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Fix noncommutative joins with bounded TypeVars (Shantanu, PR 20345)
Respect output format for cached runs by serializing raw errors in cache metas (Ivan Levkivskyi, PR 20372)
Allow types.NoneType in match cases (A5rocks, PR 20383)
Fix mypyc generator regression with empty tuple (BobTheBuidler, PR 20371)
Fix crash involving Unpack-ed TypeVarTuple (Shantanu, PR 20323)
Fix crash on star import of redefinition (Ivan Levkivskyi, PR 20333)
Fix crash on typevar with forward ref used in other module (Ivan Levkivskyi, PR 20334)
Fail with an explicit error on PyPy (Ivan Levkivskyi, PR 20389)

`v1.19.0`

`v1.18.2`

Fix crash on recursive alias (Ivan Levkivskyi, PR 19845)
Add additional guidance for stubtest errors when runtime is object.__init__ (Stephen Morton, PR 19733)
Fix handling of None values in f-string expressions in mypyc (BobTheBuidler, PR 19846)

`v1.18.1`

We’ve just uploaded mypy 1.18.1 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.

Mypy Performance Improvements

Mypy 1.18.1 includes numerous performance improvements, resulting in about 40% speedup
compared to 1.17 when type checking mypy itself. In extreme cases, the improvement
can be 10x or higher. The list below is an overview of the various mypy optimizations.
Many mypyc improvements (discussed in a separate section below) also improve performance.

Type caching optimizations have a small risk of causing regressions. When
reporting issues with unexpected inferred types, please also check if
--disable-expression-cache will work around the issue, as it turns off some of
these optimizations.

Improve self check performance by 1.8% (Jukka Lehtosalo, PR 19768, 19769, 19770)
Optimize fixed-format deserialization (Ivan Levkivskyi, PR 19765)
Use macros to optimize fixed-format deserialization (Ivan Levkivskyi, PR 19757)
Two additional micro‑optimizations (Ivan Levkivskyi, PR 19627)
Another set of micro‑optimizations (Ivan Levkivskyi, PR 19633)
Cache common types (Ivan Levkivskyi, PR 19621)
Skip more method bodies in third‑party libraries for speed (Ivan Levkivskyi, PR 19586)
Simplify the representation of callable types (Ivan Levkivskyi, PR 19580)
Add cache for types of some expressions (Ivan Levkivskyi, PR 19505)
Use cache for dictionary expressions (Ivan Levkivskyi, PR 19536)
Use cache for binary operations (Ivan Levkivskyi, PR 19523)
Cache types of type objects (Ivan Levkivskyi, PR 19514)
Avoid duplicate work when checking boolean operations (Ivan Levkivskyi, PR 19515)
Optimize generic inference passes (Ivan Levkivskyi, PR 19501)
Speed up the default plugin (Jukka Lehtosalo, PRs 19385 and 19462)
Remove nested imports from the default plugin (Ivan Levkivskyi, PR 19388)
Micro‑optimize type expansion (Jukka Lehtosalo, PR 19461)
Micro‑optimize type indirection (Jukka Lehtosalo, PR 19460)
Micro‑optimize the plugin framework (Jukka Lehtosalo, PR 19464)
Avoid temporary set creation in subtype checking (Jukka Lehtosalo, PR 19463)
Subtype checking micro‑optimization (Jukka Lehtosalo, PR 19384)
Return early where possible in subtype check (Stanislav Terliakov, PR 19400)
Deduplicate some types before joining (Stanislav Terliakov, PR 19409)
Speed up type checking by caching argument inference context (Jukka Lehtosalo, PR 19323)
Optimize binding method self argument type and deprecation checks (Ivan Levkivskyi, PR 19556)
Keep trivial instance types/aliases during expansion (Ivan Levkivskyi, PR 19543)

Fixed‑Format Cache (Experimental)

Mypy now supports a new cache format used for faster incremental builds. It makes
incremental builds up to twice as fast. The feature is experimental and
currently only supported when using a compiled version of mypy. Use --fixed-format-cache
to enable the new format, or fixed_format_cache = True in a configuration file.

We plan to enable this by default in a future mypy release, and we'll eventually
deprecate and remove support for the original JSON-based format.

Unlike the JSON-based cache format, the new binary format is currently
not easy to parse and inspect by mypy users. We are planning to provide a tool to
convert fixed-format cache files to JSON, but details of the output JSON may be
different from the current JSON format. If you rely on being able to inspect
mypy cache files, we recommend creating a GitHub issue and explaining your use
case, so that we can more likely provide support for it. (Using
MypyFile.read(binary_data) to inspect cache data may be sufficient to support
some use cases.)

This feature was contributed by Ivan Levkivskyi (PR 19668, 19735, 19750, 19681, 19752, 19815).

Flexible Variable Definitions: Update

Mypy 1.16.0 introduced --allow-redefinition-new, which allows redefining variables
with different types, and inferring union types for variables from multiple assignments.
The feature is now documented in the --help output, but the feature is still experimental.

We are planning to enable this by default in mypy 2.0, and we will also deprecate the
older --allow-redefinition flag. Since the new behavior differs significantly from
the older flag, we encourage users of --allow-redefinition to experiment with
--allow-redefinition-new and create a GitHub issue if the new functionality doesn't
support some important use cases.

This feature was contributed by Jukka Lehtosalo.

Inferred Type for Bare ClassVar

A ClassVar without an explicit type annotation now causes the type of the variable
to be inferred from the initializer:

from typing import ClassVar

class Item:

### Type of 'next_id' is now 'int' (it was 'Any')
    next_id: ClassVar = 1

    ...

This feature was contributed by Ivan Levkivskyi (PR 19573).

Disjoint Base Classes (@disjoint_base, PEP 800)

Mypy now understands disjoint bases (PEP 800): it recognizes the @disjoint_base
decorator, and rejects class definitions that combine mutually incompatible base classes,
and takes advantage of the fact that such classes cannot exist in reachability and
narrowing logic.

This class definition will now generate an error:

Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

If you want to rebase/retry this PR, check this box

This PR was generated by Mend Renovate. View the repository job log.

sonarqubecloud · 2024-04-24T14:51:26Z

Quality Gate passed

See analysis details on SonarCloud

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

sonarqubecloud · 2024-08-24T23:30:04Z

Quality Gate passed

See analysis details on SonarCloud

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

sonarqubecloud · 2024-10-23T00:30:32Z

Quality Gate passed

See analysis details on SonarCloud

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

sonarqubecloud · 2024-12-30T20:08:44Z

Quality Gate passed

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

sonarqubecloud · 2025-02-05T10:53:45Z

Quality Gate passed

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

sonarqubecloud · 2025-08-07T11:40:35Z

Quality Gate passed

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

sonarqubecloud · 2025-09-19T02:43:01Z

Quality Gate passed

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

sonarqubecloud · 2025-12-15T12:20:00Z

Quality Gate passed

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

sonarqubecloud · 2026-02-02T19:52:28Z

Quality Gate passed

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code