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Fix #21409: Make twin axes inherit parent position #31353

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Merged
QuLogic merged 7 commits into from
Apr 10, 2026
+50 −0
Merged

Fix #21409: Make twin axes inherit parent position #31353

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d9ef7af
Fix #21409: Make twin axes inherit parent position
maf2310 Mar 23, 2026
88d4ec5
Refine twin position fix to preserve layout participation
maf2310 Mar 24, 2026
a5435b5
Address review: preserve original/active positions and fix test + lint
maf2310 Mar 25, 2026
ce749b4
Clarify manual-position twin sync in code comment
maf2310 Mar 25, 2026
5876d06
Add regression test for twinx top spine position
maf2310 Mar 27, 2026
e8df9e5
Add test to ensure twin axes remain aligned after tight_layout
maf2310 Mar 29, 2026
c2a343c
Add tests for twin axes alignment with manual positioning_layout
maf2310 Mar 30, 2026
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14 changes: 14 additions & 0 deletions lib/matplotlib/axes/_base.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4657,6 +4657,20 @@ def _make_twin_axes(self, *args, **kwargs):
twin.set_zorder(self.zorder)

self._twinned_axes.join(self, twin)

# If the parent Axes has been manually positioned (set_position() sets
# in_layout=False), the SubplotSpec-based add_subplot(...) path ignores
# that manual position when creating a twin. In that case, explicitly
# copy both the original and active positions to the twin so they start
# aligned.
#
# For layout-managed Axes (in_layout=True), we keep the existing
# SubplotSpec-driven behavior, so layout engines such as tight_layout
# and constrained_layout continue to control positioning.
if not self.get_in_layout():
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@jklymak jklymak Mar 27, 2026

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I think this is all fine, but needs to be tested.

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@maf2310 maf2310 Mar 27, 2026

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Thanks! I’ll add additional tests to cover this case.

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@maf2310 maf2310 Mar 27, 2026

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I added tests to cover both manual positioning and layout-managed cases. Let me know if anything else should be tested.

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@jklymak jklymak Mar 29, 2026

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I'd prefer an actual test that the positions match after layout is applied.

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@maf2310 maf2310 Mar 29, 2026

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ok, I'll add it

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@maf2310 maf2310 Mar 29, 2026

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I added a test that explicitly checks that the twin and parent positions
still match after tight_layout() is applied.
Let me know if I should add anything else.

twin._set_position(self.get_position(original=True), which="original")
twin._set_position(self.get_position(original=False), which="active")

return twin

def twinx(self, axes_class=None, **kwargs):
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10 changes: 10 additions & 0 deletions lib/matplotlib/tests/test_axes.py
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Expand Up @@ -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.get_position().bounds, ax2.get_position().bounds)


def test_inverted_cla():
# GitHub PR #5450. Setting autoscale should reset
# axes to be non-inverted.
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