Make --allow-redefinition mean --allow-redefinition-new#21276
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Make --allow-redefinition mean --allow-redefinition-new#21276
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Looking at the mypy primer output, the results look overall like a net improvement, but supporting # mypy: allow-redefinition
x = None
def f() -> None:
global x
x = 1 # Error if using --allow-redefinition, works otherwisecc @ilevkivskyi in case you have ideas, as you worked on partial types recently |
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IIRC currently we simply disable I don't know what was the motivation for disabling partial |
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Actually after a quick experimentation the other option (allow widening of if name.kind == LDEF:
# TODO: Consider reference to outer function as a different scope?
return False
- elif self.scope.top_level_function() is not None:
+ elif self.scope.top_level_function() is not None and name.kind != GDEF:
# A non-local reference from within a function must refer to a different scope
return True
elif name.kind == GDEF and name.fullname.rpartition(".")[0] != self.tree.fullname:in |
ilevkivskyi
reviewed
Apr 20, 2026
| @@ -1,4 +1,4 @@ | |||
| # mypy: allow-redefinition-new, local-partial-types | |||
| # mypy: allow-redefinition, local-partial-types | |||
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These are actually both enabled in self-check, so this is a no-op.
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I have a variation of this mostly working. It's still a bit tricky, since we need to propagate the widened types to the globals binder, but it seems doable (if a little ugly). |
JukkaL
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Apr 22, 2026
…21285) Now this infers an optional type, for backward compat with `--allow-redefinition-old`: ```py # mypy: allow-redefinition-new x = None def foo() -> None: global x x = 1 # Ok # Type of "x" is "int | None" here ``` There are a few non-trivial things. The implementation propagates the widened type to the global scope, since otherwise `x` would have type `None` at top level after the function. We also only allow widening if the original type is `None`, to make reasoning about this easier. Otherwise the type could be inferred from any number of functions. Also this is sufficient to maintain backward compatibility. I used coding agent assist with small incremental changes and careful manual reviews. See #21276 for additional context.
Contributor
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Diff from mypy_primer, showing the effect of this PR on open source code: spack (https://github.com/spack/spack)
+ lib/spack/spack/llnl/util/filesystem.py:1840: error: Argument 2 to "_log_file_access_issue" has incompatible type "str | Path"; expected "str" [arg-type]
+ lib/spack/spack/llnl/util/filesystem.py:1844: error: Argument 1 to "appendleft" of "deque" has incompatible type "tuple[int, str | Path]"; expected "tuple[int, str]" [arg-type]
+ lib/spack/spack/config.py:486: error: Unused "type: ignore" comment [unused-ignore]
+ lib/spack/spack/util/web.py:83: error: Unused "type: ignore" comment [unused-ignore]
+ lib/spack/spack/spec.py:4298: error: Item "VariantValue" of "Spec | Any | VariantValue" has no attribute "versions" [union-attr]
+ lib/spack/spack/spec.py:4311: error: Item "VariantValue" of "Spec | Any | VariantValue" has no attribute "original_spec_format" [union-attr]
+ lib/spack/spack/url_buildcache.py:1175: error: Need type annotation for "filename_to_mtime" [var-annotated]
+ lib/spack/spack/solver/requirements.py:320: error: Argument 1 to "_parse_and_expand" of "RequirementParser" has incompatible type "Any | list[str]"; expected "str" [arg-type]
+ lib/spack/spack/solver/requirements.py:336: error: Argument "message" to "RequirementRule" has incompatible type "Any | list[str] | None"; expected "str | None" [arg-type]
steam.py (https://github.com/Gobot1234/steam.py)
- steam/id.py:91: error: Incompatible types in assignment (expression has type "int", variable has type "Type | None") [assignment]
