Skip to content

Updates to 1.17 changelog #19436

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 3 commits into from
Jul 14, 2025
Merged

Updates to 1.17 changelog #19436

Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
165edbd
Updates to 1.17 changelog
JukkaL Jul 14, 2025
266b644
Don't mark as unreleased
JukkaL Jul 14, 2025
f24ade8
Fix typo
JukkaL Jul 14, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
168 changes: 107 additions & 61 deletions CHANGELOG.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@

## Next Release

## Mypy 1.17 (Unreleased)
## Mypy 1.17

We’ve just uploaded mypy 1.17 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)).
Mypy is a static type checker for Python. This release includes new features and bug fixes.
Expand All @@ -12,11 +12,60 @@ You can install it as follows:

You can read the full documentation for this release on [Read the Docs](http://mypy.readthedocs.io).

### Remove Support for targeting Python 3.8
### Optionally Check That Match Is Exhaustive

Mypy now requires `--python-version 3.9` or greater. Support for only Python 3.8 is
fully removed now. Given an unsupported version, mypy will default to the oldest
supported one, currently 3.9.
Mypy can now optionally generate an error if a match statement does not
match exhaustively, without having to use `assert_never(...)`. Enable
this by using `--enable-error-code exhaustive-match`.

Example:

```python
# mypy: enable-error-code=exhaustive-match

import enum

class Color(enum.Enum):
RED = 1
BLUE = 2

def show_color(val: Color) -> None:
# error: Unhandled case for values of type "Literal[Color.BLUE]"
match val:
case Color.RED:
print("red")
```

This feature was contributed by Donal Burns (PR [19144](https://github.com/python/mypy/pull/19144)).

### Further Improvements to Attribute Resolution

This release includes additional improvements to how attribute types
and kinds are resolved. These fix many bugs and overall improve consistency.

* Handle corner case: protocol/class variable/descriptor (Ivan Levkivskyi, PR [19277](https://github.com/python/mypy/pull/19277))
* Fix a few inconsistencies in protocol/type object interactions (Ivan Levkivskyi, PR [19267](https://github.com/python/mypy/pull/19267))
* Refactor/unify access to static attributes (Ivan Levkivskyi, PR [19254](https://github.com/python/mypy/pull/19254))
* Remove inconsistencies in operator handling (Ivan Levkivskyi, PR [19250](https://github.com/python/mypy/pull/19250))
* Make protocol subtyping more consistent (Ivan Levkivskyi, PR [18943](https://github.com/python/mypy/pull/18943))

### Fixes to Nondeterministic Type Checking

Previous mypy versions could infer different types for certain expressions
across different runs (typically depending on which order certain types
were processed, and this order was nondeterministic). This release includes
fixes to several such issues.

* Fix nondeterministic type checking by making join with explicit Protocol and type promotion commute (Shantanu, PR [18402](https://github.com/python/mypy/pull/18402))
* Fix nondeterministic type checking caused by nonassociative of None joins (Shantanu, PR [19158](https://github.com/python/mypy/pull/19158))
* Fix nondeterministic type checking caused by nonassociativity of joins (Shantanu, PR [19147](https://github.com/python/mypy/pull/19147))
* Fix nondeterministic type checking by making join between `type` and TypeVar commute (Shantanu, PR [19149](https://github.com/python/mypy/pull/19149))

### Remove Support for Targeting Python 3.8

Mypy now requires `--python-version 3.9` or greater. Support for targeting Python 3.8 is
fully removed now. Since 3.8 is an unsupported version, mypy will default to the oldest
supported version (currently 3.9) if you still try to target 3.8.

This change is necessary because typeshed stopped supporting Python 3.8 after it
reached its End of Life in October 2024.
Expand All @@ -27,102 +76,99 @@ Contributed by Marc Mueller
### Initial Support for Python 3.14

Mypy is now tested on 3.14 and mypyc works with 3.14.0b3 and later.
Mypyc compiled wheels of mypy itself will be available for new versions after 3.14.0rc1 is released.
Binary wheels compiled with mypyc for mypy itself will be available for 3.14
some time after 3.14.0rc1 has been released.

Note that not all new features might be supported just yet.
Note that not all features are supported just yet.

Contributed by Marc Mueller (PR [19164](https://github.com/python/mypy/pull/19164))

### Deprecated Flag: \--force-uppercase-builtins
### Deprecated Flag: `--force-uppercase-builtins`

Mypy only supports Python 3.9+. The \--force-uppercase-builtins flag is now deprecated and a no-op. It will be removed in a future version.
Mypy only supports Python 3.9+. The `--force-uppercase-builtins` flag is now
deprecated as unnecessary, and a no-op. It will be removed in a future version.

