FIX: set sca when re-using as Axes with pyplot.subplot

Author: tacaswell

lib/matplotlib/pyplot.py

@@ -1232,6 +1232,7 @@ def subplot(*args, **kwargs):
     # If no existing axes match, then create a new one.
     if ax is None:
         ax = fig.add_subplot(*args, **kwargs)
+    fig.sca(ax)
 
     bbox = ax.bbox
     axes_to_delete = []

lib/matplotlib/tests/test_pyplot.py

@@ -161,3 +161,12 @@ def test_close():
     except TypeError as e:
         assert str(e) == "close() argument must be a Figure, an int, " \
                          "a string, or None, not <class 'float'>"
+
+
+def test_subplot_reuse():
+    ax1 = plt.subplot(121)
+    assert ax1 is plt.gca()
+    ax2 = plt.subplot(122)
+    assert ax2 is plt.gca()
+    ax1 = plt.subplot(121)
+    assert ax1 is plt.gca()