Deprecate add_subplot(<no positional args>) silently doing nothing.

anntzer · anntzer · commit 9eb7f87c9510 · 2019-01-13T22:56:31.000+01:00
To avoid head-scratching when `add_subplot(projection="3d")` does
nothing (the correct call is `add_subplot(111, projection="3d")`).
diff --git a/doc/api/next_api_changes/2018-01-09-AL.rst b/doc/api/next_api_changes/2018-01-09-AL.rst
@@ -0,0 +1,5 @@
+Behavior changes
+````````````````
+
+Calling `.Figure.add_subplot()` with no positional arguments used to do
+nothing; this now is equivalent to calling ``add_subplot(111)`` instead.
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -1311,14 +1311,14 @@ def add_subplot(self, *args, **kwargs):
         --------
         ::
 
-            fig=plt.figure()
+            fig = plt.figure()
             fig.add_subplot(221)
 
             # equivalent but more general
-            ax1=fig.add_subplot(2, 2, 1)
+            ax1 = fig.add_subplot(2, 2, 1)
 
             # add a subplot with no frame
-            ax2=fig.add_subplot(222, frameon=False)
+            ax2 = fig.add_subplot(222, frameon=False)
 
             # add a polar subplot
             fig.add_subplot(223, projection='polar')
@@ -1333,7 +1333,7 @@ def add_subplot(self, *args, **kwargs):
             fig.add_subplot(ax2)
         """
         if not len(args):
-            return
+            args = (1, 1, 1)
 
         if len(args) == 1 and isinstance(args[0], Integral):
             if not 100 <= args[0] <= 999:
diff --git a/lib/matplotlib/tests/test_figure.py b/lib/matplotlib/tests/test_figure.py
@@ -116,7 +116,7 @@ def test_clf_keyword():
 def test_figure():
     # named figure support
     fig = plt.figure('today')
-    ax = fig.add_subplot(111)
+    ax = fig.add_subplot()
     ax.set_title(fig.get_label())
     ax.plot(np.arange(5))
     # plot red line in a different figure.
