Merge pull request matplotlib#24630 from ShawnZhong/main

Improve error message for gridspec when the index is not an integer.

Author: tacaswell

lib/matplotlib/gridspec.py

@@ -601,7 +601,9 @@ def _from_subplot_args(figure, args):
         else:
             if not isinstance(num, Integral) or num < 1 or num > rows*cols:
                 raise ValueError(
-                    f"num must be 1 <= num <= {rows*cols}, not {num!r}")
+                    f"num must be an integer with 1 <= num <= {rows*cols}, "
+                    f"not {num!r}"
+                )
             i = j = num
         return gs[i-1:j]
 

lib/matplotlib/tests/test_figure.py

@@ -236,10 +236,15 @@ def test_add_subplot_invalid():
     with pytest.raises(ValueError,
                        match='Number of rows must be a positive integer'):
         fig.add_subplot(0, 2, 1)
-    with pytest.raises(ValueError, match='num must be 1 <= num <= 4'):
+    with pytest.raises(ValueError, match='num must be an integer with '
+                                         '1 <= num <= 4'):
         fig.add_subplot(2, 2, 0)
-    with pytest.raises(ValueError, match='num must be 1 <= num <= 4'):
+    with pytest.raises(ValueError, match='num must be an integer with '
+                                         '1 <= num <= 4'):
         fig.add_subplot(2, 2, 5)
+    with pytest.raises(ValueError, match='num must be an integer with '
+                                         '1 <= num <= 4'):
+        fig.add_subplot(2, 2, 0.5)
 
     with pytest.raises(ValueError, match='must be a three-digit integer'):
         fig.add_subplot(42)