Fix #21409: Make twin axes inherit parent position

maf2310 · maf2310 · commit d9ef7af11bd6 · 2026-03-23T00:03:21.000Z
When set_position() is called before twinx() or twiny(),
the twin axes are created using the original subplot
position instead of the current position of the parent.

Set the twin position from the parent in _make_twin_axes
so that twins start aligned with the parent axes.

Add a regression test covering both twinx() and twiny().
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -4657,6 +4657,9 @@ def _make_twin_axes(self, *args, **kwargs):
         twin.set_zorder(self.zorder)
 
         self._twinned_axes.join(self, twin)
+
+        twin.set_position(self.get_position())
+
         return twin
 
     def twinx(self, axes_class=None, **kwargs):
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -477,6 +477,16 @@ def test_twin_inherit_autoscale_setting():
     assert not ax_y_off.get_autoscaley_on()
 
 
+@pytest.mark.parametrize("twin", ("x", "y"))
+def test_twin_respects_position_after_set_position(twin):
+    fig, ax = plt.subplots()
+
+    ax.set_position([0.2, 0.2, 0.5, 0.5])
+    ax2 = getattr(ax, f"twin{twin}")()
+
+    assert_allclose(ax.bbox.bounds, ax2.bbox.bounds)
+
+
 def test_inverted_cla():
     # GitHub PR #5450. Setting autoscale should reset
     # axes to be non-inverted.