Contributed by Marc Mueller (PR [19176](https://github.com/python/mypy/pull/19176))

### Mypyc Fixes and Improvements
### Mypyc: Improvements to Generators and Async Functions

This release includes both performance improvements and bug fixes related
to generators and async functions (these share many implementation details).

* Fix exception swallowing in async try/finally blocks with await (Chainfire, PR [19353](https://github.com/python/mypy/pull/19353))
* Fix AttributeError in async try/finally with mixed return paths (Chainfire, PR [19361](https://github.com/python/mypy/pull/19361))
* Derive .c file name from full module name if using multi_file (Jukka Lehtosalo, PR [19278](https://github.com/python/mypy/pull/19278))
* Support overriding the group name used in output files (Jukka Lehtosalo, PR [19272](https://github.com/python/mypy/pull/19272))
* Make generated generator helper method internal (Jukka Lehtosalo, PR [19268](https://github.com/python/mypy/pull/19268))
* Add note about using non-native class to subclass built-in types (Jukka Lehtosalo, PR [19236](https://github.com/python/mypy/pull/19236))
* Make some generated classes implicitly final (Jukka Lehtosalo, PR [19235](https://github.com/python/mypy/pull/19235))
* Free coroutine after await encounters StopIteration (Jukka Lehtosalo, PR [19231](https://github.com/python/mypy/pull/19231))
* Use non-tagged integer for generator label (Jukka Lehtosalo, PR [19218](https://github.com/python/mypy/pull/19218))
* Merge generator and environment classes in simple cases (Jukka Lehtosalo, PR [19207](https://github.com/python/mypy/pull/19207))
* Don't simplify module prefixes if using separate compilation (Jukka Lehtosalo, PR [19206](https://github.com/python/mypy/pull/19206))
* Test function nesting with async functions (Jukka Lehtosalo, PR [19203](https://github.com/python/mypy/pull/19203))

### Mypyc: Partial, Unsafe Support for Free Threading

Mypyc has minimal, quite memory-unsafe support for the free threaded
builds of 3.14. It is also only lightly tested. Bug reports and experience
reports are welcome!

Here are some of the major limitations:
* Free threading only works when compiling a single module at a time.
* If there is concurrent access to an object while another thread is mutating the same
object, it's possible to encounter segfaults and memory corruption.
* There are no efficient native primitives for thread synthronization, though the
regular `threading` module can be used.
* Some workloads don't scale well to multiple threads for no clear reason.

Related PRs:

* Enable partial, unsafe support for free-threading (Jukka Lehtosalo, PR [19167](https://github.com/python/mypy/pull/19167))
* Add comment about incref/decref and free-threaded builds (Jukka Lehtosalo, PR [19155](https://github.com/python/mypy/pull/19155))
* Refactor extension module C generation and generated C (Jukka Lehtosalo, PR [19126](https://github.com/python/mypy/pull/19126))
* Fix incref/decref on free-threaded builds (Jukka Lehtosalo, PR [19127](https://github.com/python/mypy/pull/19127))
* Remove last unreachable block from mypyc code (Stanislav Terliakov, PR [19086](https://github.com/python/mypy/pull/19086))

### Stubgen Improvements
### Other Mypyc Fixes and Improvements

* stubgen: add test case for handling `Incomplete` return types (Alexey Makridenko, PR [19253](https://github.com/python/mypy/pull/19253))
* stubgen: add import for `types` in `__exit__` method signature (Alexey Makridenko, PR [19120](https://github.com/python/mypy/pull/19120))
* stubgenc: add support for including class and property docstrings (Chad Dombrova, PR [17964](https://github.com/python/mypy/pull/17964))
* stubgen: Don't generate `Incomplete | None = None` argument annotation (Sebastian Rittau, PR [19097](https://github.com/python/mypy/pull/19097))
* Support several more constructs in stubgen's AliasPrinter (Stanislav Terliakov, PR [18888](https://github.com/python/mypy/pull/18888))
* Derive .c file name from full module name if using multi_file (Jukka Lehtosalo, PR [19278](https://github.com/python/mypy/pull/19278))
* Support overriding the group name used in output files (Jukka Lehtosalo, PR [19272](https://github.com/python/mypy/pull/19272))
* Add note about using non-native class to subclass built-in types (Jukka Lehtosalo, PR [19236](https://github.com/python/mypy/pull/19236))
* Make some generated classes implicitly final (Jukka Lehtosalo, PR [19235](https://github.com/python/mypy/pull/19235))
* Don't simplify module prefixes if using separate compilation (Jukka Lehtosalo, PR [19206](https://github.com/python/mypy/pull/19206))

