TYP: add a few type annotations to `numpy.array_api.Array`

This fixes the majority of the complaints for `$ mypy numpy/array_api`.
The comment indicating that one fix is blocked by lack of support in
Mypy for `NotImplemented` is responsible for another several dozen
errors.

[skip ci]

1 files changed, 5 insertions, 1 deletions

diff --git a/numpy/array_api/_array_object.py b/numpy/array_api/_array_object.py
index 75baf34b0..900a0ae1e 100644
--- a/numpy/array_api/_array_object.py
+++ b/numpy/array_api/_array_object.py
@@ -55,6 +55,7 @@ class Array:
     functions, such as asarray().
 
     """
+    _array: np.ndarray
 
     # Use a custom constructor instead of __init__, as manually initializing
     # this class is not supported API.
@@ -124,6 +125,9 @@ class Array:
     # spec in places where it either deviates from or is more strict than
     # NumPy behavior
 
+    # NOTE: no valid type annotation possible.  E.g `Union[Array,
+    # NotImplemented]` is forbidden, see https://github.com/python/mypy/issues/363
+    # Maybe change returned object to `Literal['NotImplemented']`?
     def _check_allowed_dtypes(self, other, dtype_category, op):
         """
         Helper function for operators to only allow specific input dtypes
@@ -200,7 +204,7 @@ class Array:
         return Array._new(np.array(scalar, self.dtype))
 
     @staticmethod
-    def _normalize_two_args(x1, x2):
+    def _normalize_two_args(x1, x2) -> Tuple[Array, Array]:
         """
         Normalize inputs to two arg functions to fix type promotion rules