fix: use mypy pre-commit in local environment

.github/workflows/check_tpch_queries.yml

@@ -25,7 +25,7 @@ jobs:
           cache-suffix: ${{ matrix.python-version }}
           cache-dependency-glob: "pyproject.toml"
       - name: local-install
-        run: uv pip install -U --pre -e ".[dev, core, dask]" --system
+        run: uv pip install -U --pre -e ".[tests, core, dask]" --system
       - name: generate-data
         run: cd tpch && python generate_data.py
       - name: tpch-tests 

.github/workflows/downstream_tests.yml

@@ -220,7 +220,7 @@ jobs:
         run: |
           cd tea-tasting
           pdm remove narwhals
-          pdm add ./..[dev]
+          pdm add ./..[tests]
       - name: show-deps
         run: |
           cd tea-tasting

.github/workflows/extremes.yml

@@ -28,7 +28,7 @@ jobs:
         run: uv pip install pipdeptree tox virtualenv setuptools pandas==0.25.3 polars==0.20.3 numpy==1.17.5 pyarrow==11.0.0 "pyarrow-stubs<17" scipy==1.5.0 scikit-learn==1.1.0 duckdb==1.0 tzdata --system
       - name: install-reqs
         run: |
-          uv pip install -e ".[dev]" --system
+          uv pip install -e ".[tests]" --system
       - name: show-deps
         run: uv pip freeze
       - name: Assert dependencies
@@ -64,7 +64,7 @@ jobs:
       - name: install-pretty-old-versions
         run: uv pip install pipdeptree tox virtualenv setuptools pandas==1.1.5 polars==0.20.3 numpy==1.17.5 pyarrow==11.0.0 "pyarrow-stubs<17" pyspark==3.5.0 scipy==1.5.0 scikit-learn==1.1.0 duckdb==1.0 tzdata --system
       - name: install-reqs
-        run: uv pip install -e ".[dev]" --system
+        run: uv pip install -e ".[tests]" --system
       - name: show-deps
         run: uv pip freeze
       - name: show-deptree
@@ -103,7 +103,7 @@ jobs:
       - name: install-not-so-old-versions
         run: uv pip install tox virtualenv setuptools pandas==2.0.3 polars==0.20.8 numpy==1.24.4 pyarrow==15.0.0 "pyarrow-stubs<17" pyspark==3.5.0 scipy==1.8.0 scikit-learn==1.3.0 duckdb==1.0 dask[dataframe]==2024.10 tzdata --system
       - name: install-reqs
-        run: uv pip install -e ".[dev]" --system
+        run: uv pip install -e ".[tests]" --system
       - name: show-deps
         run: uv pip freeze
       - name: Assert not so old versions dependencies
@@ -140,7 +140,7 @@ jobs:
           cache-suffix: ${{ matrix.python-version }}
           cache-dependency-glob: "pyproject.toml"
       - name: install-reqs
-        run: uv pip install -e ".[dev]" --system
+        run: uv pip install -e ".[tests]" --system
       - name: install-kaggle
         run: uv pip install kaggle --system
       - name: Download Kaggle notebook artifact

.github/workflows/pytest.yml

@@ -25,7 +25,7 @@ jobs:
           cache-dependency-glob: "pyproject.toml"
       - name: install-reqs
         # Python3.8 is technically at end-of-life, so we don't test everything
-        run: uv pip install -e ".[dev, core]" --system
+        run: uv pip install -e ".[tests, core]" --system
       - name: show-deps
         run: uv pip freeze
       - name: Run pytest
@@ -49,7 +49,7 @@ jobs:
           cache-suffix: ${{ matrix.python-version }}
           cache-dependency-glob: "pyproject.toml"
       - name: install-reqs
-        run: uv pip install -e ".[dev, core, extra, dask, modin]" --system
+        run: uv pip install -e ".[tests, core, extra, dask, modin]" --system
       - name: install pyspark
         run: uv pip install -e ".[pyspark]" --system
         # PySpark is not yet available on Python3.12+
@@ -83,7 +83,7 @@ jobs:
           cache-suffix: ${{ matrix.python-version }}
           cache-dependency-glob: "pyproject.toml"
       - name: install-reqs
-        run: uv pip install -e ".[dev, core, extra, modin, dask]" --system
+        run: uv pip install -e ".[tests, core, extra, modin, dask]" --system
       - name: install pyspark
         run: uv pip install -e ".[pyspark]" --system
         # PySpark is not yet available on Python3.12+

