Backport PR #21773: FIX: Reset label of axis to center

hansinahuja · meeseeksmachine · commit 108448319ba0 · 2021-12-10T05:27:33.000Z
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -3488,15 +3488,19 @@ def set_xlabel(self, xlabel, fontdict=None, labelpad=None, *,
                                 f"its corresponding low level keyword "
                                 f"arguments ({protected_kw}) are also "
                                 f"supplied")
-            loc = 'center'
+
         else:
             loc = (loc if loc is not None
                    else mpl.rcParams['xaxis.labellocation'])
-        _api.check_in_list(('left', 'center', 'right'), loc=loc)
-        if loc == 'left':
-            kwargs.update(x=0, horizontalalignment='left')
-        elif loc == 'right':
-            kwargs.update(x=1, horizontalalignment='right')
+            _api.check_in_list(('left', 'center', 'right'), loc=loc)
+
+            if loc == 'left':
+                kwargs.update(x=0, horizontalalignment='left')
+            elif loc == 'center':
+                kwargs.update(x=0.5, horizontalalignment='center')
+            elif loc == 'right':
+                kwargs.update(x=1, horizontalalignment='right')
+
         return self.xaxis.set_label_text(xlabel, fontdict, **kwargs)
 
     def invert_xaxis(self):
@@ -3832,15 +3836,19 @@ def set_ylabel(self, ylabel, fontdict=None, labelpad=None, *,
                                 f"its corresponding low level keyword "
                                 f"arguments ({protected_kw}) are also "
                                 f"supplied")
-            loc = 'center'
+
         else:
             loc = (loc if loc is not None
                    else mpl.rcParams['yaxis.labellocation'])
-        _api.check_in_list(('bottom', 'center', 'top'), loc=loc)
-        if loc == 'bottom':
-            kwargs.update(y=0, horizontalalignment='left')
-        elif loc == 'top':
-            kwargs.update(y=1, horizontalalignment='right')
+            _api.check_in_list(('bottom', 'center', 'top'), loc=loc)
+
+            if loc == 'bottom':
+                kwargs.update(y=0, horizontalalignment='left')
+            elif loc == 'center':
+                kwargs.update(y=0.5, horizontalalignment='center')
+            elif loc == 'top':
+                kwargs.update(y=1, horizontalalignment='right')
+
         return self.yaxis.set_label_text(ylabel, fontdict, **kwargs)
 
     def invert_yaxis(self):
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -104,6 +104,28 @@ def test_label_loc_rc(fig_test, fig_ref):
     cbar.set_label("Z Label", x=1, ha='right')
 
 
+def test_label_shift():
+    fig, ax = plt.subplots()
+
+    # Test label re-centering on x-axis
+    ax.set_xlabel("Test label", loc="left")
+    ax.set_xlabel("Test label", loc="center")
+    assert ax.xaxis.get_label().get_horizontalalignment() == "center"
+    ax.set_xlabel("Test label", loc="right")
+    assert ax.xaxis.get_label().get_horizontalalignment() == "right"
+    ax.set_xlabel("Test label", loc="center")
+    assert ax.xaxis.get_label().get_horizontalalignment() == "center"
+
+    # Test label re-centering on y-axis
+    ax.set_ylabel("Test label", loc="top")
+    ax.set_ylabel("Test label", loc="center")
+    assert ax.yaxis.get_label().get_horizontalalignment() == "center"
+    ax.set_ylabel("Test label", loc="bottom")
+    assert ax.yaxis.get_label().get_horizontalalignment() == "left"
+    ax.set_ylabel("Test label", loc="center")
+    assert ax.yaxis.get_label().get_horizontalalignment() == "center"
+
+
 @check_figures_equal(extensions=["png"])
 def test_acorr(fig_test, fig_ref):
     np.random.seed(19680801)
