Enable type hint checking (#5956)

* Enable type hint checking

* Add whatsnew entry

* Add class variable annotation

* Update line numbers in doctests

* Implement suggestions from code review

* Update docs/src/whatsnew/latest.rst

Co-authored-by: Martin Yeo <40734014+trexfeathers@users.noreply.github.com>

* Workaround for python/mypy#1465

Co-authored-by: Martin Yeo <40734014+trexfeathers@users.noreply.github.com>

* Also apply workaround for bounds

* Add type hint

---------

Co-authored-by: Martin Yeo <40734014+trexfeathers@users.noreply.github.com>

.pre-commit-config.yaml

@@ -62,6 +62,14 @@ repos:
     -   id: sort-all
         types: [file, python]
 
+-   repo: https://github.com/pre-commit/mirrors-mypy
+    rev: 'v1.9.0'
+    hooks:
+    -   id: mypy
+        additional_dependencies:
+            - 'types-requests'
+        exclude: 'noxfile\.py|docs/src/conf\.py'
+
 -   repo: https://github.com/numpy/numpydoc
     rev: v1.7.0
     hooks:

benchmarks/asv_delegated_conda.py

@@ -13,6 +13,7 @@
 from pathlib import Path
 from shutil import copy2, copytree, rmtree
 from tempfile import TemporaryDirectory
+from typing import Callable
 
 from asv import util as asv_util
 from asv.config import Config
@@ -99,6 +100,7 @@ def name(self):
     def _update_info(self) -> None:
         """Make sure class properties reflect the actual environment being used."""
         # Follow symlink if it has been created.
+        self._path: str
         actual_path = Path(self._path).resolve()
         self._path = str(actual_path)
 
@@ -132,7 +134,7 @@ def copy_asv_files(src_parent: Path, dst_parent: Path) -> None:
                     #  happened. Also a non-issue when copying in the reverse
                     #  direction because the cache dir is temporary.
                     if src_path.is_dir():
-                        func = copytree
+                        func: Callable = copytree
                     else:
                         func = copy2
                     func(src_path, dst_path)

benchmarks/benchmarks/cube.py

@@ -55,7 +55,7 @@ def time_create(self, _, cube_creation_strategy: str) -> None:
             new_cube.attributes = self.cube_kwargs["attributes"]
             new_cube.cell_methods = self.cube_kwargs["cell_methods"]
             for coord, dims in self.cube_kwargs["dim_coords_and_dims"]:
-                coord: coords.DimCoord  # Type hint to help linters.
+                assert isinstance(coord, coords.DimCoord)  # Type hint to help linters.
                 new_cube.add_dim_coord(coord, dims)
             for coord, dims in self.cube_kwargs["aux_coords_and_dims"]:
                 new_cube.add_aux_coord(coord, dims)

benchmarks/benchmarks/experimental/ugrid/regions_combine.py

@@ -210,7 +210,7 @@ def track_filesize_saved(self, n_cubesphere):
         return os.path.getsize("tmp.nc") * 1.0e-6
 
 
-CombineRegionsSaveData.track_filesize_saved.unit = "Mb"
+CombineRegionsSaveData.track_filesize_saved.unit = "Mb"  # type: ignore[attr-defined]
 
 
 class CombineRegionsFileStreamedCalc(MixinCombineRegions):

benchmarks/benchmarks/load/__init__.py

@@ -15,16 +15,16 @@
 class LoadAndRealise:
     # For data generation
     timeout = 600.0
-    params = [
+    params = (
         [(50, 50, 2), (1280, 960, 5), (2, 2, 1000)],
         [False, True],
         ["FF", "PP", "NetCDF"],
-    ]
+    )
     param_names = ["xyz", "compressed", "file_format"]
 
     def setup_cache(self) -> dict:
         file_type_args = self.params[2]
-        file_path_dict = {}
+        file_path_dict: dict[tuple[int, int, int], dict[bool, dict[str, str]]] = {}
         for xyz in self.params[0]:
             file_path_dict[xyz] = {}
             x, y, z = xyz
@@ -59,7 +59,7 @@ def time_realise(self, _, __, ___, ____) -> None:
 
 class STASHConstraint:
     # xyz sizes mimic LoadAndRealise to maximise file reuse.
-    params = [[(2, 2, 2), (1280, 960, 5), (2, 2, 1000)], ["FF", "PP"]]
+    params = ([(2, 2, 2), (1280, 960, 5), (2, 2, 1000)], ["FF", "PP"])
     param_names = ["xyz", "file_format"]
 
     def setup_cache(self) -> dict:
@@ -78,7 +78,7 @@ def time_stash_constraint(self, _, __, ___) -> None:
 
 
 class TimeConstraint:
-    params = [[3, 20], ["FF", "PP", "NetCDF"]]
+    params = ([3, 20], ["FF", "PP", "NetCDF"])
     param_names = ["time_dim_len", "file_format"]
 
     def setup_cache(self) -> dict:
@@ -139,7 +139,7 @@ class StructuredFF:
     avoiding the cost of merging.
     """
 
