Add GetMember.

Author: dnwpark

pep.rst

@@ -540,6 +540,9 @@ Object inspection
 * ``Attrs[T]``: like ``Members[T]`` but only returns attributes (not
   methods).
 
+* ``GetMember[T, S: Literal[str]]``: Produces a ``Member`` type for the
+  member named ``S`` from the class ``T``.
+
 * ``Member[N: Literal[str], T, Q: MemberQuals, Init, D]``: ``Member``,
   is a simple type, not an operator, that is used to describe members
   of classes.  Its type parameters encode the information about each

tests/test_type_eval.py

@@ -25,6 +25,7 @@
     GenericCallable,
     GetArg,
     GetArgs,
+    GetMember,
     GetMemberType,
     GetName,
     GetType,
@@ -379,6 +380,21 @@ def test_type_from_union_06():
     assert _is_generic_permutation(n, tuple[int, list[IntTree]])
 
 
+def test_getmember_01():
+    d = eval_typing(GetMember[TA, Literal["x"]])
+    assert d == Member[Literal["x"], int, Never, Never, TA]
+    d = eval_typing(GetMemberType[TA, Literal["a"]])
+    assert d == Never
+
+    d = eval_typing(GetMember[TA | TB, Literal["x"]])
+    assert d == (
+        Member[Literal["x"], int, Never, Never, TA]
+        | Member[Literal["x"], str, Never, Never, TB]
+    )
+    d = eval_typing(GetMember[TA | TB, Literal[""]])
+    assert d == Never
+
+
 def test_getarg_never():
     d = eval_typing(GetArg[Never, object, Literal[0]])
     assert d is Never

typemap/type_eval/_eval_operators.py

@@ -25,6 +25,7 @@
     GetAnnotations,
     GetArg,
     GetArgs,
+    GetMember,
     GetMemberType,
     InitField,
     IsSubSimilar,
@@ -657,19 +658,20 @@ def _get_function_hint_namespaces(func, receiver_type=None):
     return globalns, localns
 
 
+def _hint_to_member(n, t, qs, init, d, *, ctx):
+    return Member[
+        typing.Literal[n],
+        _eval_types(t, ctx),
+        _mk_literal_union(*qs),
+        init,
+        d,
+    ]
+
+
 def _hints_to_members(hints, ctx):
     """Convert a hints dictionary to a tuple of Member types."""
     return tuple[
-        *[
-            Member[
-                typing.Literal[n],
-                _eval_types(t, ctx),
-                _mk_literal_union(*qs),
-                init,
-                d,
-            ]
-            for n, (t, qs, init, d) in hints.items()
-        ]
+        *[_hint_to_member(n, *hint, ctx=ctx) for n, hint in hints.items()]
     ]
 
 
@@ -690,6 +692,21 @@ def _eval_Members(tp, *, ctx):
     return _hints_to_members(hints, ctx)
 
 
+@type_eval.register_evaluator(GetMember)
+@_lift_over_unions
+def _eval_GetMember(tp, prop, *, ctx):
+    # XXX: extras?
+    name = _from_literal(prop)
+    hints = {
+        **get_annotated_type_hints(tp, include_extras=True),
+        **get_annotated_method_hints(tp),
+    }
+    if name in hints:
+        return _hint_to_member(name, *hints[name], ctx=ctx)
+    else:
+        return typing.Never
+
+
 ##################################################################
 
 

typemap/typing.py

@@ -131,6 +131,10 @@ class FromUnion[T]:
     pass
 
 
+class GetMember[Lhs, Prop]:
+    pass
+
+
 class GetMemberType[Lhs, Prop]:
     pass