.github/workflows/random_ci_pytest.yml

@@ -27,7 +27,7 @@ jobs:
       - name: install-random-verions
         run: uv pip install -r random-requirements.txt --system
       - name: install-narwhals
-        run: uv pip install -e ".[dev]" --system
+        run: uv pip install -e ".[tests]" --system
       - name: show versions
         run: uv pip freeze
       - name: Run pytest

.github/workflows/typing.yml

@@ -0,0 +1,40 @@
+name: Type checking
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  mypy:
+    strategy:
+      matrix:
+        python-version: ["3.11"]
+        os: [ubuntu-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install uv
+        uses: astral-sh/setup-uv@v5
+        with:
+          enable-cache: "true"
+          cache-suffix: ${{ matrix.python-version }}
+          cache-dependency-glob: "pyproject.toml"
+      - name: Create venv
+        run: uv venv .venv
+      - name: install-reqs
+        # TODO: add more dependencies/backends incrementally
+        run: |
+          source .venv/bin/activate
+          uv pip install -e ".[tests, typing, core]"
+      - name: show-deps
+        run: |
+          source .venv/bin/activate
+          uv pip freeze
+      - name: Run mypy
+        run: |
+          source .venv/bin/activate
+          make typing

.pre-commit-config.yaml

@@ -1,5 +1,6 @@
 ci:
   autoupdate_schedule: monthly
+  skip: [mypy]
 repos:
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
@@ -13,12 +14,6 @@ repos:
     - id: ruff
       alias: check-docstrings
       entry: python utils/check_docstrings.py
-- repo: https://github.com/pre-commit/mirrors-mypy
-  rev: 'v1.14.1'
-  hooks:
-    - id: mypy
-      additional_dependencies: ['polars==1.4.1', 'pytest==8.3.2']
-      files: ^(narwhals|tests)/
 - repo: https://github.com/codespell-project/codespell
   rev: 'v2.4.1'
   hooks:
@@ -84,6 +79,13 @@ repos:
       entry: pull_request_target
       language: pygrep
       files: ^\.github/workflows/
+    - id: mypy
+      name: mypy
+      entry: make typing
+      files: ^(narwhals|tests)/
+      language: system
+      types: [python]
+      require_serial: true
 - repo: https://github.com/adamchainz/blacken-docs
   rev: "1.19.1"  # replace with latest tag on GitHub
   hooks:

Makefile

@@ -0,0 +1,23 @@
+# Mostly based on polars Makefile
+# https://github.com/pola-rs/polars/blob/main/py-polars/Makefile
+
+.DEFAULT_GOAL := help
+
+SHELL=bash
+VENV=./.venv
+
+ifeq ($(OS),Windows_NT)
+	VENV_BIN=$(VENV)/Scripts
+else
+	VENV_BIN=$(VENV)/bin
+endif
+
+
+.PHONY: help
+help:  ## Display this help screen
+	@echo -e "\033[1mAvailable commands:\033[0m"
+	@grep -E '^[a-z.A-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | awk 'BEGIN {FS = ":.*?## "}; {printf "  \033[36m%-22s\033[0m %s\n", $$1, $$2}' | sort
+
+.PHONY: typing
+typing: ## Run typing checks
+	$(VENV_BIN)/mypy

narwhals/_arrow/series.py

@@ -38,6 +38,7 @@
     from narwhals._arrow.namespace import ArrowNamespace
     from narwhals.dtypes import DType
     from narwhals.typing import _1DArray
+    from narwhals.typing import _2DArray
     from narwhals.utils import Version
 
 
@@ -339,7 +340,7 @@ def __getitem__(self: Self, idx: int | slice | Sequence[int]) -> Any | Self:
     def scatter(self: Self, indices: int | Sequence[int], values: Any) -> Self:
         import numpy as np  # ignore-banned-import
 
-        mask = np.zeros(self.len(), dtype=bool)
+        mask: _1DArray = np.zeros(self.len(), dtype=bool)
         mask[indices] = True
         if isinstance(values, self.__class__):
             ser, values = broadcast_and_extract_native(
@@ -726,7 +727,7 @@ def to_dummies(self: Self, *, separator: str, drop_first: bool) -> ArrowDataFram
         name = self._name
         da = series.dictionary_encode(null_encoding="encode").combine_chunks()
 
