ -1124,7 +1127,7 @@ based on iterating over all attributes.
p.name,
p.type,
# All arguments are keyword-only
Literal["keyword"],
Literal[ParamKind.KEYWORD_ONLY],
# GetDefault is Never when there's no default, so use it
# directly as D.
GetDefault[p.init],
Expand Down Expand Up @@ -1903,11 +1906,6 @@ Open Issues
``readonly`` had been added as a parameter to ``TypedDict`` we would
use that, but it wasn't.

* :ref:`Extended Callables <pep827-extended-callables-prereq>`: Currently the
qualifiers are short strings for code brevity, but an alternate approach
would be to mirror ``inspect.Signature`` more directly, and have an enum
with names like ``ParamKind.POSITIONAL_OR_KEYWORD``. Would that be better?

* :ref:`Members <pep827-members>`: Should ``Members`` return all
methods, even those without annotations? We excluded them out of the
desire for some consistency with attributes, but it would not be
Expand Down
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