Move fix to infer dtype

Author: znicholls

xarray/coding/strings.py

@@ -17,6 +17,8 @@
 
 
 def create_vlen_dtype(element_type):
+    if element_type not in (str, bytes):
+        raise TypeError("Unsupported type for vlen_dtype: `{}`".format(element_type))
     # based on h5py.special_dtype
     return np.dtype("O", metadata={"element_type": element_type})
 
@@ -29,11 +31,7 @@ def check_vlen_dtype(dtype):
 
 
 def is_unicode_dtype(dtype):
-    return (
-        dtype.kind == "U"
-        or check_vlen_dtype(dtype) == str
-        or check_vlen_dtype(dtype) == np.str_
-    )
+    return dtype.kind == "U" or check_vlen_dtype(dtype) == str
 
 
 def is_bytes_dtype(dtype):

xarray/conventions.py

@@ -157,8 +157,10 @@ def _infer_dtype(array, name=None):
         return np.dtype(float)
 
     element = array[(0,) * array.ndim]
-    if isinstance(element, (bytes, str)):
+    if isinstance(element, bytes):
         return strings.create_vlen_dtype(type(element))
+    elif isinstance(element, str):
+        return strings.create_vlen_dtype(str)
 
     dtype = np.array(element).dtype
     if dtype.kind != "O":