Enable mypy in pre-commit

.pre-commit-config.yaml

@@ -28,3 +28,15 @@ repos:
     hooks:
       - id: nbstripout
         args: [--extra-keys=metadata.kernelspec metadata.language_info.version]
+-   repo: https://github.com/pre-commit/mirrors-mypy
+    rev: "v1.8.0"
+    hooks:
+      - id: mypy
+        verbose: true
+        args: ["--ignore-missing-imports", "--show-error-codes"]
+        additional_dependencies: [
+          "types-requests",
+          "pandas-stubs",
+          "pint",
+          "matplotlib-stubs",
+        ]

docs/conf.py

@@ -5,7 +5,7 @@
 # https://www.sphinx-doc.org/en/master/usage/configuration.html
 
 import datetime
-from importlib.metadata import version
+from importlib.metadata import version as metadata_version
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
@@ -22,7 +22,7 @@
 # built documents.
 
 try:  # pragma: no cover
-    version = version(project)
+    version = metadata_version(project)
 except Exception:  # pragma: no cover
     # we seem to have a local copy not installed without setuptools
     # so the reported version will be unknown

pint_pandas/__init__.py

@@ -6,7 +6,7 @@
     from importlib.metadata import version
 except ImportError:
     # Backport for Python < 3.8
-    from importlib_metadata import version
+    from importlib_metadata import version  # type: ignore
 
 try:  # pragma: no cover
     __version__ = version("pint_pandas")

pint_pandas/pint_array.py

@@ -2,7 +2,7 @@
 import re
 import warnings
 from importlib.metadata import version
-from typing import Optional
+from typing import Any, Callable, Dict, Optional, Union, cast
 
 import numpy as np
 import pandas as pd
@@ -11,15 +11,15 @@
 from pandas.api.extensions import (
     ExtensionArray,
     ExtensionDtype,
+    ExtensionScalarOpsMixin,
     register_dataframe_accessor,
     register_extension_dtype,
     register_series_accessor,
 )
+from pandas.api.indexers import check_array_indexer
 from pandas.api.types import is_integer, is_list_like, is_object_dtype, is_string_dtype
 from pandas.compat import set_function_name
-from pandas.core import nanops
-from pandas.core.arrays.base import ExtensionOpsMixin
-from pandas.core.indexers import check_array_indexer
+from pandas.core import nanops  # type: ignore
 from pint import Quantity as _Quantity
 from pint import Unit as _Unit
 from pint import compat, errors
@@ -47,7 +47,7 @@ class PintType(ExtensionDtype):
     units: Optional[_Unit] = None  # Filled in by `construct_from_..._string`
     _metadata = ("units",)
     _match = re.compile(r"(P|p)int\[(?P<units>.+)\]")
-    _cache = {}
+    _cache = {}  # type: ignore
     ureg = pint.get_application_registry()
 
     @property
@@ -78,11 +78,13 @@ def __new__(cls, units=None):
             units = cls.ureg.Quantity(1, units).units
 
         try:
-            return cls._cache["{:P}".format(units)]
+            # TODO: fix when Pint implements Callable typing
+            # TODO: wrap string into PintFormatStr class
+            return cls._cache["{:P}".format(units)]  # type: ignore
         except KeyError:
             u = object.__new__(cls)
             u.units = units
-            cls._cache["{:P}".format(units)] = u
+            cls._cache["{:P}".format(units)] = u  # type: ignore
             return u
 
     @classmethod
@@ -193,9 +195,9 @@ def __repr__(self):
 
 
 _NumpyEADtype = (
-    pd.core.dtypes.dtypes.PandasDtype
+    pd.core.dtypes.dtypes.PandasDtype  # type: ignore
     if pandas_version_info < (2, 1)
-    else pd.core.dtypes.dtypes.NumpyEADtype
+    else pd.core.dtypes.dtypes.NumpyEADtype  # type: ignore
 )
 
 dtypemap = {
@@ -215,7 +217,7 @@ def __repr__(self):
 dtypeunmap = {v: k for k, v in dtypemap.items()}
 
 
-class PintArray(ExtensionArray, ExtensionOpsMixin):
+class PintArray(ExtensionArray, ExtensionScalarOpsMixin):
     """Implements a class to describe an array of physical quantities:
     the product of an array of numerical values and a unit of measurement.
 
