fix inconsistent error handling for Grid.load()

- gOpenMol parser now captures its TypeError and raises ValueError if the
  header cannot be read; this makes it consistent with the other parsers
- removed XFAILs from tests that check failure behavior for incorrectly
  specified file_format for Grid/Grid.load()
- update CHANGELOG
- update docs for Grid.load()

Author: orbeckst

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/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 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

@@ -179,12 +179,9 @@ def test_load_fileformat(self, data, pklfile, fileformat):
         h = Grid(pklfile, file_format="pkl")
         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'):
+        with pytest.raises(ValueError):
             Grid(pklfile, file_format=fileformat)
 
     # just check that we can export without stupid failures; detailed