- steam/id.py:92: error: Incompatible types in assignment (expression has type "int", variable has type "Universe | None") [assignment]
- steam/id.py:95: error: Incompatible types in assignment (expression has type "int", variable has type "Instance | None") [assignment]
- steam/id.py:97: error: Unsupported operand types for <= ("int" and "None") [operator]
- steam/id.py:97: note: Right operand is of type "Universe | None"
- steam/id.py:97: error: Unsupported operand types for > ("int" and "None") [operator]
- steam/id.py:97: note: Left operand is of type "Universe | None"
- steam/id.py:99: error: Unsupported operand types for <= ("int" and "None") [operator]
- steam/id.py:99: note: Right operand is of type "Type | None"
- steam/id.py:99: error: Unsupported operand types for > ("int" and "None") [operator]
- steam/id.py:99: note: Left operand is of type "Type | None"
- steam/id.py:101: error: Unsupported operand types for <= ("int" and "None") [operator]
- steam/id.py:101: note: Right operand is of type "Instance | None"
- steam/id.py:101: error: Unsupported operand types for > ("int" and "None") [operator]
- steam/id.py:101: note: Left operand is of type "Instance | None"
- steam/id.py:111: error: Unsupported operand types for << ("None" and "int") [operator]
- steam/id.py:111: note: Left operand is of type "Universe | None"
- steam/id.py:111: note: Left operand is of type "Type | None"
- steam/id.py:111: note: Left operand is of type "Instance | None"
- steam/id.py:482: error: Incompatible types in assignment (expression has type "int", variable has type "Instance") [assignment]
- steam/id.py:486: error: Incompatible types in assignment (expression has type "int", variable has type "Instance") [assignment]
- steam/id.py:488: error: Incompatible types in assignment (expression has type "int", variable has type "Instance") [assignment]
- steam/id.py:490: error: Incompatible types in assignment (expression has type "int", variable has type "Instance") [assignment]
- steam/id.py:492: error: Incompatible types in assignment (expression has type "int", variable has type "Instance") [assignment]
+ steam/id.py:494: error: Argument "instance" to "ID" has incompatible type "int"; expected "Instance | None" [arg-type]
- steam/id.py:558: error: Item "None" of "Any | None" has no attribute "get" [union-attr]
- steam/protobufs/struct_messages.py:24: error: Incompatible types in assignment (expression has type "tuple[()]", variable has type "dict[str, Any]") [assignment]
- steam/protobufs/msg.py:229: error: Incompatible types in assignment (expression has type "int", variable has type "EMsg") [assignment]
+ steam/protobufs/msg.py:241: error: Argument 1 to "__init_subclass__" of "MessageMessageBase" has incompatible type "int"; expected "EMsg" [arg-type]
- steam/app.py:388: error: Incompatible types in assignment (expression has type "OwnershipTicket", variable has type "AuthenticationTicket") [assignment]
- steam/app.py:1090: error: Incompatible types in assignment (expression has type "PublishedFile[PartialUser]", variable has type "PublishedFileDetails") [assignment]
- steam/abc.py:211: error: Incompatible types in assignment (expression has type "steam.comment.Comment[Self, PartialUser]", variable has type "steam.protobufs.community.GetCommentThreadResponse.Comment | None") [assignment]
- steam/abc.py:668: error: Unsupported operand types for > ("datetime" and "None") [operator]
- steam/abc.py:668: note: Left operand is of type "datetime | None"
- steam/abc.py:668: error: Unsupported operand types for < ("datetime" and "None") [operator]
- steam/abc.py:668: note: Right operand is of type "datetime | None"
- steam/abc.py:796: error: Incompatible types in assignment (expression has type "PublishedFile[Self]", variable has type "PublishedFileDetails") [assignment]
- steam/gateway.py:830: error: No overload variant of "wait_for" of "SteamWebSocket" matches argument types "int", "Callable[[UnifiedMsgT], bool] | Callable[[Any], Any]" [call-overload]
