FIX: Reset label of axis to center (matplotlib#21773)

* Fix label shift and add test

* Use public api and revert changes

* Resolve ha conflict

* Allow ha overwrite

* Allow ha overwrite

* Allox x/y overwrite

* Fix bug

* Throw aliasing error

* Remove plt.close()

* Remove redundancy

* Call normalize_kwargs()

* Use setdefault()

* Use loc absent x, ha

Author: hansinahuja

lib/matplotlib/axes/_base.py

@@ -3487,15 +3487,19 @@ 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):
@@ -3831,15 +3835,19 @@ 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):

lib/matplotlib/tests/test_axes.py

@@ -105,6 +105,28 @@ 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)