RF: Add a more resilient method for fetching data dtype

Author: effigies

nibabel/arrayproxy.py

@@ -412,3 +412,17 @@ def reshape_dataobj(obj, shape):
     """
     return (obj.reshape(shape) if hasattr(obj, 'reshape')
             else np.reshape(obj, shape))
+
+
+def get_obj_dtype(obj):
+    """ Get the effective dtype of an array-like object """
+    if is_proxy(obj):
+        # Read and potentially apply scaling to one value
+        idx = (0,) * len(obj.shape)
+        return obj[idx].dtype
+    elif hasattr(obj, "dtype"):
+        # Trust the dtype (probably an ndarray)
+        return obj.dtype
+    else:
+        # Coerce; this could be expensive but we don't know what we can do with it
+        return np.asanyarray(obj).dtype

nibabel/nifti1.py

@@ -17,6 +17,7 @@
 import numpy.linalg as npl
 from numpy.compat.py3k import asstr
 
+from .arrayproxy import get_obj_dtype
 from .optpkg import optional_package
 from .filebasedimages import SerializableImage
 from .volumeutils import Recoder, make_dt_codes, endian_codes
@@ -1808,7 +1809,7 @@ def __init__(self, dataobj, affine, header=None,
         # not support 64-bit integer data, so `set_data_dtype(int64)` would
         # already fail.
         danger_dts = (np.dtype("int64"), np.dtype("uint64"))
-        if header is None and dtype is None and dataobj.dtype in danger_dts:
+        if header is None and dtype is None and get_obj_dtype(dataobj) in danger_dts:
             msg = (f"Image data has type {dataobj.dtype}, which may cause "
                    "incompatibilities with other tools. This will error in "
                    "NiBabel 5.0. This warning can be silenced "