+ steam/gateway.py:830: error: No overload variant of "wait_for" of "SteamWebSocket" matches argument types "int", "Callable[[UnifiedMsgT], bool]" [call-overload]
- steam/state.py:464: error: Argument 2 to "pop" of "dict" has incompatible type "None"; expected "Clan" [arg-type]
- steam/state.py:1038: error: Incompatible types in assignment (expression has type "Event[EventType, Clan]", variable has type "CMsgClientClanStateEvent") [assignment]
- steam/state.py:1042: error: Incompatible types in assignment (expression has type "Announcement[Clan]", variable has type "CMsgClientClanStateEvent") [assignment]
- steam/state.py:1208: error: Incompatible types in assignment (expression has type "PartialMember | None", variable has type "GroupMember | ClanMember") [assignment]
- steam/state.py:1456: error: Argument 2 to "pop" of "dict" has incompatible type "None"; expected "ClanInvite | GroupInvite" [arg-type]
- steam/state.py:1750: error: Incompatible types in assignment (expression has type "User", variable has type "int") [assignment]
- steam/state.py:1753: error: Incompatible types in assignment (expression has type "int", variable has type "User") [assignment]
- steam/state.py:1754: error: Incompatible types in assignment (expression has type "int", variable has type "User") [assignment]
- steam/state.py:2372: error: Incompatible types in assignment (expression has type "PartialClan", variable has type "PartialUser") [assignment]
- steam/state.py:2374: error: Incompatible types in assignment (expression has type "Event[EventType, PartialClan]", variable has type "PartialUser") [assignment]
- steam/state.py:2376: error: Incompatible types in assignment (expression has type "Announcement[PartialClan]", variable has type "PartialUser") [assignment]
- steam/state.py:2378: error: Incompatible types in assignment (expression has type "PublishedFile[Any | ClientUser | PartialUser] | None", variable has type "PartialUser") [assignment]
- steam/state.py:2383: error: Incompatible types in assignment (expression has type "Review", variable has type "PartialUser") [assignment]
- steam/state.py:2385: error: Incompatible types in assignment (expression has type "Post[PartialUser]", variable has type "PartialUser") [assignment]
- steam/client.py:893: error: Incompatible types in assignment (expression has type "list[GameServer]", variable has type "list[IPsWithSteamIDsResponseServer]") [assignment]
- steam/client.py:1285: error: Incompatible types in assignment (expression has type "float", variable has type "int") [assignment]
- steam/ext/commands/commands.py:285: error: Incompatible types in assignment (expression has type "GroupMixin[Any | None] | Group[CogT, [VarArg(Any), KwArg(Any)], Any] | None", variable has type "Self") [assignment]
+ steam/ext/commands/commands.py:831: error: Incompatible return value type (got "Any | Command[Any, Any, Any]", expected "C") [return-value]
pwndbg (https://github.com/pwndbg/pwndbg)
+ pwndbg/dbg_mod/gdb/__init__.py: note: In member "cast" of class "GDBValue":
+ pwndbg/dbg_mod/gdb/__init__.py:1556: error: Name "type" already defined on line 1554 [no-redef]
+ pwndbg/dbg_mod/gdb/__init__.py: note: At top level:
+ pwndbg/dintegration/__init__.py: note: In member "connect" of class "IntegrationManager":
+ pwndbg/dintegration/__init__.py:509: error: Argument 1 to "DecompilerConnection" has incompatible type "_Method"; expected "ServerProxy" [arg-type]
+ pwndbg/aglib/godbg.py:851: error: Argument 1 to "fmt_bytes" of "FormatOpts" has incompatible type "bytes | bytearray"; expected "bytes" [arg-type]
+ pwndbg/commands/procinfo.py: note: In member "status" of class "Process":
+ pwndbg/commands/procinfo.py:183: error: Argument 1 to "append" of "list" has incompatible type "str"; expected "int" [arg-type]
+ pwndbg/commands/kmod.py: note: In function "kmod":
+ pwndbg/commands/kmod.py:95: error: Argument 2 to "add_symbol_file" of "Process" has incompatible type "object"; expected "int | None" [arg-type]
+ pwndbg/commands/ptmalloc2.py:1589: error: Unused "type: ignore" comment [unused-ignore]
+ pwndbg/dbg_mod/lldb/__init__.py: note: In member "cast" of class "LLDBValue":