-    params = [[(2, 2, 2), (1280, 960, 5), (2, 2, 1000)], [False, True]]
+    params = ([(2, 2, 2), (1280, 960, 5), (2, 2, 1000)], [False, True])
     param_names = ["xyz", "structured_loading"]
 
     def setup_cache(self) -> dict:

benchmarks/bm_runner.py

@@ -136,7 +136,7 @@ def _setup_common() -> None:
 
 def _asv_compare(*commits: str, overnight_mode: bool = False) -> None:
     """Run through a list of commits comparing each one to the next."""
-    commits = [commit[:8] for commit in commits]
+    commits = tuple(commit[:8] for commit in commits)
     for i in range(len(commits) - 1):
         before = commits[i]
         after = commits[i + 1]
@@ -235,19 +235,19 @@ def _gh_create_reports(commit_sha: str, results_full: str, results_shifts: str)
 
             for login_type in ("author", "mergedBy"):
                 gh_query = f'.["{login_type}"]["login"]'
-                command = shlex.split(
+                commandlist = shlex.split(
                     f"gh pr view {pr_tag[1:]} "
                     f"--json {login_type} -q '{gh_query}' "
                     f"--repo {repo}"
                 )
-                login = _subprocess_runner_capture(command)
+                login = _subprocess_runner_capture(commandlist)
 
-                command = [
+                commandlist = [
                     "curl",
                     "-s",
                     f"https://api.github.com/users/{login}",
                 ]
-                login_info = _subprocess_runner_capture(command)
+                login_info = _subprocess_runner_capture(commandlist)
                 is_user = '"type": "User"' in login_info
                 if is_user:
                     assignee = login
@@ -313,7 +313,7 @@ class _SubParserGenerator(ABC):
     description: str = NotImplemented
     epilog: str = NotImplemented
 
-    def __init__(self, subparsers: ArgumentParser.add_subparsers) -> None:
+    def __init__(self, subparsers: argparse._SubParsersAction[ArgumentParser]) -> None:
         self.subparser: ArgumentParser = subparsers.add_parser(
             self.name,
             description=self.description,
@@ -476,10 +476,12 @@ def csperf(args: argparse.Namespace, run_type: Literal["cperf", "sperf"]) -> Non
         environ["ON_DEMAND_BENCHMARKS"] = "True"
         commit_range = "upstream/main^!"
 
-        asv_command = ASV_HARNESS.format(posargs=commit_range) + f" --bench={run_type}"
+        asv_command_str = (
+            ASV_HARNESS.format(posargs=commit_range) + f" --bench={run_type}"
+        )
 
         # Only do a single round.
-        asv_command = shlex.split(re.sub(r"rounds=\d", "rounds=1", asv_command))
+        asv_command = shlex.split(re.sub(r"rounds=\d", "rounds=1", asv_command_str))
         try:
             _subprocess_runner([*asv_command, *args.asv_args], asv=True)
         except subprocess.CalledProcessError as err:
@@ -584,7 +586,7 @@ def func(args: argparse.Namespace) -> None:
             environ["DATA_GEN_PYTHON"] = str(python_path)
         _setup_common()
         # get path of data-gen environment, setup by previous call
-        python_path = environ["DATA_GEN_PYTHON"]
+        python_path = Path(environ["DATA_GEN_PYTHON"])
         # allow 'on-demand' benchmarks
         environ["ON_DEMAND_BENCHMARKS"] = "1"
         asv_command = [

docs/src/further_topics/filtering_warnings.rst

@@ -47,9 +47,9 @@ Warnings:
 
     >>> my_operation()
     ...
-    iris/coord_systems.py:444: IrisUserWarning: Setting inverse_flattening does not affect other properties of the GeogCS object. To change other properties set them explicitly or create a new GeogCS instance.
+    iris/coord_systems.py:445: IrisUserWarning: Setting inverse_flattening does not affect other properties of the GeogCS object. To change other properties set them explicitly or create a new GeogCS instance.
       warnings.warn(wmsg, category=iris.warnings.IrisUserWarning)
-    iris/coord_systems.py:770: IrisDefaultingWarning: Discarding false_easting and false_northing that are not used by Cartopy.
+    iris/coord_systems.py:771: IrisDefaultingWarning: Discarding false_easting and false_northing that are not used by Cartopy.
       warnings.warn(
 
