Sourced from mypy's changelog.

Mypy Release Notes

Mypy 1.9

We’ve just uploaded mypy 1.9 to the Python Package Index (PyPI). Mypy is a static type checker for Python. This release includes new features, performance improvements and bug fixes. You can install it as follows:

python3 -m pip install -U mypy

You can read the full documentation for this release on Read the Docs.

Breaking Changes

Because the version of typeshed we use in mypy 1.9 doesn't support 3.7, neither does mypy 1.9. (Jared Hance, PR 16883)

We are planning to enable local partial types (enabled via the --local-partial-types flag) later this year by default. This change was announced years ago, but now it's finally happening. This is a major backward-incompatible change, so we'll probably include it as part of the upcoming mypy 2.0 release. This makes daemon and non-daemon mypy runs have the same behavior by default.

Local partial types can also be enabled in the mypy config file:

local_partial_types = True

We are looking at providing a tool to make it easier to migrate projects to use --local-partial-types, but it's not yet clear whether this is practical. The migration usually involves adding some explicit type annotations to module-level and class-level variables.

Basic Support for Type Parameter Defaults (PEP 696)

This release contains new experimental support for type parameter defaults (PEP 696). Please try it out! This feature was contributed by Marc Mueller.

Since this feature will be officially introduced in the next Python feature release (3.13), you will need to import TypeVar, ParamSpec or TypeVarTuple from typing_extensions to use defaults for now.

This example adapted from the PEP defines a default for BotT:

from typing import Generic
from typing_extensions import TypeVar
class Bot: ...
BotT = TypeVar("BotT", bound=Bot, default=Bot)
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• 5ff46f8 Remove dev.
• 155909a [Release 1.9] Unsupport targetting 3.7. (#16883) (#16900)
• 6615cab [Release 1.9] Stubtest: ignore a new protocol dunder (#16895) (#16899)
• b956e6a stubtest: Private parameters can be omitted (#16507)
• ede0b20 Bump ruff to 0.2.0 (#16870)
• 7bdd61f stubgen: Fix crash on star unpack of TypeVarTuple (#16869)
• 8c2ef9d Update hashes in sync-typeshed.py following recent typeshed sync
• 0dd4b6f Revert use of ParamSpec for functools.wraps
• dd12a2d Revert typeshed ctypes change
• d132999 Revert sum literal integer change (#13961)
• Additional commits viewable in compare view

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