+ pwndbg/dbg_mod/lldb/__init__.py:784: error: Name "type" already defined on line 782 [no-redef]
+ pwndbg/dbg_mod/lldb/__init__.py: note: In member "vmmap" of class "LLDBProcess":
+ pwndbg/dbg_mod/lldb/__init__.py:1153: error: Name "pages" already defined on line 1143 [no-redef]
+ pwndbg/dbg_mod/lldb/__init__.py: note: In member "create_value" of class "LLDBProcess":
+ pwndbg/dbg_mod/lldb/__init__.py:1480: error: Name "u64" already defined on line 1476 [no-redef]
+ pwndbg/dbg_mod/lldb/__init__.py: note: In member "arch" of class "LLDBProcess":
+ pwndbg/dbg_mod/lldb/__init__.py:1866: error: Argument "name" to "ArchDefinition" has incompatible type "Any | str"; expected "Literal['x86-64', 'i386', 'i8086', 'mips', 'aarch64', 'arm', 'armcm', 'rv32', 'rv64', 'sparc', 'powerpc', 'loongarch64', 's390x', 'hexagon']" [arg-type]
+ pwndbg/dbg_mod/lldb/repl/__init__.py: note: In function "parse":
+ pwndbg/dbg_mod/lldb/repl/__init__.py:819: error: Need type annotation for "raw" [var-annotated]
+ pwndbg/dbg_mod/lldb/repl/__init__.py: note: At top level:
egglog-python (https://github.com/egraphs-good/egglog-python)
+ python/egglog/ipython_magic.py:41: error: Item "EGraph" of "Any | EGraph" has no attribute "to_graphviz_string" [union-attr]
+ python/egglog/egraph.py:471: error: Unused "type: ignore" comment [unused-ignore]
+ python/egglog/egraph.py:471: error: Item "function" of "Callable[..., Any] | Any" has no attribute "__wrapped__" [union-attr]
+ python/egglog/egraph.py:471: note: Error code "union-attr" not covered by "type: ignore[attr-defined]" comment
Tanjun (https://github.com/FasterSpeeding/Tanjun)
+ tanjun/permissions.py:231: error: Incompatible types in assignment (expression has type "Mapping[Snowflake, Role] | Cache | None", variable has type "Mapping[Snowflake, Role] | None") [assignment]
- tanjun/dependencies/limiters.py:812: error: Incompatible types in assignment (expression has type "_Cooldown", variable has type "AbstractCooldownBucket | None") [assignment]
- tanjun/dependencies/limiters.py:814: error: Item "AbstractCooldownBucket" of "AbstractCooldownBucket | None" has no attribute "check" [union-attr]
- tanjun/dependencies/limiters.py:814: error: Item "None" of "AbstractCooldownBucket | None" has no attribute "check" [union-attr]
- tanjun/dependencies/limiters.py:850: error: Incompatible types in assignment (expression has type "_Cooldown | None", variable has type "AbstractCooldownBucket | None") [assignment]
- tanjun/commands/slash.py:3222: error: Incompatible types in assignment (expression has type "def (AutocompleteContext, float, /, *Any, **Any) -> Coroutine[Any, Any, None] | None", variable has type "def (AutocompleteContext, str, /, *Any, **Any) -> Coroutine[Any, Any, None] | None") [assignment]
- tanjun/commands/slash.py:3225: error: Incompatible types in assignment (expression has type "def (AutocompleteContext, int, /, *Any, **Any) -> Coroutine[Any, Any, None] | None", variable has type "def (AutocompleteContext, str, /, *Any, **Any) -> Coroutine[Any, Any, None] | None") [assignment]
- tanjun/commands/slash.py:3235: error: Argument 1 to "call_with_async_di" of "Context" has incompatible type "def (AutocompleteContext, str, /, *Any, **Any) -> Coroutine[Any, Any, None]"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]" [arg-type]
+ tanjun/commands/slash.py:3235: error: Argument 1 to "call_with_async_di" of "Context" has incompatible type "def (AutocompleteContext, str, /, *Any, **Any) -> Coroutine[Any, Any, None] | def (AutocompleteContext, float, /, *Any, **Any) -> Coroutine[Any, Any, None] | def (AutocompleteContext, int, /, *Any, **Any) -> Coroutine[Any, Any, None]"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]" [arg-type]
pandera (https://github.com/pandera-dev/pandera)
- pandera/engines/utils.py:73: error: Unused "type: ignore[call-overload]" comment [unused-ignore]
+ pandera/engines/utils.py:73: error: Unused "type: ignore[union-attr, call-overload]" comment [unused-ignore]
+ pandera/engines/pandas_engine.py:268: error: Name "pandera_dtype" already defined on line 265 [no-redef]