 Warnings can be suppressed using the Python warnings filter with the ``ignore``
@@ -110,7 +110,7 @@ You can target specific Warning messages, e.g.
     ...     warnings.filterwarnings("ignore", message="Discarding false_easting")
     ...     my_operation()
     ...
-    iris/coord_systems.py:444: IrisUserWarning: Setting inverse_flattening does not affect other properties of the GeogCS object. To change other properties set them explicitly or create a new GeogCS instance.
+    iris/coord_systems.py:445: IrisUserWarning: Setting inverse_flattening does not affect other properties of the GeogCS object. To change other properties set them explicitly or create a new GeogCS instance.
       warnings.warn(wmsg, category=iris.warnings.IrisUserWarning)
 
 ::
@@ -125,16 +125,16 @@ Or you can target Warnings raised by specific lines of specific modules, e.g.
 .. doctest:: filtering_warnings
 
     >>> with warnings.catch_warnings():
-    ...     warnings.filterwarnings("ignore", module="iris.coord_systems", lineno=444)
+    ...     warnings.filterwarnings("ignore", module="iris.coord_systems", lineno=445)
     ...     my_operation()
     ...
-    iris/coord_systems.py:770: IrisDefaultingWarning: Discarding false_easting and false_northing that are not used by Cartopy.
+    iris/coord_systems.py:771: IrisDefaultingWarning: Discarding false_easting and false_northing that are not used by Cartopy.
       warnings.warn(
 
 ::
 
-    python -W ignore:::iris.coord_systems:444
-    export PYTHONWARNINGS=ignore:::iris.coord_systems:444
+    python -W ignore:::iris.coord_systems:445
+    export PYTHONWARNINGS=ignore:::iris.coord_systems:445
 
 Warnings from a Common Source
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -188,7 +188,7 @@ module during execution:
     ...     )
     ...     my_operation()
     ...
-    iris/coord_systems.py:444: IrisUserWarning: Setting inverse_flattening does not affect other properties of the GeogCS object. To change other properties set them explicitly or create a new GeogCS instance.
+    iris/coord_systems.py:445: IrisUserWarning: Setting inverse_flattening does not affect other properties of the GeogCS object. To change other properties set them explicitly or create a new GeogCS instance.
       warnings.warn(wmsg, category=iris.warnings.IrisUserWarning)
 
 ----

docs/src/whatsnew/latest.rst

@@ -145,6 +145,9 @@ This document explains the changes made to Iris for this release
 
 #. `@rcomer`_ made some :meth:`~iris.cube.Cube.slices_over` tests go faster (:pull:`5973`)
 
+#. `@bouweandela`_ enabled mypy checks for type hints.
+   The entire team would like to thank Bouwe for putting in the hard
+   work on an unglamorous but highly valuable contribution. (:pull:`5956`)
 
 .. comment
     Whatsnew author names (@github name) in alphabetical order. Note that,

lib/iris/__init__.py

@@ -94,6 +94,7 @@ def callback(cube, field, filename):
 import itertools
 import os.path
 import threading
+from typing import Callable, Literal
 
 import iris._constraints
 import iris.config
@@ -189,7 +190,7 @@ def __repr__(self):
         return msg.format(self.datum_support, self.pandas_ndim, self.save_split_attrs)
 
     # deprecated_options = {'example_future_flag': 'warning',}
-    deprecated_options = {}
+    deprecated_options: dict[str, Literal["error", "warning"]] = {}
 
     def __setattr__(self, name, value):
         if name in self.deprecated_options:
@@ -248,7 +249,10 @@ def context(self, **kwargs):
 
 # Initialise the site configuration dictionary.
 #: Iris site configuration dictionary.
-site_configuration = {}
+site_configuration: dict[
+    Literal["cf_profile", "cf_patch", "cf_patch_conventions"],
+    Callable | Literal[False] | None,
+] = {}
 
 try:
     from iris.site_config import update as _update

lib/iris/_lazy_data.py

@@ -9,6 +9,7 @@
 """
 
 from functools import lru_cache, wraps
+from types import ModuleType
 from typing import Sequence
 
 import dask
@@ -376,7 +377,7 @@ def _combine(
     lazy = any(is_lazy_data(a) for a in arrays)
     masked = any(is_masked_data(a) for a in arrays)
 
-    array_module = np
+    array_module: ModuleType = np
     if masked:
         if lazy:
             # Avoid inconsistent array type when slicing resulting array

lib/iris/analysis/__init__.py

@@ -1848,7 +1848,7 @@ def interp_order(length):
 and lazy data.
 
