fix inconsistent error handling for Grid.load()

CHANGELOG

@@ -15,9 +15,12 @@ The rules for this file:
 -------------------------------------------------------------------------------
 ??/??/???? orbeckst
 
- * 1.1.1
+ * 1.2.0
 
- Fixes
+  Fixes
+
+  * Ensure that when Grid() or Grid.load() load a datafile with the
+    wrong format a ValueError is raised consistently. (PR #165)
 
 
 01/22/2026 IAlibay, ollyfutur, conradolandia, orbeckst, PlethoraChutney,

gridData/OpenDX.py

@@ -561,10 +561,33 @@ def read(self, stream):
             dx = OpenDX.field.read(dxfile)
 
         The classid is discarded and replaced with the one from the file.
+
+        Parameters
+        ----------
+        stream : str or stream
+            read from the file in OpenDX format or open file-like object
+
+        Raises
+        ------
+        ValueError
+            if the data could not be parsed correctly
+
+
+        .. versionchanged:: 1.2.0
+           Ensure that ValueError is raised (instead of
+           :exc:`UnicodeDecodeError` or :exc:`RecursionError`)
+
         """
         DXfield = self
         p = DXParser(stream)
-        p.parse(DXfield)
+        try:
+            p.parse(DXfield)
+        except (UnicodeDecodeError, RecursionError) as err:
+            # parser got confused, likely not a valid file
+            # (RecursionError was only observed on Windows)
+            raise ValueError("DX file could not be read. "
+                             "The original error was\n"
+                             f"   {err.__class__.__name__}: {err}")
 
     def add(self,component,DXobj):
         """add a component to the field"""

gridData/core.py

@@ -558,6 +558,29 @@ def load(self, filename, file_format=None, assume_volumetric=False):
 
         The :meth:`load` method calls the class's constructor method and
         completely resets all values, based on the loaded data.
+
+        Parameters
+        ----------
+        filename : str
+             Name of the file.
+
+        file_format : str or None, optional
+             Set the file format (e.g., "DX" or "MRC"). If ``None`` then
+             try to guess the format.
+
+        assume_volumetric : bool, optional
+              Optional keyword argument that is only taken into account by
+              the :class:`gridData.mrc.MRC` file parser.
+
+        Raises
+        ------
+        ValueError
+             The underlying file parser raises an :exc:`ValueError` if it fails
+             to parse the file.
+
+
+        .. versionchanged:: 1.2.0
+           Ensure that underlying parsers consistently raise ValueError.
         """
         filename = str(filename)
         if not os.path.exists(filename):

gridData/gOpenMol.py

@@ -209,12 +209,17 @@ def read(self, filename):
         from struct import calcsize, unpack
         if not filename is None:
             self.filename = str(filename)
-        with open(self.filename, 'rb') as plt:
-            h = self.header = self._read_header(plt)
-            nentries = h['nx'] * h['ny'] * h['nz']
-            # quick and dirty... slurp it all in one go
-            datafmt = h['bsaflag']+str(nentries)+self._data_bintype
-            a = numpy.array(unpack(datafmt, plt.read(calcsize(datafmt))))
+        try:
+            with open(self.filename, 'rb') as plt:
+                h = self.header = self._read_header(plt)
+                nentries = h['nx'] * h['ny'] * h['nz']
+                # quick and dirty... slurp it all in one go
+                datafmt = h['bsaflag'] + str(nentries) + self._data_bintype
+                a = numpy.array(unpack(datafmt, plt.read(calcsize(datafmt))))
+        except Exception as err:
+            raise ValueError(f"gOpenMol PLT file {filename} could not be read. "
+                             "The original error was\n"
+                             f"   {err.__class__.__name__}: {err}")
         self.header['filename'] = self.filename
         self.array = a.reshape(h['nz'], h['ny'], h['nx']).transpose()  # unpack plt in reverse!!
         self.delta = self._delta()

gridData/tests/test_grid.py

@@ -176,15 +176,12 @@ def test_init_pickle_pathobjects(self, data, tmpdir):
 
     @pytest.mark.parametrize("fileformat", ("pkl", "PKL", "pickle", "python"))
     def test_load_fileformat(self, data, pklfile, fileformat):
-        h = Grid(pklfile, file_format="pkl")
+        h = Grid(pklfile, file_format=fileformat)
         assert h == data['grid']
 
-    # At the moment, reading the file with the wrong parser does not give
-    # good error messages.
-    @pytest.mark.xfail
     @pytest.mark.parametrize("fileformat", ("ccp4", "plt", "dx"))
-    def test_load_wrong_fileformat(self, data, pklfile, fileformat):
-        with pytest.raises('ValueError'):
+    def test_load_wrong_fileformat_raises_ValueError(self, pklfile, fileformat):
+        with pytest.raises(ValueError):
             Grid(pklfile, file_format=fileformat)
 
     # just check that we can export without stupid failures; detailed