ENH: add isinf, isnan, fmin, fmax loops for datetime64, timedelta64 (#14841)

`np.datetime('NaT')` should behave more like `float('Nan')`. 
Add needed infrastructure so `np.isinf(a)` and `np.isnan(a)`
will run on `datetime64` and `timedelta64` dtypes.
Also added specific loops for `numpy.fmin` and `numpy.fmax`
that mask `NaT`.

1 files changed, 27 insertions, 15 deletions

diff --git a/numpy/testing/_private/utils.py b/numpy/testing/_private/utils.py
index 4eb168d18..b14c776d9 100644
--- a/numpy/testing/_private/utils.py
+++ b/numpy/testing/_private/utils.py
@@ -378,21 +378,6 @@ def assert_equal(actual, desired, err_msg='', verbose=True):
     if isscalar(desired) != isscalar(actual):
         raise AssertionError(msg)
 
-    # Inf/nan/negative zero handling
-    try:
-        isdesnan = gisnan(desired)
-        isactnan = gisnan(actual)
-        if isdesnan and isactnan:
-            return  # both nan, so equal
-
-        # handle signed zero specially for floats
-        if desired == 0 and actual == 0:
-            if not signbit(desired) == signbit(actual):
-                raise AssertionError(msg)
-
-    except (TypeError, ValueError, NotImplementedError):
-        pass
-
     try:
         isdesnat = isnat(desired)
         isactnat = isnat(actual)
@@ -408,6 +393,33 @@ def assert_equal(actual, desired, err_msg='', verbose=True):
     except (TypeError, ValueError, NotImplementedError):
         pass
 
+    # Inf/nan/negative zero handling
+    try:
+        isdesnan = gisnan(desired)
+        isactnan = gisnan(actual)
+        if isdesnan and isactnan:
+            return  # both nan, so equal
+
+        # handle signed zero specially for floats
+        array_actual = array(actual)
+        array_desired = array(desired)
+        if (array_actual.dtype.char in 'Mm' or
+                array_desired.dtype.char in 'Mm'):
+            # version 1.18
+            # until this version, gisnan failed for datetime64 and timedelta64.
+            # Now it succeeds but comparison to scalar with a different type
+            # emits a DeprecationWarning.
+            # Avoid that by skipping the next check
+            raise NotImplementedError('cannot compare to a scalar '
+                                      'with a different type')
+
+        if desired == 0 and actual == 0:
+            if not signbit(desired) == signbit(actual):
+                raise AssertionError(msg)
+
+    except (TypeError, ValueError, NotImplementedError):
+        pass
+
     try:
         # Explicitly use __eq__ for comparison, gh-2552
         if not (desired == actual):