 """
-MAX_RUN.name = lambda: "max_run"
+MAX_RUN.name = lambda: "max_run"  # type: ignore[method-assign]
 
 
 GMEAN = Aggregator("geometric_mean", scipy.stats.mstats.gmean)

lib/iris/analysis/maths.py

@@ -558,7 +558,7 @@ def exponentiate(cube, exponent, in_place=False):
     )
     if cube.has_lazy_data():
 
-        def power(data):
+        def power(data, out=None):
             return operator.pow(data, exponent)
 
     else:

lib/iris/common/metadata.py

@@ -141,7 +141,7 @@ class BaseMetadata(metaclass=_NamedTupleMeta):
 
     DEFAULT_NAME = "unknown"  # the fall-back name for metadata identity
 
-    _members = (
+    _members: str | Iterable[str] = (
         "standard_name",
         "long_name",
         "var_name",
@@ -870,7 +870,7 @@ def equal(self, other, lenient=None):
 class CoordMetadata(BaseMetadata):
     """Metadata container for a :class:`~iris.coords.Coord`."""
 
-    _members = ("coord_system", "climatological")
+    _members: str | Iterable[str] = ("coord_system", "climatological")
 
     __slots__ = ()
 

lib/iris/common/resolve.py

@@ -31,7 +31,7 @@
 
 
 _AuxCoverage = namedtuple(
-    "AuxCoverage",
+    "_AuxCoverage",
     [
         "cube",
         "common_items_aux",
@@ -45,18 +45,18 @@
 )
 
 _CategoryItems = namedtuple(
-    "CategoryItems",
+    "_CategoryItems",
     ["items_dim", "items_aux", "items_scalar"],
 )
 
 _DimCoverage = namedtuple(
-    "DimCoverage",
+    "_DimCoverage",
     ["cube", "metadata", "coords", "dims_common", "dims_local", "dims_free"],
 )
 
-_Item = namedtuple("Item", ["metadata", "coord", "dims"])
+_Item = namedtuple("_Item", ["metadata", "coord", "dims"])
 
-_PreparedFactory = namedtuple("PreparedFactory", ["container", "dependencies"])
+_PreparedFactory = namedtuple("_PreparedFactory", ["container", "dependencies"])
 
 
 @dataclass
@@ -95,7 +95,7 @@ def create_coord(self, metadata):
         return result
 
 
-_PreparedMetadata = namedtuple("PreparedMetadata", ["combined", "src", "tgt"])
+_PreparedMetadata = namedtuple("_PreparedMetadata", ["combined", "src", "tgt"])
 
 
 class Resolve:

lib/iris/coord_systems.py

@@ -7,6 +7,7 @@
 from abc import ABCMeta, abstractmethod
 from functools import cached_property
 import re
+from typing import ClassVar
 import warnings
 
 import cartopy.crs as ccrs
@@ -48,7 +49,7 @@ def _float_or_None(arg):
 class CoordSystem(metaclass=ABCMeta):
     """Abstract base class for coordinate systems."""
 
-    grid_mapping_name = None
+    grid_mapping_name: ClassVar[str | None] = None
 
     def __eq__(self, other):
         """Override equality.

lib/iris/coords.py

@@ -2704,7 +2704,12 @@ def _new_points_requirements(self, points):
             emsg = "The {!r} {} points array must be strictly monotonic."
             raise ValueError(emsg.format(self.name(), self.__class__.__name__))
 
-    @Coord._values.setter
+    @property
+    def _values(self):
+        # Overridden just to allow .setter override.
+        return super()._values
+
+    @_values.setter
     def _values(self, points):
         # DimCoord always realises the points, to allow monotonicity checks.
         # Ensure it is an actual array, and also make our own copy so that we
@@ -2796,7 +2801,12 @@ def _new_bounds_requirements(self, bounds):
 
         return bounds
 
-    @Coord.bounds.setter
+    @property
+    def bounds(self):
+        # Overridden just to allow .setter override.
+        return super().bounds
+
+    @bounds.setter
     def bounds(self, bounds):
         if bounds is not None:
             # Ensure we have a realised array of new bounds values.