Qt: Misc. refactor in __init__.py, ElectrumGui class

Made the code slightly simpler by detecting macOS version in precisely
only one place. Also updated some comments to use the preferred """
syntax for function comments.

electroncash_gui/qt/__init__.py

@@ -188,19 +188,23 @@ def my_do_in_main_thread_handler(func, *args, **kwargs):
         Handlers.do_in_main_thread = my_do_in_main_thread_handler
 
     def _do_in_main_thread_handler_slot(self, func, args, kwargs):
-        ''' Hooked in to util.Handlers.do_in_main_thread via the
+        """
+        Hooked in to util.Handlers.do_in_main_thread via the
         do_in_main_thread_signal. This ensures that there is an app-wide
         mechanism for posting invocations to the main thread.  Currently
-        CashFusion uses this mechanism, but other code may as well. '''
+        CashFusion uses this mechanism, but other code may as well.
+        """
         func(*args, **kwargs)
 
     def _pre_and_post_app_setup(self):
-        ''' Call this before instantiating the QApplication object.  It sets up
+        """
+        Call this before instantiating the QApplication object.  It sets up
         some platform-specific miscellany that need to happen before the
         QApplication is constructed.
 
         A function is returned.  This function *must* be called after the
-        QApplication is constructed. '''
+        QApplication is constructed.
+        """
         callables = []
         def call_callables():
             for func in callables:
@@ -240,51 +244,41 @@ def call_callables():
         if hasattr(Qt, "AA_UseHighDpiPixmaps"):
             QCoreApplication.setAttribute(Qt.AA_UseHighDpiPixmaps)
 
+        # Set mac_ver to the appropriate macOS version e.g.: (10,15,1) for Catalina, etc or None if not macOS
+        mac_ver = None
+        if sys.platform in ('darwin',):
+            try:
+                mac_ver = tuple(int(a) for a in platform.mac_ver()[0].split('.'))
+                self.print_error("macOS version:", mac_ver)
+            except (TypeError, ValueError) as e:
+                self.print_error("WARNING: Cannot parse platform.mac_ver:", repr(e))
+
         # macOS Mojave "font rendering looks terrible on PyQt5.11" workaround.
         # See: https://old.reddit.com/r/apple/comments/9leavs/fix_mojave_font_rendering_issues_on_a_perapp_basis/
         # This affects PyQt 5.11 (which is what we ship in the macOS El Capitan
         # .dmg).  We apply the workaround and also warn the user to not use
         # the El Capitan compatibility .dmg.
-        if sys.platform in ('darwin',) and self.qt_version() < (5, 12):
+        if mac_ver and mac_ver >= (10, 14) and self.qt_version() < (5, 12):
             # macOS hacks. On Mojave with PyQt <5.12 the font rendering is terrible.
             # As a workaround we need to temporarily set this 'defaults' keys
             # which we immediately disable after the QApplication is started.
-            try:
-                ver = tuple(int(a) for a in platform.mac_ver()[0].split('.'))
-            except (TypeError, ValueError):
-                self.print_error("WARNING: Cannot parse platform.mac_ver", f"'{platform.mac_ver()[0]}'")
-                ver = None
-            if ver and ver >= (10, 14):
-                from electroncash.utils import macos
-                self.print_error("Mojave+ with PyQt<5.12 detected; applying CGFontRenderingFontSmoothingDisabled workaround...")
-                bundle = macos.get_bundle_identifier()
-                os.system(f'defaults write {bundle} CGFontRenderingFontSmoothingDisabled -bool NO')
-                def undo_hack():
-                    os.system(f'defaults delete {bundle} CGFontRenderingFontSmoothingDisabled')
-                    self.print_error("Mojave+ font rendering workaround applied.")
-                    #msg = _("Mojave or newer system detected, however you are running the "
-                    #        "El Capitan compatibility release of Electron Cash. "
-                    #        "Font and graphics rendering may be affected."
-                    #        "\n\nPlease obtain the latest non-compatibility version "
-                    #        "of Electron Cash for MacOS.")
-                    #QMessageBox.warning(None, _("Warning"), msg)  # this works even if app is not exec_() yet.
-
-                callables.append(undo_hack)
+            from electroncash.utils import macos
+            self.print_error("Mojave+ with PyQt<5.12 detected; applying CGFontRenderingFontSmoothingDisabled workaround...")
+            bundle = macos.get_bundle_identifier()
+            os.system(f'defaults write {bundle} CGFontRenderingFontSmoothingDisabled -bool NO')
+            def undo_hack():
+                os.system(f'defaults delete {bundle} CGFontRenderingFontSmoothingDisabled')
+                self.print_error("Mojave+ font rendering workaround applied.")
+
+            callables.append(undo_hack)
 
         # macOS Big Sur workaround for Qt>=5.13.2 sometimes not working at all
         # See: https://bugreports.qt.io/browse/QTBUG-87014
         # See also: https://stackoverflow.com/questions/64818879/is-there-any-solution-regarding-to-pyqt-library-doesnt-work-in-mac-os-big-sur
-        if sys.platform in ('darwin', ):
-            try:
-                release_tuple = version.normalize_version(platform.uname().release)
-                self.print_error("Darwin kernel version:", '.'.join([str(x) for x in release_tuple]))
-            except Exception as e:
-                release_tuple = (0, 0, 0)
-                self.print_error("Error parsing Darwin kernel version:", repr(e))
-            if release_tuple >= (20, 0, 0) and self.qt_version() > (5, 13, 1):
-                # Setting this env var causes Qt to use some other macOS API that always works on Big Sur
-                os.environ['QT_MAC_WANTS_LAYER'] = '1'
-                self.print_error(f"macOS Big Sur Qt workaround applied")
+        if mac_ver and mac_ver >= (10, 16) and self.qt_version() >= (5, 13, 2):
+            # Setting this env var causes Qt to use some other macOS API that always works on Big Sur
+            os.environ['QT_MAC_WANTS_LAYER'] = '1'
+            self.print_error(f"macOS Big Sur Qt workaround applied")
 
         def setup_layout_direction():
             """Sets the app layout direction depending on language. To be called