Property set and inherit backend_version.

It's not really clear if we really need to keep the backend_version
backend attribute, but currently it is getting overridden by
_Backend.export to "unknown" (as can be checked e.g. by printing
backend_agg.backend_version).  Move the definition to within the
_Backend class to fix that, and inherit that information where possible.

Author: anntzer

lib/matplotlib/backends/_backend_gtk.py

@@ -24,12 +24,7 @@
     raise ImportError("Gtk-based backends require cairo") from e
 
 _log = logging.getLogger(__name__)
-
-backend_version = "%s.%s.%s" % (
-    Gtk.get_major_version(), Gtk.get_minor_version(), Gtk.get_micro_version())
-
-# Placeholder
-_application = None
+_application = None  # Placeholder
 
 
 def _shutdown_application(app):
@@ -305,6 +300,12 @@ def trigger(self, *args):
 
 
 class _BackendGTK(_Backend):
+    backend_version = "%s.%s.%s" % (
+        Gtk.get_major_version(),
+        Gtk.get_minor_version(),
+        Gtk.get_micro_version(),
+    )
+
     @staticmethod
     def mainloop():
         global _application

lib/matplotlib/backends/_backend_tk.py

@@ -24,9 +24,6 @@
 
 
 _log = logging.getLogger(__name__)
-
-backend_version = tk.TkVersion
-
 cursord = {
     cursors.MOVE: "fleur",
     cursors.HAND: "hand2",
@@ -1017,6 +1014,7 @@ def trigger(self, *args):
 
 @_Backend.export
 class _BackendTk(_Backend):
+    backend_version = tk.TkVersion
     FigureManager = FigureManagerTk
 
     @staticmethod

lib/matplotlib/backends/backend_agg.py

@@ -40,9 +40,6 @@
 from matplotlib.backends._backend_agg import RendererAgg as _RendererAgg
 
 
-backend_version = 'v2.2'
-
-
 def get_hinting_flag():
     mapping = {
         'default': LOAD_DEFAULT,
@@ -563,5 +560,6 @@ def print_webp(self, filename_or_obj, *, pil_kwargs=None):
 
 @_Backend.export
 class _BackendAgg(_Backend):
+    backend_version = 'v2.2'
     FigureCanvas = FigureCanvasAgg
     FigureManager = FigureManagerBase

lib/matplotlib/backends/backend_cairo.py

@@ -34,9 +34,6 @@
 from matplotlib.transforms import Affine2D
 
 
-backend_version = cairo.version
-
-
 def _append_path(ctx, path, transform, clip=None):
     for points, code in path.iter_segments(
             transform, remove_nans=True, clip=clip):
@@ -548,5 +545,6 @@ def set_context(self, ctx):
 
 @_Backend.export
 class _BackendCairo(_Backend):
+    backend_version = cairo.version
     FigureCanvas = FigureCanvasCairo
     FigureManager = FigureManagerBase

lib/matplotlib/backends/backend_gtk3.py

@@ -31,7 +31,6 @@
     _BackendGTK, _FigureManagerGTK, _NavigationToolbar2GTK,
     TimerGTK as TimerGTK3,
 )
-from ._backend_gtk import backend_version  # noqa: F401 # pylint: disable=W0611
 
 
 _log = logging.getLogger(__name__)

lib/matplotlib/backends/backend_gtk4.py

@@ -28,7 +28,6 @@
     _BackendGTK, _FigureManagerGTK, _NavigationToolbar2GTK,
     TimerGTK as TimerGTK4,
 )
-from ._backend_gtk import backend_version  # noqa: F401 # pylint: disable=W0611
 
 
 class FigureCanvasGTK4(FigureCanvasBase, Gtk.DrawingArea):

lib/matplotlib/backends/backend_ps.py

@@ -33,9 +33,8 @@
 from matplotlib.backends.backend_mixed import MixedModeRenderer
 from . import _backend_pdf_ps
 
-_log = logging.getLogger(__name__)
 
-backend_version = 'Level II'
+_log = logging.getLogger(__name__)
 debugPS = False
 
 
@@ -1364,4 +1363,5 @@ def pstoeps(tmpfile, bbox=None, rotated=False):
 
 @_Backend.export
 class _BackendPS(_Backend):
+    backend_version = 'Level II'
     FigureCanvas = FigureCanvasPS

lib/matplotlib/backends/backend_qt.py

@@ -20,8 +20,6 @@
 )
 
 
-backend_version = __version__
-
 # SPECIAL_KEYS are Qt::Key that do *not* return their Unicode name
 # instead they have manually specified names.
 SPECIAL_KEYS = {
@@ -1013,6 +1011,7 @@ def trigger(self, *args, **kwargs):
 
 @_Backend.export
 class _BackendQT(_Backend):
+    backend_version = __version__
     FigureCanvas = FigureCanvasQT
     FigureManager = FigureManagerQT
 

lib/matplotlib/backends/backend_qt5.py

@@ -4,7 +4,7 @@
 
 
 from .backend_qt import (  # noqa
-    backend_version, SPECIAL_KEYS,
+    SPECIAL_KEYS,
     # Public API
     cursord, _create_qApp, _BackendQT, TimerQT, MainWindow, FigureCanvasQT,
     FigureManagerQT, ToolbarQt, NavigationToolbar2QT, SubplotToolQt,

lib/matplotlib/backends/backend_qt5agg.py

@@ -6,8 +6,7 @@
 backends._QT_FORCE_QT5_BINDING = True
 from .backend_qtagg import (    # noqa: F401, E402 # pylint: disable=W0611
     _BackendQTAgg, FigureCanvasQTAgg, FigureManagerQT, NavigationToolbar2QT,
-    backend_version,  FigureCanvasAgg,  FigureCanvasQT
-)
+    FigureCanvasAgg, FigureCanvasQT)
 
 
 @_BackendQTAgg.export