ENH: add np.issubdtype checker to mimic numpy

Author: ev-br

Diff for: torch_np/_dtypes.py

@@ -10,6 +10,10 @@
 
 from . import _scalar_types
 
+
+__all__ = ['dtype_from_torch', 'dtype', 'typecodes', 'issubdtype']
+
+
 # Define analogs of numpy dtypes supported by pytorch.
 
 class dtype:
@@ -177,6 +181,23 @@ def is_integer(dtyp):
     return dtyp.typecode in typecodes['AllInteger']
 
 
+
+def issubclass_(arg, klass):
+    try:
+        return issubclass(arg, klass)
+    except TypeError:
+        return False
+
+
+def issubdtype(arg1, arg2):
+    # cf https://github.com/numpy/numpy/blob/v1.24.0/numpy/core/numerictypes.py#L356-L420
+    if not issubclass_(arg1, _scalar_types.generic):
+        arg1 = dtype(arg1).type
+    if not issubclass_(arg2, _scalar_types.generic):
+        arg2 = dtype(arg2).type
+    return issubclass(arg1, arg2)
+
+
 # The casting below is defined *with dtypes only*, so no value-based casting!
 
 # These two dicts are autogenerated with autogen/gen_dtypes.py,
@@ -210,6 +231,3 @@ def is_integer(dtyp):
 
 ########################## end autogenerated part
 
-
-__all__ = ['dtype_from_torch', 'dtype', 'typecodes']
-