-        columns = np.zeros((len(da.dictionary), len(da)), np.int8)
+        columns: _2DArray = np.zeros((len(da.dictionary), len(da)), np.int8)
         columns[da.indices, np.arange(len(da))] = 1
         null_col_pa, null_col_pl = f"{name}{separator}None", f"{name}{separator}null"
         cols = [

narwhals/_duckdb/dataframe.py

@@ -159,7 +159,7 @@ def select(
         ):
             return self._from_native_frame(
                 self._native_frame.aggregate(
-                    [val.alias(col) for col, val in new_columns_map.items()]
+                    [val.alias(col) for col, val in new_columns_map.items()]  # type: ignore[arg-type]
                 ),
                 validate_column_names=False,
             )
@@ -482,7 +482,7 @@ def explode(self: Self, columns: list[str]) -> Self:
         original_columns = self.columns
 
         not_null_condition = (
-            col_to_explode.isnotnull() & FunctionExpression("len", col_to_explode) > 0
+            col_to_explode.isnotnull() & FunctionExpression("len", col_to_explode) > 0  # type: ignore[operator]
         )
         non_null_rel = rel.filter(not_null_condition).select(
             *(

narwhals/_duckdb/expr.py

@@ -33,7 +33,7 @@
     from narwhals.utils import Version
 
 
-class DuckDBExpr(CompliantExpr["duckdb.Expression"]):
+class DuckDBExpr(CompliantExpr["duckdb.Expression"]):  # type: ignore[type-var]
     _implementation = Implementation.DUCKDB
     _depth = 0  # Unused, just for compatibility with CompliantExpr
 
@@ -312,13 +312,16 @@ def skew(self: Self) -> Self:
         def func(_input: duckdb.Expression) -> duckdb.Expression:
             count = FunctionExpression("count", _input)
             return CaseExpression(
-                condition=count == 0, value=ConstantExpression(None)
+                condition=count == 0,  # type: ignore[arg-type]
+                value=ConstantExpression(None),
             ).otherwise(
                 CaseExpression(
-                    condition=count == 1, value=ConstantExpression(float("nan"))
+                    condition=count == 1,  # type: ignore[arg-type]
+                    value=ConstantExpression(float("nan")),
                 ).otherwise(
                     CaseExpression(
-                        condition=count == 2, value=ConstantExpression(0.0)
+                        condition=count == 2,  # type: ignore[arg-type]
+                        value=ConstantExpression(0.0),
                     ).otherwise(FunctionExpression("skewness", _input))
                 )
             )
@@ -427,7 +430,7 @@ def _std(_input: duckdb.Expression, ddof: int) -> duckdb.Expression:
             return (
                 FunctionExpression("stddev_pop", _input)
                 * FunctionExpression("sqrt", n_samples)
-                / (FunctionExpression("sqrt", (n_samples - ddof)))
+                / (FunctionExpression("sqrt", (n_samples - ddof)))  # type: ignore[operator]
             )
 
         return self._from_call(
@@ -440,7 +443,7 @@ def _std(_input: duckdb.Expression, ddof: int) -> duckdb.Expression:
     def var(self: Self, ddof: int) -> Self:
         def _var(_input: duckdb.Expression, ddof: int) -> duckdb.Expression:
             n_samples = FunctionExpression("count", _input)
-            return FunctionExpression("var_pop", _input) * n_samples / (n_samples - ddof)
+            return FunctionExpression("var_pop", _input) * n_samples / (n_samples - ddof)  # type: ignore[operator]
 
         return self._from_call(
             _var,
@@ -521,7 +524,7 @@ def fill_null(self: Self, value: Any, strategy: Any, limit: int | None) -> Self:
     def cast(self: Self, dtype: DType | type[DType]) -> Self:
         def func(_input: duckdb.Expression) -> duckdb.Expression:
             native_dtype = narwhals_to_native_dtype(dtype, self._version)
-            return _input.cast(native_dtype)
+            return _input.cast(native_dtype)  # type: ignore[arg-type]
 
         return self._from_call(
             func,

narwhals/_duckdb/expr_dt.py

@@ -60,23 +60,23 @@ def second(self: Self) -> DuckDBExpr:
     def millisecond(self: Self) -> DuckDBExpr:
         return self._compliant_expr._from_call(
             lambda _input: FunctionExpression("millisecond", _input)
-            - FunctionExpression("second", _input) * 1_000,
+            - FunctionExpression("second", _input) * 1_000,  # type: ignore[operator]
             "millisecond",
             expr_kind=self._compliant_expr._expr_kind,
         )
 