### Stubtest Improvements
### Stubgen Improvements

* Syntax error messages capitalization (Charulata, PR [19114](https://github.com/python/mypy/pull/19114))
* Add import for `types` in `__exit__` method signature (Alexey Makridenko, PR [19120](https://github.com/python/mypy/pull/19120))
* Add support for including class and property docstrings (Chad Dombrova, PR [17964](https://github.com/python/mypy/pull/17964))
* Don't generate `Incomplete | None = None` argument annotation (Sebastian Rittau, PR [19097](https://github.com/python/mypy/pull/19097))
* Support several more constructs in stubgen's alias printer (Stanislav Terliakov, PR [18888](https://github.com/python/mypy/pull/18888))

### Miscellaneous Fixes and Improvements

* Combine the revealed types of multiple iteration steps in a more robust manner (Christoph Tyralla, PR [19324](https://github.com/python/mypy/pull/19324))
* Improve the handling of "iteration dependent" errors and notes in finally clauses (Christoph Tyralla, PR [19270](https://github.com/python/mypy/pull/19270))
* Lessen dmypy suggest path limitations for Windows machines (CoolCat467, PR [19337](https://github.com/python/mypy/pull/19337))
* Type ignore comments erroneously marked as unused by dmypy (Charlie Denton, PR [15043](https://github.com/python/mypy/pull/15043))
* Handle corner case: protocol vs classvar vs descriptor (Ivan Levkivskyi, PR [19277](https://github.com/python/mypy/pull/19277))
* Fix `exhaustive-match` error code in title (johnthagen, PR [19276](https://github.com/python/mypy/pull/19276))
* Fix couple inconsistencies in protocols vs TypeType (Ivan Levkivskyi, PR [19267](https://github.com/python/mypy/pull/19267))
* Fix type ignore comments erroneously marked as unused by dmypy (Charlie Denton, PR [15043](https://github.com/python/mypy/pull/15043))
* Fix misspelled `exhaustive-match` error code (johnthagen, PR [19276](https://github.com/python/mypy/pull/19276))
* Fix missing error context for unpacking assignment involving star expression (Brian Schubert, PR [19258](https://github.com/python/mypy/pull/19258))
* Fix and simplify error de-duplication (Ivan Levkivskyi, PR [19247](https://github.com/python/mypy/pull/19247))
* Add regression test for narrowing union of mixins (Shantanu, PR [19266](https://github.com/python/mypy/pull/19266))
* Disallow `ClassVar` in type aliases (Brian Schubert, PR [19263](https://github.com/python/mypy/pull/19263))
* Refactor/unify access to static attributes (Ivan Levkivskyi, PR [19254](https://github.com/python/mypy/pull/19254))
* Clean-up and move operator access to checkmember.py (Ivan Levkivskyi, PR [19250](https://github.com/python/mypy/pull/19250))
* Add script that prints compiled files when self compiling (Jukka Lehtosalo, PR [19260](https://github.com/python/mypy/pull/19260))
* Add script that prints list of compiled files when compiling mypy (Jukka Lehtosalo, PR [19260](https://github.com/python/mypy/pull/19260))
* Fix help message url for "None and Optional handling" section (Guy Wilson, PR [19252](https://github.com/python/mypy/pull/19252))
* Display FQN for imported base classes in errors about incompatible overrides (Mikhail Golubev, PR [19115](https://github.com/python/mypy/pull/19115))
* Fix a minor merge conflict caused by #19118 (Christoph Tyralla, PR [19246](https://github.com/python/mypy/pull/19246))
* Display fully qualified name of imported base classes in errors about incompatible overrides (Mikhail Golubev, PR [19115](https://github.com/python/mypy/pull/19115))
* Avoid false `unreachable`, `redundant-expr`, and `redundant-casts` warnings in loops more robustly and efficiently, and avoid multiple `revealed type` notes for the same line (Christoph Tyralla, PR [19118](https://github.com/python/mypy/pull/19118))
* Fix type extraction from `isinstance` checks (Stanislav Terliakov, PR [19223](https://github.com/python/mypy/pull/19223))
* Erase stray typevars in functools.partial generic (Stanislav Terliakov, PR [18954](https://github.com/python/mypy/pull/18954))
* Make infer_condition_value recognize the whole truth table (Stanislav Terliakov, PR [18944](https://github.com/python/mypy/pull/18944))
* Erase stray type variables in `functools.partial` (Stanislav Terliakov, PR [18954](https://github.com/python/mypy/pull/18954))
* Make inferring condition value recognize the whole truth table (Stanislav Terliakov, PR [18944](https://github.com/python/mypy/pull/18944))
* Support type aliases, `NamedTuple` and `TypedDict` in constrained TypeVar defaults (Stanislav Terliakov, PR [18884](https://github.com/python/mypy/pull/18884))
* Move dataclass kw_only fields to the end of the signature (Stanislav Terliakov, PR [19018](https://github.com/python/mypy/pull/19018))