+ pandera/engines/pandas_engine.py:1457: error: Unused "type: ignore" comment [unused-ignore]
- pandera/typing/pandas.py:211: error: Unused "type: ignore" comment [unused-ignore]
+ pandera/typing/pandas.py:238: error: Unused "type: ignore" comment [unused-ignore]
- pandera/typing/pandas.py:249: error: Unused "type: ignore" comment [unused-ignore]
+ pandera/io/xarray_io.py:248: error: Need type annotation for "data_vars" [var-annotated]
+ pandera/backends/pandas/container.py:774: error: Unused "type: ignore" comment [unused-ignore]
+ pandera/backends/pandas/container.py:776: error: Incompatible return value type (got "T | Any | None", expected "T") [return-value]
- pandera/backends/pandas/array.py:454: error: Incompatible types in assignment (expression has type "str", variable has type "Series[Any] | DataFrame | None") [assignment]
- pandera/backends/pandas/array.py:456: error: Incompatible types in assignment (expression has type "str", variable has type "Series[Any] | DataFrame | None") [assignment]
- pandera/api/pandas/array.py:251: error: Redundant cast to "Series[Any]" [redundant-cast]
+ pandera/io/pandas_io.py:994: error: Incompatible types in assignment (expression has type "dict[str, str]", target has type "str") [assignment]
- pandera/backends/pandas/components.py:980: error: Incompatible types in assignment (expression has type "Hashable", variable has type "str") [assignment]
+ pandera/decorators.py:397: error: Invalid index type "str | int" for "list[Any]"; expected type "SupportsIndex" [index]
+ pandera/decorators.py:401: error: No return value expected [return-value]
+ pandera/api/pandas/model.py:196: error: Unused "type: ignore" comment [unused-ignore]
+ tests/pandas/test_schema_statistics.py:46: error: Unused "type: ignore" comment [unused-ignore]
+ tests/pandas/test_schema_inference.py:26: error: Unused "type: ignore" comment [unused-ignore]
+ pandera/strategies/xarray_strategies.py:297: error: Need type annotation for "coord_specs" [var-annotated]
+ pandera/strategies/xarray_strategies.py:359: error: Need type annotation for "coord_specs" [var-annotated]
+ pandera/api/polars/model.py:82: error: Unused "type: ignore" comment [unused-ignore]
+ pandera/api/ibis/model.py:86: error: Unused "type: ignore" comment [unused-ignore]
|
Collaborator
Author
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The primer looks as expected -- this is mostly an improvement, but a few cases are regressed, notably things like this: def f() -> None:
x: int = 1
print(x)
x: str = "a" # Ok with --allow-redefinition-old but not new
print(x)We could support the above use case by using a variable renaming pass for re-annotated variables, but I'm not sure if this is worth it, as the impact seems fairly small. Also this was false negative ( def f() -> None:
x = None # Now needs type annotation
if int():
x = {}
x["a"] = 1
reveal_type(x) # Now correctly inferred as an optional type |
Member
Yeah, I was thinking about that, and IMO although some users may find that useful it will definitely complicate things. We would need to decide what kind of behavior we want in various edge cases, for example it is not clear whether we need to allow things like this: if foo():
x: int = 1
else:
x: str = "a"and other variations. Also if we will decide to support this at some point, then it will not be a breaking change, so we don't really need to decide now (taking into account that impact for existing users is not too big). |
ilevkivskyi
approved these changes
Apr 22, 2026
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LG, thanks! We will need to emphasize in the CHANGELOG/release notes that only non-annotated variables can be redefined.
We can potentially use the "name" vs "variable" terminology to refer to this in the docs.
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Also now
--allow-redefinitionis the primary flag name for the previous--allow-redefinition-newflag, and the--allow-redefinition-newname is a (soft deprecated) alias.The original
--allow-redefinitionbehavior is still available via--allow-redefinition-old.Also removed some now redundant
--local-partial-typesflags in tests.