     def microsecond(self: Self) -> DuckDBExpr:
         return self._compliant_expr._from_call(
             lambda _input: FunctionExpression("microsecond", _input)
-            - FunctionExpression("second", _input) * 1_000_000,
+            - FunctionExpression("second", _input) * 1_000_000,  # type: ignore[operator]
             "microsecond",
             expr_kind=self._compliant_expr._expr_kind,
         )
 
     def nanosecond(self: Self) -> DuckDBExpr:
         return self._compliant_expr._from_call(
             lambda _input: FunctionExpression("nanosecond", _input)
-            - FunctionExpression("second", _input) * 1_000_000_000,
+            - FunctionExpression("second", _input) * 1_000_000_000,  # type: ignore[operator]
             "nanosecond",
             expr_kind=self._compliant_expr._expr_kind,
         )
@@ -123,7 +123,7 @@ def total_minutes(self: Self) -> DuckDBExpr:
     def total_seconds(self: Self) -> DuckDBExpr:
         return self._compliant_expr._from_call(
             lambda _input: 60
-            * FunctionExpression("datepart", ConstantExpression("minute"), _input)
+            * FunctionExpression("datepart", ConstantExpression("minute"), _input)  # type: ignore[operator]
             + FunctionExpression("datepart", ConstantExpression("second"), _input),
             "total_seconds",
             expr_kind=self._compliant_expr._expr_kind,
@@ -132,7 +132,7 @@ def total_seconds(self: Self) -> DuckDBExpr:
     def total_milliseconds(self: Self) -> DuckDBExpr:
         return self._compliant_expr._from_call(
             lambda _input: 60_000
-            * FunctionExpression("datepart", ConstantExpression("minute"), _input)
+            * FunctionExpression("datepart", ConstantExpression("minute"), _input)  # type: ignore[operator]
             + FunctionExpression("datepart", ConstantExpression("millisecond"), _input),
             "total_milliseconds",
             expr_kind=self._compliant_expr._expr_kind,
@@ -141,7 +141,7 @@ def total_milliseconds(self: Self) -> DuckDBExpr:
     def total_microseconds(self: Self) -> DuckDBExpr:
         return self._compliant_expr._from_call(
             lambda _input: 60_000_000
-            * FunctionExpression("datepart", ConstantExpression("minute"), _input)
+            * FunctionExpression("datepart", ConstantExpression("minute"), _input)  # type: ignore[operator]
             + FunctionExpression("datepart", ConstantExpression("microsecond"), _input),
             "total_microseconds",
             expr_kind=self._compliant_expr._expr_kind,

narwhals/_duckdb/expr_str.py

@@ -54,10 +54,10 @@ def func(_input: duckdb.Expression) -> duckdb.Expression:
                 _input,
                 ConstantExpression(offset + 1)
                 if offset >= 0
-                else FunctionExpression("length", _input) + offset + 1,
+                else FunctionExpression("length", _input) + offset + 1,  # type: ignore[operator]
                 FunctionExpression("length", _input)
                 if length is None
-                else ConstantExpression(length) + offset,
+                else ConstantExpression(length) + offset,  # type: ignore[operator]
             )
 
         return self._compliant_expr._from_call(

narwhals/_duckdb/group_by.py

@@ -3,6 +3,7 @@
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
+    from duckdb import Expression
     from typing_extensions import Self
 
     from narwhals._duckdb.dataframe import DuckDBLazyFrame
@@ -23,7 +24,7 @@ def __init__(
         self._keys = keys
 
     def agg(self: Self, *exprs: DuckDBExpr) -> DuckDBLazyFrame:
-        agg_columns = self._keys.copy()
+        agg_columns: list[str | Expression] = list(self._keys)
         df = self._compliant_frame
         for expr in exprs:
             output_names = expr._evaluate_output_names(df)
@@ -49,5 +50,5 @@ def agg(self: Self, *exprs: DuckDBExpr) -> DuckDBLazyFrame:
             )
 
         return self._compliant_frame._from_native_frame(
-            self._compliant_frame._native_frame.aggregate(agg_columns)
+            self._compliant_frame._native_frame.aggregate(agg_columns)  # type: ignore[arg-type]
         )