Backport PR #28292: Resolve MaxNLocator IndexError when no large steps

tacaswell · meeseeksmachine · commit 623445641b3a · 2024-06-02T14:47:40.000Z
diff --git a/lib/matplotlib/tests/test_ticker.py b/lib/matplotlib/tests/test_ticker.py
@@ -130,6 +130,14 @@ def test_view_limits_round_numbers_with_offset(self):
             loc = mticker.MultipleLocator(base=3.147, offset=1.3)
             assert_almost_equal(loc.view_limits(-4, 4), (-4.994, 4.447))
 
+    def test_view_limits_single_bin(self):
+        """
+        Test that 'round_numbers' works properly with a single bin.
+        """
+        with mpl.rc_context({'axes.autolimit_mode': 'round_numbers'}):
+            loc = mticker.MaxNLocator(nbins=1)
+            assert_almost_equal(loc.view_limits(-2.3, 2.3), (-4, 4))
+
     def test_set_params(self):
         """
         Create multiple locator with 0.7 base, and change it to something else.
diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
@@ -2137,7 +2137,10 @@ def _raw_ticks(self, vmin, vmax):
             large_steps = large_steps & (floored_vmaxs >= _vmax)
 
         # Find index of smallest large step
-        istep = np.nonzero(large_steps)[0][0]
+        if any(large_steps):
+            istep = np.nonzero(large_steps)[0][0]
+        else:
+            istep = len(steps) - 1
 
         # Start at smallest of the steps greater than the raw step, and check
         # if it provides enough ticks. If not, work backwards through