* Deprecated --force-uppercase-builtins flag (Marc Mueller, PR [19176](https://github.com/python/mypy/pull/19176))
* Provide a better fallback value for the python_version option (Marc Mueller, PR [19162](https://github.com/python/mypy/pull/19162))
* Avoid spurious non-overlapping eq error with metaclass with `__eq__` (Michael J. Sullivan, PR [19220](https://github.com/python/mypy/pull/19220))
* Remove --show-speed-regression in primer (Shantanu, PR [19226](https://github.com/python/mypy/pull/19226))
* Add flag to raise error if match statement does not match exaustively (Donal Burns, PR [19144](https://github.com/python/mypy/pull/19144))
* Narrow type variable bounds in binder (Ivan Levkivskyi, PR [19183](https://github.com/python/mypy/pull/19183))
* Add regression test for dataclass typeguard (Shantanu, PR [19214](https://github.com/python/mypy/pull/19214))
* Move dataclass `kw_only` fields to the end of the signature (Stanislav Terliakov, PR [19018](https://github.com/python/mypy/pull/19018))
* Provide a better fallback value for the `python_version` option (Marc Mueller, PR [19162](https://github.com/python/mypy/pull/19162))
* Avoid spurious non-overlapping equality error with metaclass with `__eq__` (Michael J. Sullivan, PR [19220](https://github.com/python/mypy/pull/19220))
* Narrow type variable bounds (Ivan Levkivskyi, PR [19183](https://github.com/python/mypy/pull/19183))
* Add classifier for Python 3.14 (Marc Mueller, PR [19199](https://github.com/python/mypy/pull/19199))
* Further cleanup after dropping Python 3.8 (Marc Mueller, PR [19197](https://github.com/python/mypy/pull/19197))
* Fix nondeterministic type checking by making join with explicit Protocol and type promotion commute (Shantanu, PR [18402](https://github.com/python/mypy/pull/18402))
* Capitalize syntax error messages (Charulata, PR [19114](https://github.com/python/mypy/pull/19114))
* Infer constraints eagerly if actual is Any (Ivan Levkivskyi, PR [19190](https://github.com/python/mypy/pull/19190))
* Include walrus assignments in conditional inference (Stanislav Terliakov, PR [19038](https://github.com/python/mypy/pull/19038))
* Use PEP 604 syntax for TypeStrVisitor (Marc Mueller, PR [19179](https://github.com/python/mypy/pull/19179))
* Use checkmember.py to check protocol subtyping (Ivan Levkivskyi, PR [18943](https://github.com/python/mypy/pull/18943))
* Update test requirements (Marc Mueller, PR [19163](https://github.com/python/mypy/pull/19163))
* Use more lower case builtins in error messages (Marc Mueller, PR [19177](https://github.com/python/mypy/pull/19177))
* Remove force_uppercase_builtins default from test helpers (Marc Mueller, PR [19173](https://github.com/python/mypy/pull/19173))
* Start testing Python 3.14 (Marc Mueller, PR [19164](https://github.com/python/mypy/pull/19164))
* Use PEP 604 syntax when converting types to strings (Marc Mueller, PR [19179](https://github.com/python/mypy/pull/19179))
* Use more lower-case builtin types in error messages (Marc Mueller, PR [19177](https://github.com/python/mypy/pull/19177))
* Fix example to use correct method of Stack (Łukasz Kwieciński, PR [19123](https://github.com/python/mypy/pull/19123))
* Fix nondeterministic type checking caused by nonassociative of None joins (Shantanu, PR [19158](https://github.com/python/mypy/pull/19158))
* Drop support for --python-version 3.8 (Marc Mueller, PR [19157](https://github.com/python/mypy/pull/19157))
* Fix nondeterministic type checking caused by nonassociativity of joins (Shantanu, PR [19147](https://github.com/python/mypy/pull/19147))
* Fix nondeterministic type checking by making join between TypeType and TypeVar commute (Shantanu, PR [19149](https://github.com/python/mypy/pull/19149))
* Forbid `.pop` of `Readonly` `NotRequired` TypedDict items (Stanislav Terliakov, PR [19133](https://github.com/python/mypy/pull/19133))
* Emit a friendlier warning on invalid exclude regex, instead of a stacktrace (wyattscarpenter, PR [19102](https://github.com/python/mypy/pull/19102))
* Update dmypy/client.py: Enable ANSI color codes for windows cmd (wyattscarpenter, PR [19088](https://github.com/python/mypy/pull/19088))
* Extend special case for context-based typevar inference to typevar unions in return position (Stanislav Terliakov, PR [18976](https://github.com/python/mypy/pull/18976))
* Enable ANSI color codes for dmypy client in Windows (wyattscarpenter, PR [19088](https://github.com/python/mypy/pull/19088))
* Extend special case for context-based type variable inference to unions in return position (Stanislav Terliakov, PR [18976](https://github.com/python/mypy/pull/18976))

### Acknowledgements

Expand Down