Remove special case in guess_engines (#4777)

* Remove special case in guess_engines

* Sync the error messages between APIv1 and APIv2

xarray/backends/plugins.py

@@ -104,11 +104,6 @@ def list_engines():
 def guess_engine(store_spec):
     engines = list_engines()
 
-    # use the pre-defined selection order for netCDF files
-    for engine in ["netcdf4", "h5netcdf", "scipy"]:
-        if engine in engines and engines[engine].guess_can_open(store_spec):
-            return engine
-
     for engine, backend in engines.items():
         try:
             if backend.guess_can_open and backend.guess_can_open(store_spec):

xarray/core/utils.py

@@ -636,6 +636,7 @@ def read_magic_number(filename_or_obj, count=8):
     elif isinstance(filename_or_obj, io.IOBase):
         if filename_or_obj.tell() != 0:
             raise ValueError(
+                "cannot guess the engine, "
                 "file-like object read/write pointer not at the start of the file, "
                 "please close and reopen, or use a context manager"
             )

xarray/tests/test_backends.py

@@ -2661,7 +2661,7 @@ def test_open_fileobj(self):
                     open_dataset(f, engine="scipy")
 
                 f.seek(8)
-                with raises_regex(ValueError, "read/write pointer not at the start"):
+                with raises_regex(ValueError, "cannot guess the engine"):
                     open_dataset(f)