From cfd768e7cd09257297645cba7f22bc10eff76c89 Mon Sep 17 00:00:00 2001
From: Antony Lee <anntzer.lee@gmail.com>
Date: Tue, 23 Apr 2019 22:53:30 +0200
Subject: [PATCH] Simpler "pyplotless" use pattern.

Right now, if one does not want to use pyplot (e.g., batch use), one can
do

    from matplotlib.figure import Figure
    fig = Figure(); ... <plot> ...; 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
    ... <plot> ...
    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")
    ... <plot> ...
    fig.savefig()
    plt.show([fig])
---
 lib/matplotlib/backend_bases.py | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
index 7f2ab50a56b2..caffc3ea647b 100644
--- a/lib/matplotlib/backend_bases.py
+++ b/lib/matplotlib/backend_bases.py
@@ -2485,19 +2485,23 @@ def key_press_handler(event, canvas=None, toolbar=None):
     toggle_xscale_keys = rcParams['keymap.xscale']
     all_keys = dict.__getitem__(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)
+    # quit all figures (no default)
     if event.key in quit_all_keys:
         Gcf.destroy_all()
 
+    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')
         if event.key in home_keys:
@@ -3545,15 +3549,16 @@ def draw_if_interactive(cls):
                 cls.trigger_manager_draw(manager)
 
     @classmethod
-    def show(cls, *, block=None):
+    def show(cls, figures=None, *, block=None):
         """
-        Show all figures.
+        Show the *figures*, defaulting to all pyplot-managed 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: