RF: Cache supported_np_types by class

Author: effigies

nibabel/spatialimages.py

@@ -143,6 +143,11 @@
 from .viewers import OrthoSlicer3D
 from .volumeutils import shape_zoom_affine
 
+try:
+    from functools import cache
+except ImportError:  # PY38
+    from functools import lru_cache as cache
+
 
 class HeaderDataError(Exception):
     """Class to indicate error in getting or setting header data"""
@@ -268,22 +273,29 @@ def data_from_fileobj(self, fileobj):
         return np.ndarray(shape, dtype, data_bytes, order=self.data_layout)
 
 
-def supported_np_types(obj):
-    """Numpy data types that instance `obj` supports
+@cache
+def _supported_np_types(klass):
+    """Numpy data types that instances of ``klass`` support
 
     Parameters
     ----------
-    obj : object
-        Object implementing `get_data_dtype` and `set_data_dtype`.  The object
+    klass : class
+        Class implementing `get_data_dtype` and `set_data_dtype` methods.  The object
         should raise ``HeaderDataError`` for setting unsupported dtypes. The
         object will likely be a header or a :class:`SpatialImage`
 
     Returns
     -------
     np_types : set
-        set of numpy types that `obj` supports
+        set of numpy types that ``klass`` instances support
     """
-    dt = obj.get_data_dtype()
+    try:
+        obj = klass()
+    except TypeError as e:
+        if hasattr(klass, 'header_class'):
+            obj = klass.header_class()
+        else:
+            raise e
     supported = set()
     for np_type in set(np.sctypeDict.values()):
         try:
@@ -293,10 +305,27 @@ def supported_np_types(obj):
         # Did set work?
         if np.dtype(obj.get_data_dtype()) == np.dtype(np_type):
             supported.add(np_type)
-    obj.set_data_dtype(dt)
     return supported
 
 
+def supported_np_types(obj):
+    """Numpy data types that instance `obj` supports
+
+    Parameters
+    ----------
+    obj : object
+        Object implementing `get_data_dtype` and `set_data_dtype`.  The object
+        should raise ``HeaderDataError`` for setting unsupported dtypes. The
+        object will likely be a header or a :class:`SpatialImage`
+
+    Returns
+    -------
+    np_types : set
+        set of numpy types that `obj` supports
+    """
+    return _supported_np_types(obj.__class__)
+
+
 class ImageDataError(Exception):
     pass