Simpler "pyplotless" use pattern.

anntzer · anntzer · commit 2980caa369e6 · 2019-04-24T10:44:15.000+02:00
Right now, if one does not want to use pyplot (e.g., batch use), one can
do

    from matplotlib.figure import Figure
    fig = Figure(); ... &lt;plot&gt; ...; fig.savefig(...)

but it is impossible to show() the figure interactively (i.e. pyplot
cannot "adopt" the figure) e.g. for debugging.

This patch makes it possible: with it, one can do

    fig = plt.new_figure_manager(num).canvas.figure
    ... &lt;plot&gt; ...
    fig.savefig()
    plt.show(figures=[fig])

Note that this does *not* register the figure with pyplot; in particular
*fig* is garbage-collected when it goes out of scope, does not
participate in gcf(); etc.  So this is "pyplotless" in the sense that
there is no global figure registry anymore, but pyplot still stays in
charge of the GUI integration.

Obviously the `plt.new_figure_manager(num).canvas.figure` expression
could / should be encapsulated in a helper function, up to bikeshedding.

The `num` parameter is needed as matplotlib currently uses it to set the
figure title, but that can easily be made optional too.

Finally note that `plt.show([fig])` would be a nicer API, but right now
the first parameter to plt.show is `block`, which is undergoing
transition to kwonly.

IOW the end-goal would be e.g.

    # intentionally terrible name as placeholder :)
    fig = plt.new_figure_not_globally_registered("some title")
    ... &lt;plot&gt; ...
    fig.savefig()
    plt.show([fig])
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -2300,16 +2300,18 @@ def key_press_handler(event, canvas, toolbar=None):
     toggle_xscale_keys = rcParams['keymap.xscale']
     all_keys = rcParams['keymap.all_axes']
 
-    # toggle fullscreen mode ('f', 'ctrl + f')
-    if event.key in fullscreen_keys:
-        try:
-            canvas.manager.full_screen_toggle()
-        except AttributeError:
-            pass
+    manager = canvas.manager
 
-    # quit the figure (default key 'ctrl+w')
-    if event.key in quit_keys:
-        Gcf.destroy_fig(canvas.figure)
+    if manager is not None:
+        # toggle fullscreen mode ('f', 'ctrl + f')
+        if event.key in fullscreen_keys:
+            canvas.manager.full_screen_toggle()
+        # quit the figure (default key 'ctrl+w')
+        if event.key in quit_keys:
+            if Gcf.get_fig_manager(canvas.manager.num):
+                Gcf.destroy_fig(canvas.figure)
+            else:
+                manager.destroy()
 
     if toolbar is not None:
         # home or reset mnemonic  (default key 'h', 'home' and 'r')
@@ -3264,15 +3266,16 @@ def draw_if_interactive(cls):
 
     @classmethod
     @cbook._make_keyword_only("3.1", "block")
-    def show(cls, block=None):
+    def show(cls, block=None, *, figures=None):
         """
         Show all figures.
 
         `show` blocks by calling `mainloop` if *block* is ``True``, or if it
         is ``None`` and we are neither in IPython's ``%pylab`` mode, nor in
         `interactive` mode.
         """
-        managers = Gcf.get_all_fig_managers()
+        managers = ([figure.canvas.manager for figure in figures]
+                    if figures is not None else Gcf.get_all_fig_managers())
         if not managers:
             return
         for manager in managers:
