mfgrdfile: export follow-on

autotest/test_binarygrid_util.py

@@ -629,3 +629,55 @@ def test_write_grb_disu_v1_upgrade_to_v2(tmp_path, mfgrd_test_path):
     np.testing.assert_array_equal(grb_new.ja, grb_orig.ja)
     np.testing.assert_allclose(grb_new.top, grb_orig.top)
     np.testing.assert_allclose(grb_new.bot, grb_orig.bot)
+
+
+def test_write_grb_export_is_keyword_only(tmp_path, mfgrd_test_path):
+    """A positional call beyond filename raises."""
+    grb = MfGrdFile(mfgrd_test_path / "nwtp3.dis.grb", verbose=False)
+    with pytest.raises(TypeError):
+        grb.export(tmp_path / "out.grb", "double", 1, "EPSG:26916", True)
+
+
+def test_write_grb_empty_crs_argument_falls_back(tmp_path, mfgrd_test_path):
+    """An explicit empty/blank crs argument is treated like crs=None: it
+    falls back to the source file's CRS instead of overriding it."""
+    grb = MfGrdFile(mfgrd_test_path / "flow_v2.dis.grb", verbose=False)
+    assert grb.crs is not None
+
+    output_file = tmp_path / "out.grb"
+    grb.export(output_file, crs="")
+    grb_new = MfGrdFile(output_file, verbose=False)
+    assert grb_new.crs == grb.crs
+
+    output_file2 = tmp_path / "out2.grb"
+    grb.export(output_file2, crs="   ")
+    grb_new2 = MfGrdFile(output_file2, verbose=False)
+    assert grb_new2.crs == grb.crs
+
+
+def test_write_grb_empty_crs_argument_no_source_crs(tmp_path, mfgrd_test_path):
+    """An explicit empty/blank crs argument with no source CRS to fall
+    back on results in a version 1 file with no CRS, same as crs=None."""
+    grb = MfGrdFile(mfgrd_test_path / "nwtp3.dis.grb", verbose=False)
+    assert grb.crs is None
+
+    output_file = tmp_path / "out.grb"
+    grb.export(output_file, crs="")
+    grb_new = MfGrdFile(output_file, verbose=False)
+    assert grb_new.version == 1
+    assert grb_new.crs is None
+
+
+def test_write_grb_blank_source_crs_treated_as_absent(tmp_path, mfgrd_test_path):
+    """A source file's blank CRS is treated as absent on re-export:
+    version drops to 1 and no CRS field is written."""
+    grb = MfGrdFile(mfgrd_test_path / "flow_v2.dis.grb", verbose=False)
+    grb._datadict["CRS"] = ""
+
+    output_file = tmp_path / "blank_crs.grb"
+    grb.export(output_file)
+
+    grb_new = MfGrdFile(output_file, verbose=False)
+    assert grb_new.version == 1
+    assert grb_new.crs is None
+    assert "CRS" not in grb_new._datadict

flopy/mf6/utils/binarygrid_util.py

@@ -795,7 +795,15 @@ def cell2d(self):
             vertices, cell2d = None, None
         return vertices, cell2d
 
-    def export(self, filename, precision=None, version=None, crs=None, verbose=False):
+    def export(
+        self,
+        filename,
+        *,
+        precision=None,
+        version=None,
+        crs=None,
+        verbose=False,
+    ):
         """
         Export the binary grid file to a new file.
 
@@ -818,6 +826,11 @@ def export(self, filename, precision=None, version=None, crs=None, verbose=False
         verbose : bool, optional
             Print progress messages (default False)
 
+        All parameters except ``filename`` are keyword-only, so adding a
+        new parameter here in the future (e.g. a dedicated parameter and
+        property for a new GRB field, mirroring ``crs``/``.crs``) can
+        never silently change the meaning of an existing positional call.
+
         Examples
         --------
         >>> from flopy.mf6.utils import MfGrdFile
@@ -832,10 +845,17 @@ def export(self, filename, precision=None, version=None, crs=None, verbose=False
         if precision is None:
             precision = self.precision
 
+        if isinstance(crs, str) and crs.strip() == "":
+            crs = None
+
         raw_crs = crs if crs is not None else self.crs
         effective_crs = _crs_to_string(raw_crs) if raw_crs is not None else None
+        if effective_crs is not None and effective_crs.strip() == "":
+            # A blank CRS carries no usable information. Treat it the
+            # same as no CRS rather than writing an empty crs string.
+            effective_crs = None
         if version is None:
-            version = 2 if effective_crs else 1
+            version = 2 if effective_crs is not None else 1
 
         float_type = "SINGLE" if precision.lower() == "single" else "DOUBLE"
 
@@ -864,7 +884,7 @@ def export(self, filename, precision=None, version=None, crs=None, verbose=False
             data_dict[key] = self._datadict[key]
 
         if version >= 2:
-            if not effective_crs:
+            if effective_crs is None:
                 raise ValueError(
                     "version=2 requires a CRS string. Provide crs= or use a "
                     "version 2 source file."