Allow only str or None inputs to outgrid parameter

Xref #1807

Author: weiji14

pygmt/src/triangulate.py

@@ -205,7 +205,7 @@ def regular_grid(  # pylint: disable=too-many-arguments,too-many-locals
         {J}
         {R}
         {I}
-        outgrid : str or bool or None
+        outgrid : str or None
             The name of the output netCDF file with extension .nc to store the
             grid in. The interpolation is performed in the original
             coordinates, so if your triangles are close to the poles you are
@@ -228,17 +228,22 @@ def regular_grid(  # pylint: disable=too-many-arguments,too-many-locals
         ret: xarray.DataArray or None
             Return type depends on whether the ``outgrid`` parameter is set:
 
-            - xarray.DataArray if ``outgrid`` is True or None (default)
+            - xarray.DataArray if ``outgrid`` is None (default)
             - None if ``outgrid`` is a str (grid output is stored in
               ``outgrid``)
         """
         # Return an xarray.DataArray if ``outgrid`` is not set
         with GMTTempFile(suffix=".nc") as tmpfile:
             if isinstance(outgrid, str):
                 output_type = "file"
-            else:
+            elif outgrid is None:
                 output_type = "xarray"
                 outgrid = tmpfile.name
+            else:
+                raise GMTInvalidInput(
+                    "'outgrid' should be a proper file name or `None`"
+                )
+
             return triangulate._triangulate(
                 data=data,
                 x=x,

pygmt/tests/test_triangulate.py

@@ -131,15 +131,13 @@ def test_delaunay_triples_invalid_format(dataframe):
         triangulate.delaunay_triples(data=dataframe, output_type="pandas", header="o+c")
 
 
-def test_regular_grid_with_outgrid_true(dataframe, expected_grid):
+def test_regular_grid_no_outgrid(dataframe, expected_grid):
     """
-    Run triangulate.regular_grid with outgrid=True and see it load into an
+    Run triangulate.regular_grid with no set outgrid and see it load into an
     xarray.DataArray.
     """
     data = dataframe.to_numpy()
-    output = triangulate.regular_grid(
-        data=data, spacing=1, region=[2, 4, 5, 6], outgrid=True
-    )
+    output = triangulate.regular_grid(data=data, spacing=1, region=[2, 4, 5, 6])
     assert isinstance(output, xr.DataArray)
     assert output.gmt.registration == 0  # Gridline registration
     assert output.gmt.gtype == 0  # Cartesian type
@@ -162,3 +160,12 @@ def test_regular_grid_with_outgrid_param(dataframe, expected_grid):
             assert grid.gmt.registration == 0  # Gridline registration
             assert grid.gmt.gtype == 0  # Cartesian type
             xr.testing.assert_allclose(a=grid, b=expected_grid)
+
+
+def test_regular_grid_invalid_format(dataframe):
+    """
+    Test that triangulate.regular_grid fails with outgrid that is not None or
+    a proper file name.
+    """
+    with pytest.raises(GMTInvalidInput):
+        triangulate.regular_grid(data=dataframe, outgrid=True)