matplotlib · tacaswell · Jan 5, 2016 · Jan 27, 2016 · Jan 27, 2016 · Jul 14, 2020
diff --git a/doc/api/next_api_changes/behavior/17923-TAC.rst b/doc/api/next_api_changes/behavior/17923-TAC.rst
@@ -0,0 +1,20 @@
+Make ``draw_idle`` method on ``FigureCanvasBase`` a no-op if not in interactive mode
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+For backends that do not have an event loop associated with them
+(e.g. non-GUI backends) the semantics of `.FigureCanvasBase.draw_idle` are
+not clear.  Previously it was equivalent to a non-re-entrant
+``fig.canvas.draw()`` call in all cases.  Now it will be a no-op
+unless Matplotlib is in "interactive mode" (as given by
+`matplotlib.is_interactive`).
+
+There are a number of derived properties in the Figure that we defer
+computing until draw time (limits, ticks, the size of things in screen
+space, optimized layout, etc).  If you need to be sure that these
+values are correct (with any backend) call ::
+
+  fig.draw_no_output()
+
+to force the Figure to fully render.  This may break user code if it
+is relying on `pyplot.draw` (which internally calls ``draw_idle``)
+for the same effect in non-interactive mode.
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -2054,7 +2054,7 @@ def draw_idle(self, *args, **kwargs):
        strategy to prevent multiple renderings.

        """
-        if not self._is_idle_drawing:
+        if is_interactive() and not self._is_idle_drawing:
            with self._idle_draw_cntx():
                self.draw(*args, **kwargs)


diff --git a/lib/matplotlib/tests/test_agg.py b/lib/matplotlib/tests/test_agg.py
@@ -208,13 +208,13 @@ def test_chunksize():
    # Test without chunksize
    fig, ax = plt.subplots()
    ax.plot(x, np.sin(x))
-    fig.canvas.draw()
+    fig.draw_no_output()

    # Test with chunksize
    fig, ax = plt.subplots()
    rcParams['agg.path.chunksize'] = 105
    ax.plot(x, np.sin(x))
-    fig.canvas.draw()
+    fig.draw_no_output()


 @pytest.mark.backend('Agg')
@@ -250,4 +250,5 @@ def test_draw_path_collection_error_handling():
    fig, ax = plt.subplots()
    ax.scatter([1], [1]).set_paths(path.Path([(0, 1), (2, 3)]))
    with pytest.raises(TypeError):
+        # this needs to exercise code in the render paths
        fig.canvas.draw()
diff --git a/lib/matplotlib/tests/test_animation.py b/lib/matplotlib/tests/test_animation.py
@@ -358,7 +358,8 @@ def animate(i):
            return return_value

    with pytest.raises(RuntimeError):
-        animation.FuncAnimation(fig, animate, blit=True)
+        anim = animation.FuncAnimation(fig, animate, blit=True)
+        fig.draw_no_output()


 def test_exhausted_animation(tmpdir):

diff --git a/lib/matplotlib/tests/test_artist.py b/lib/matplotlib/tests/test_artist.py
@@ -193,7 +193,7 @@ def test_remove():
    assert fig.stale
    assert ax.stale

-    fig.canvas.draw()
+    fig.draw_no_output()
    assert not fig.stale
    assert not ax.stale
    assert not ln.stale