more

Author: hauntsaninja

CHANGELOG.md

@@ -11,12 +11,36 @@ enum members must be left unannotated.
 class Pet(Enum):
     CAT = 1  # Member attribute
     DOG = 2  # Member attribute
-    # WOLF = ...  # The "..." placeholder can be used in type stubs
+    WOLF: int = 3  # New error: Enum members must be left unannotated
 
     species: str  # Considered a non-member attribute
 ```
 
-Contributed by Terence Honles in PR [17207](https://github.com/python/mypy/pull/17207).
+In particular, the specification change can result in issues in type stubs (`.pyi` files), since
+historically it was common to leave the value absent:
+
+```python
+# In a type stub (.pyi file)
+
+class Pet(Enum):
+    # Change in semantics: previously considered members, now non-member attributes
+    CAT: int
+    DOG: int
+
+    # Mypy will now issue a warning if it detects this situation in type stubs:
+    # Detected an enum in a type stub with zero members.
+    # There is a chance this is due to a recent change in the semantics of enum membership.
+    # If so, use `member = value` to mark an enum member, instead of `member: type
+
+class Pet(Enum):
+    # As per the specification, you should now do one of the following:
+    DOG = 1  # Member attribute with value 1 and known type
+    WOLF = cast(int, ...)  # Member attribute with unknown value but known type
+    LION = ...  # Member attribute with unknown value and unknown type
+```
+
+Contributed by Terence Honles in PR [17207](https://github.com/python/mypy/pull/17207) and
+Shantanu Jain in PR [18068](https://github.com/python/mypy/pull/18068).
 
 ## Mypy 1.13
 

mypy/checker.py

@@ -2603,7 +2603,7 @@ def check_enum(self, defn: ClassDef) -> None:
                 self.fail(
                     "Detected an enum in a type stub with zero members. "
                     "There is a chance this is due to a recent change in the semantics of "
-                    "enum membership. If so, use `member = ...` to mark an enum member, "
+                    "enum membership. If so, use `member = value` to mark an enum member, "
                     "instead of `member: type`",
                     defn,
                 )

mypy/test/teststubtest.py

@@ -1318,7 +1318,7 @@ def baz(x: Flags3 | None = ...) -> None: ...
             """,
             runtime="""
             class Flags3(enum.Flag):
-                a = ...
+                a = 1
                 b = 2
             def baz(x=Flags3(0)): pass
             """,
@@ -1897,7 +1897,7 @@ def test_good_literal(self) -> Iterator[Case]:
 
             import enum
             class Color(enum.Enum):
-                RED: int
+                RED = ...
 
             NUM: Literal[1]
             CHAR: Literal['a']

test-data/unit/check-enum.test

@@ -1788,7 +1788,7 @@ import lib
 
 [file lib.pyi]
 from enum import Enum
-class A(Enum):  # E: Detected an enum in a type stub with zero members. There is a chance this is due to a recent change in the semantics of enum membership. If so, use `member = ...` to mark an enum member, instead of `member: type` \
+class A(Enum):  # E: Detected an enum in a type stub with zero members. There is a chance this is due to a recent change in the semantics of enum membership. If so, use `member = value` to mark an enum member, instead of `member: type` \
                 # N: See https://typing.readthedocs.io/en/latest/spec/enums.html#defining-members
     x: int
 class B(A):  # E: Cannot extend enum with existing members: "A"
@@ -1797,7 +1797,7 @@ class B(A):  # E: Cannot extend enum with existing members: "A"
 class C(Enum):
     x = 1
 class D(C):  # E: Cannot extend enum with existing members: "C" \
-             # E: Detected an enum in a type stub with zero members. There is a chance this is due to a recent change in the semantics of enum membership. If so, use `member = ...` to mark an enum member, instead of `member: type` \
+             # E: Detected an enum in a type stub with zero members. There is a chance this is due to a recent change in the semantics of enum membership. If so, use `member = value` to mark an enum member, instead of `member: type` \
              # N: See https://typing.readthedocs.io/en/latest/spec/enums.html#defining-members
     x: int   # E: Cannot assign to final name "x"
 [builtins fixtures/bool.pyi]