DEP: deprecate np.finfo(None) (#23011)

dshintani404 · web-flow · commit 0cfbd3c4646a · 2023-01-19T18:20:49.000+01:00
Deprecate np.finfo(None), it may be that we should more generally deprecate `np.dtype(None)` but this is a start and particularly weird maybe. Closes gh-14684
diff --git a/doc/release/upcoming_changes/23011.deprecation.rst b/doc/release/upcoming_changes/23011.deprecation.rst
@@ -0,0 +1 @@
+* ``np.finfo(None)`` is deprecated.
diff --git a/numpy/core/getlimits.py b/numpy/core/getlimits.py
@@ -471,6 +471,15 @@ class finfo:
     _finfo_cache = {}
 
     def __new__(cls, dtype):
+        if dtype is None:
+            # Deprecated in NumPy 1.25, 2023-01-16
+            warnings.warn(
+                "finfo() dtype cannot be None. This behavior will "
+                "raise an error in the future. (Deprecated in NumPy 1.25)",
+                DeprecationWarning,
+                stacklevel=2
+            )
+
         try:
             dtype = numeric.dtype(dtype)
         except TypeError:
diff --git a/numpy/core/tests/test_deprecations.py b/numpy/core/tests/test_deprecations.py
@@ -1107,3 +1107,9 @@ def test_attributeerror_includes_info(self, name):
         msg = f".*\n`np.{name}` was a deprecated alias for the builtin"
         with pytest.raises(AttributeError, match=msg):
             getattr(np, name)
+
+
+class TestDeprecatedFinfo(_DeprecationTestCase):
+    # Deprecated in NumPy 1.25, 2023-01-16
+    def test_deprecated_none(self):
+        self.assert_deprecated(np.finfo, args=(None,))
