Deprecate passing non-int to Table.auto_set_column_width

When iterables were added in matplotlib#6047, the test added a string. Typing
correctly points out that that is not accepted, and in fact it does not
do anything (as shown in the test image) because column keys are ints,
not strings.

doc/api/next_api_changes/deprecations/26444-ES.rst

@@ -0,0 +1,5 @@
+Passing non-int or sequence of non-int to ``Table.auto_set_column_width``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Column numbers are ints, and formerly passing any other type was effectively
+ignored. This will become an error in the future.

lib/matplotlib/table.py

@@ -24,6 +24,8 @@
 Thanks to John Gill for providing the class and table.
 """
 
+import numpy as np
+
 from . import _api, _docstring
 from .artist import Artist, allow_rasterization
 from .patches import Rectangle
@@ -494,14 +496,15 @@ def auto_set_column_width(self, col):
         col : int or sequence of ints
             The indices of the columns to auto-scale.
         """
-        # check for col possibility on iteration
-        try:
-            iter(col)
-        except (TypeError, AttributeError):
-            self._autoColumns.append(col)
-        else:
-            for cell in col:
-                self._autoColumns.append(cell)
+        col1d = np.atleast_1d(col)
+        if not np.issubdtype(col1d.dtype, np.integer):
+            _api.warn_deprecated("3.8", name="col",
+                                 message="%(name)r must be an int or sequence of ints. "
+                                 "Passing other types is deprecated since %(since)s "
+                                 "and will be removed %(removal)s.")
+            return
+        for cell in col1d:
+            self._autoColumns.append(cell)
 
         self.stale = True
 

lib/matplotlib/tests/test_table.py

@@ -1,9 +1,11 @@
-import matplotlib.pyplot as plt
 import numpy as np
-from matplotlib.testing.decorators import image_comparison, check_figures_equal
+import pytest
 
-from matplotlib.table import CustomCell, Table
+import matplotlib.pyplot as plt
+import matplotlib as mpl
 from matplotlib.path import Path
+from matplotlib.table import CustomCell, Table
+from matplotlib.testing.decorators import image_comparison, check_figures_equal
 from matplotlib.transforms import Bbox
 
 
@@ -176,7 +178,12 @@ def test_auto_column():
         loc="center")
     tb4.auto_set_font_size(False)
     tb4.set_fontsize(12)
-    tb4.auto_set_column_width("-101")
+    with pytest.warns(mpl.MatplotlibDeprecationWarning,
+                      match="'col' must be an int or sequence of ints"):
+        tb4.auto_set_column_width("-101")  # type: ignore [arg-type]
+    with pytest.warns(mpl.MatplotlibDeprecationWarning,
+                      match="'col' must be an int or sequence of ints"):
+        tb4.auto_set_column_width(["-101"])  # type: ignore [list-item]
 
 
 def test_table_cells():