Fix default label visibility for top-or-left-labeled shared subplots().

On the following example
```python
from pylab import *
rcParams.update({"xtick.labeltop": 1, "xtick.labelbottom": 0,
                 "ytick.labelright": 1, "ytick.labelleft": 0})
subplots(3, 3, sharex=True, sharey=True)
```
subplots() now correctly leaves the xlabels on the first row and the
ylabels on the last column, rather than the other way round.

On the following example
```python
from pylab import *
rcParams.update({"xtick.labeltop": 1, "xtick.labelbottom": 1,
                 "ytick.labelright": 1, "ytick.labelleft": 1})
subplots(3, 3, sharex=True, sharey=True)
show()
```
subplots() now correctly leaves the xlabels on the first and last row
and the ylabels on the first and last column.

Author: anntzer

doc/users/next_whats_new/top-left-shared-subplots.rst

@@ -0,0 +1,10 @@
+Shared-axes ``subplots`` tick label visibility is now correct for top or left labels
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When calling ``subplots(..., sharex=True, sharey=True)``, Matplotlib
+automatically hides x tick labels for axes not in the first column and y tick
+labels for axes not in the last row.  This behavior is incorrect if rcParams
+specify that axes should be labeled on the top (``rcParams["xtick.labeltop"] =
+True``) or on the right (``rcParams["ytick.labelright"] = True``).
+
+Such cases are now handled correctly (adjusting visibility as needed on the
+first row and last column of axes).

lib/matplotlib/gridspec.py

@@ -309,17 +309,23 @@ def subplots(self, *, sharex=False, sharey=False, squeeze=True,
 
         # turn off redundant tick labeling
         if sharex in ["col", "all"]:
-            # turn off all but the bottom row
-            for ax in axarr[:-1, :].flat:
-                ax.xaxis.set_tick_params(which='both',
-                                         labelbottom=False, labeltop=False)
-                ax.xaxis.offsetText.set_visible(False)
+            for ax in axarr[:-1, :].flat:  # Remove bottom labels/offsettexts.
+                ax.xaxis.set_tick_params(which="both", labelbottom=False)
+                if ax.xaxis.offsetText.get_position()[1] == 0:
+                    ax.xaxis.offsetText.set_visible(False)
+            for ax in axarr[1:, :].flat:  # Remove top labels/offsettexts.
+                ax.xaxis.set_tick_params(which="both", labeltop=False)
+                if ax.xaxis.offsetText.get_position()[1] == 1:
+                    ax.xaxis.offsetText.set_visible(False)
         if sharey in ["row", "all"]:
-            # turn off all but the first column
-            for ax in axarr[:, 1:].flat:
-                ax.yaxis.set_tick_params(which='both',
-                                         labelleft=False, labelright=False)
-                ax.yaxis.offsetText.set_visible(False)
+            for ax in axarr[:, 1:].flat:  # Remove left labels/offsettexts.
+                ax.yaxis.set_tick_params(which="both", labelleft=False)
+                if ax.yaxis.offsetText.get_position()[0] == 0:
+                    ax.yaxis.offsetText.set_visible(False)
+            for ax in axarr[:, :-1].flat:  # Remove right labels/offsettexts.
+                ax.yaxis.set_tick_params(which="both", labelright=False)
+                if ax.yaxis.offsetText.get_position()[0] == 1:
+                    ax.yaxis.offsetText.set_visible(False)
 
         if squeeze:
             # Discarding unneeded dimensions that equal 1.  If we only have one

lib/matplotlib/tests/test_subplots.py

@@ -160,6 +160,28 @@ def test_subplots_offsettext():
     axs[1, 1].plot(y, x)
 
 
+@pytest.mark.parametrize("top", [True, False])
+@pytest.mark.parametrize("bottom", [True, False])
+@pytest.mark.parametrize("left", [True, False])
+@pytest.mark.parametrize("right", [True, False])
+def test_subplots_hide_labels(top, bottom, left, right):
+    # Ideally, we would also test offset-text visibility (and remove
+    # test_subplots_offsettext), but currently, setting rcParams fails to move
+    # the offset texts as well.
+    with plt.rc_context({"xtick.labeltop": top, "xtick.labelbottom": bottom,
+                         "ytick.labelleft": left, "ytick.labelright": right}):
+        axs = plt.figure().subplots(3, 3, sharex=True, sharey=True)
+    for (i, j), ax in np.ndenumerate(axs):
+        xtop = ax.xaxis._major_tick_kw["label2On"]
+        xbottom = ax.xaxis._major_tick_kw["label1On"]
+        yleft = ax.yaxis._major_tick_kw["label1On"]
+        yright = ax.yaxis._major_tick_kw["label2On"]
+        assert xtop == (top and i == 0)
+        assert xbottom == (bottom and i == 2)
+        assert yleft == (left and j == 0)
+        assert yright == (right and j == 2)
+
+
 def test_get_gridspec():
     # ahem, pretty trivial, but...
     fig, ax = plt.subplots()