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Enable Mypy strict mode #9803

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64cc758
enable the mypy's strict mode
jorenham Jan 27, 2026
5bc0912
Fix mypy errors
jorenham Jan 27, 2026
8ea699d
Remove python_version mypy configuration; fix issues arising on 3.11-…
akx Jul 21, 2026
7d3a0a3
CI: separate lint + mypy step; run mypy with all supported Python ver…
akx Jul 22, 2026
9dee48c
Bump action versions
akx Aug 16, 2026
0e62d45
Test latest NumPy version on Python > 3.11
radarhere Aug 17, 2026
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3 changes: 2 additions & 1 deletion .ci/requirements-mypy.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,8 @@ arro3-core
IceSpringPySideStubs-PyQt6
IceSpringPySideStubs-PySide6
ipython
numpy==2.4.6
numpy==2.4.6;python_version=="3.11"
numpy;python_version>="3.12"
packaging
pyarrow-stubs
pybind11
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20 changes: 19 additions & 1 deletion .github/workflows/lint.yml
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Expand Up @@ -28,5 +28,23 @@ jobs:
uses: astral-sh/setup-uv@c771a70e6277c0a99b617c7a806ffedaca235ff9 # v9.0.0
- name: Lint
run: uvx --with tox-uv tox -e lint
mypy:
runs-on: ubuntu-latest
strategy:
fail-fast: false
matrix:
python-version: [
"3.14",

@radarhere radarhere Aug 17, 2026

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Note to self - it appears apache/arrow#48172 is blocking 3.15 support

"3.13",
"3.12",
"3.11",
]
name: Mypy
steps:
- uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
with:
persist-credentials: false
- name: Install uv
uses: astral-sh/setup-uv@c771a70e6277c0a99b617c7a806ffedaca235ff9 # v9.0.0
- name: Mypy
run: uvx --with tox-uv tox -e mypy
run: uvx --python=${{ matrix.python-version }} --with tox-uv tox -e mypy
4 changes: 2 additions & 2 deletions Tests/conftest.py
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Expand Up @@ -10,7 +10,7 @@

gil_enabled_at_start = True
if FREE_THREADED_BUILD:
gil_enabled_at_start = sys._is_gil_enabled() # type: ignore[attr-defined]
gil_enabled_at_start = sys._is_gil_enabled() # type: ignore[attr-defined,unused-ignore]


def pytest_report_header(config: pytest.Config) -> str:
Expand All @@ -28,7 +28,7 @@ def pytest_terminal_summary(terminalreporter: pytest.TerminalReporter) -> None:
if (
FREE_THREADED_BUILD
and not gil_enabled_at_start
and sys._is_gil_enabled() # type: ignore[attr-defined]
and sys._is_gil_enabled() # type: ignore[attr-defined,unused-ignore]
):
tr = terminalreporter
tr.ensure_newline()
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12 changes: 5 additions & 7 deletions pyproject.toml
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Expand Up @@ -193,16 +193,14 @@ exclude = [
"^Tests/images/picins/",
"^Tests/images/sunraster/",
]
follow_imports = "silent"
python_version = "3.11"
disallow_any_generics = true
disallow_untyped_defs = true
warn_redundant_casts = true
warn_unused_ignores = true
disallow_subclassing_any = false
disallow_untyped_calls = false
warn_return_any = false
warn_unreachable = true
enable_error_code = "ignore-without-code"
extra_checks = true
strict = true
pretty = true
no_implicit_reexport = false
num_workers = 4

[tool.pytest]
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4 changes: 3 additions & 1 deletion src/PIL/EpsImagePlugin.py
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Expand Up @@ -206,7 +206,9 @@ def _open(self) -> None:
imagedata_size: tuple[int, int] | None = None

byte_arr = bytearray(255)
bytes_mv = memoryview(byte_arr)
# the extra `bytes` annotation here works around several false positive
# `comparison-overlap` mypy errors
bytes_mv: bytes | memoryview = memoryview(byte_arr)
bytes_read = 0
reading_header_comments = True
reading_trailer_comments = False
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5 changes: 3 additions & 2 deletions src/PIL/GifImagePlugin.py
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Expand Up @@ -1195,8 +1195,9 @@ class Collector(BytesIO):
data = []

def write(self, data: Buffer) -> int:
self.data.append(data)
return len(data)
data_bytes = bytes(data)
self.data.append(data_bytes)
return len(data_bytes)

im.load() # make sure raster data is available

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2 changes: 1 addition & 1 deletion src/PIL/ImageGrab.py
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Expand Up @@ -79,7 +79,7 @@ def grab(
scale = 1 if scale_down else 2
im_cropped = im.resize(
((right - left) * scale, (bottom - top) * scale),
box=tuple(coord * 2 for coord in bbox),
box=(left * 2, top * 2, right * 2, bottom * 2),

@hugovk hugovk Sep 1, 2026

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Would you like to either reduce the PR to just this, or split this bit to another PR? I'm happy to merge this.

@radarhere radarhere Sep 1, 2026

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The ImageGrab.py fix is needed for macOS with the current config.

Could you expand on what this means?

@akx akx Sep 1, 2026

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Split out: #9935

@hugovk hugovk Sep 1, 2026

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The ImageGrab.py fix is needed for macOS with the current config.

Could you expand on what this means?

Yep, on main I get:

❯ tox -e mypy
mypy: commands[0]> mypy conftest.py selftest.py setup.py checks docs src winbuild Tests
src/PIL/ImageGrab.py:82: error: Argument "box" to "resize" of "Image" has incompatible
type "tuple[int, ...]"; expected "tuple[float, float, float, float] | None"  [arg-type]
                                box=tuple(coord * 2 for coord in bbox),
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Found 1 error in 1 file (checked 302 source files)
mypy: exit 1 (2.58 seconds) /Users/hugo/github/Pillow> mypy conftest.py selftest.py setup.py checks docs src winbuild Tests pid=84969
  mypy: FAIL code 1 (2.58=setup[0.00]+cmd[2.58] seconds)
  evaluation failed :( (2.63 seconds)

And with #9935:

❯ tox -e mypy
mypy: commands[0]> mypy conftest.py selftest.py setup.py checks docs src winbuild Tests
Success: no issues found in 302 source files
  mypy: OK (2.22=setup[0.00]+cmd[2.22] seconds)
  congratulations :) (2.27 seconds)

@radarhere radarhere Sep 1, 2026

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So why isn't that error appearing in our CI?

@hugovk hugovk Sep 1, 2026 •
edited
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CI runs on Ubuntu and the code in question is macOS-only, gated by if sys.platform == "darwin".

@radarhere radarhere Sep 1, 2026

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Ah, ok, I see.

)
else:
im_cropped = im.crop(bbox)
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