@@ -234,7 +236,7 @@ class PintArray(ExtensionArray, ExtensionOpsMixin):
 
     """
 
-    _data = np.array([])
+    _data: ExtensionArray = cast(ExtensionArray, np.array([]))
     context_name = None
     context_units = None
 
@@ -383,7 +385,7 @@ def isna(self):
         -------
         missing : np.array
         """
-        return self._data.isna()
+        return cast(np.ndarray, self._data.isna())
 
     def astype(self, dtype, copy=True):
         """Cast to a NumPy array with 'dtype'.
@@ -620,11 +622,11 @@ def unique(self):
         data = self._data
         return self._from_sequence(unique(data), dtype=self.dtype)
 
-    def __contains__(self, item) -> bool:
+    def __contains__(self, item) -> Union[bool, np.bool_]:
         if not isinstance(item, _Quantity):
             return False
         elif pd.isna(item.magnitude):
-            return self.isna().any()
+            return cast(np.ndarray, self.isna()).any()
         else:
             return super().__contains__(item)
 
@@ -908,11 +910,12 @@ def _reduce(self, name, *, skipna: bool = True, keepdims: bool = False, **kwds):
 
         if isinstance(self._data, ExtensionArray):
             try:
-                result = self._data._reduce(
+                # TODO: https://github.com/pandas-dev/pandas-stubs/issues/850
+                result = self._data._reduce(  # type: ignore
                     name, skipna=skipna, keepdims=keepdims, **kwds
                 )
             except NotImplementedError:
-                result = functions[name](self.numpy_data, **kwds)
+                result = cast(_Quantity, functions[name](self.numpy_data, **kwds))
 
         if name in {"all", "any", "kurt", "skew"}:
             return result
@@ -927,15 +930,18 @@ def _reduce(self, name, *, skipna: bool = True, keepdims: bool = False, **kwds):
     def _accumulate(self, name: str, *, skipna: bool = True, **kwds):
         if name == "cumprod":
             raise TypeError("cumprod not supported for pint arrays")
-        functions = {
+        functions: Dict[
+            str, Callable[[np._typing._SupportsArray[np.dtype[Any]]], Any]
+        ] = {
             "cummin": np.minimum.accumulate,
             "cummax": np.maximum.accumulate,
             "cumsum": np.cumsum,
         }
 
         if isinstance(self._data, ExtensionArray):
             try:
-                result = self._data._accumulate(name, **kwds)
+                # TODO: https://github.com/pandas-dev/pandas-stubs/issues/850
+                result = self._data._accumulate(name, **kwds)  # type: ignore
             except NotImplementedError:
                 result = functions[name](self.numpy_data, **kwds)
 
@@ -1181,9 +1187,10 @@ def is_pint_type(obj):
 
 try:
     # for pint < 0.21 we need to explicitly register
-    compat.upcast_types.append(PintArray)
+    # TODO: fix when Pint is properly typed for mypy
+    compat.upcast_types.append(PintArray)  # type: ignore
 except AttributeError:
     # for pint = 0.21 we need to add the full names of PintArray and DataFrame,
     # which is to be added in pint > 0.21
-    compat.upcast_type_map.setdefault("pint_pandas.pint_array.PintArray", PintArray)
-    compat.upcast_type_map.setdefault("pandas.core.frame.DataFrame", DataFrame)
+    compat.upcast_type_map.setdefault("pint_pandas.pint_array.PintArray", PintArray)  # type: ignore
+    compat.upcast_type_map.setdefault("pandas.core.frame.DataFrame", DataFrame)  # type: ignore

pint_pandas/testsuite/test_pandas_extensiontests.py

@@ -18,7 +18,6 @@
     use_numpy,  # noqa: F401
 )
 
-
 from pint.errors import DimensionalityError
 
 from pint_pandas import PintArray, PintType
@@ -381,9 +380,10 @@ def _get_expected_exception(
                 return TypeError
             if isinstance(obj, pd.Series):
                 try:
-                    if obj.pint.m.dtype.kind == "c":
+                    # PintSeriesAccessor is dynamically constructed; need stubs to make it mypy-compatible
+                    if obj.pint.m.dtype.kind == "c":  # type: ignore
                         pytest.skip(
-                            f"{obj.pint.m.dtype.name} {obj.dtype} does not support {op_name}"
+                            f"{obj.pint.m.dtype.name} {obj.dtype} does not support {op_name}"  # type: ignore
                         )
                         return TypeError
                 except AttributeError:
@@ -392,9 +392,9 @@ def _get_expected_exception(
                         return exc
             if isinstance(other, pd.Series):
                 try:
-                    if other.pint.m.dtype.kind == "c":
+                    if other.pint.m.dtype.kind == "c":  # type: ignore
                         pytest.skip(
-                            f"{other.pint.m.dtype.name} {other.dtype} does not support {op_name}"
+                            f"{other.pint.m.dtype.name} {other.dtype} does not support {op_name}"  # type: ignore
                         )
                         return TypeError
                 except AttributeError: