From bb70b2afe39ad4334a9f3449cddd28149bd628b6 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Fri, 25 Dec 2020 17:04:26 +0200
Subject: [PATCH] bpo-15303: Support widgets with boolean value False in
 Tkinter (GH-23904)

Use `widget is None` instead of checking the boolean value of a widget.
---
 Lib/tkinter/__init__.py                       | 16 +++++++-------
 Lib/tkinter/commondialog.py                   |  2 +-
 Lib/tkinter/dnd.py                            | 22 +++++++++----------
 Lib/tkinter/font.py                           |  6 ++---
 Lib/tkinter/simpledialog.py                   |  4 ++--
 Lib/tkinter/tix.py                            |  6 ++---
 Lib/tkinter/ttk.py                            |  2 +-
 .../2020-12-21-22-59-26.bpo-15303.zozVrq.rst  |  1 +
 8 files changed, 30 insertions(+), 29 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2020-12-21-22-59-26.bpo-15303.zozVrq.rst

diff --git a/Lib/tkinter/__init__.py b/Lib/tkinter/__init__.py
index 1cc18704613..a32eb76d3b9 100644
--- a/Lib/tkinter/__init__.py
+++ b/Lib/tkinter/__init__.py
@@ -292,7 +292,7 @@ def _get_default_root(what=None):
     if not _support_default_root:
         raise RuntimeError("No master specified and tkinter is "
                            "configured to not support default root")
-    if not _default_root:
+    if _default_root is None:
         if what:
             raise RuntimeError(f"Too early to {what}: no default root window")
         root = Tk()
@@ -342,7 +342,7 @@ class Variable:
         if name is not None and not isinstance(name, str):
             raise TypeError("name must be a string")
         global _varnum
-        if not master:
+        if master is None:
             master = _get_default_root('create variable')
         self._root = master._root()
         self._tk = master.tk
@@ -808,7 +808,7 @@ class Misc:
         function which shall be called. Additional parameters
         are given as parameters to the function call.  Return
         identifier to cancel scheduling with after_cancel."""
-        if not func:
+        if func is None:
             # I'd rather use time.sleep(ms*0.001)
             self.tk.call('after', ms)
             return None
@@ -1542,7 +1542,7 @@ class Misc:
     def _root(self):
         """Internal function."""
         w = self
-        while w.master: w = w.master
+        while w.master is not None: w = w.master
         return w
     _subst_format = ('%#', '%b', '%f', '%h', '%k',
              '%s', '%t', '%w', '%x', '%y',
@@ -2306,7 +2306,7 @@ class Tk(Misc, Wm):
         self.tk.createcommand('exit', _exit)
         self._tclCommands.append('tkerror')
         self._tclCommands.append('exit')
-        if _support_default_root and not _default_root:
+        if _support_default_root and _default_root is None:
             _default_root = self
         self.protocol("WM_DELETE_WINDOW", self.destroy)
 
@@ -2534,7 +2534,7 @@ class BaseWidget(Misc):
 
     def _setup(self, master, cnf):
         """Internal function. Sets up information about children."""
-        if not master:
+        if master is None:
             master = _get_default_root()
         self.master = master
         self.tk = master.tk
@@ -3949,7 +3949,7 @@ class _setit:
 
     def __call__(self, *args):
         self.__var.set(self.__value)
-        if self.__callback:
+        if self.__callback is not None:
             self.__callback(self.__value, *args)
 
 
@@ -3998,7 +3998,7 @@ class Image:
 
     def __init__(self, imgtype, name=None, cnf={}, master=None, **kw):
         self.name = None
-        if not master:
+        if master is None:
             master = _get_default_root('create image')
         self.tk = getattr(master, 'tk', master)
         if not name:
diff --git a/Lib/tkinter/commondialog.py b/Lib/tkinter/commondialog.py
index cc3069842c3..12e42fe14ac 100644
--- a/Lib/tkinter/commondialog.py
+++ b/Lib/tkinter/commondialog.py
@@ -18,7 +18,7 @@ class Dialog:
     command = None
 
     def __init__(self, master=None, **options):
-        if not master:
+        if master is None:
             master = options.get('parent')
         self.master = master
         self.options = options
diff --git a/Lib/tkinter/dnd.py b/Lib/tkinter/dnd.py
index 3120ff342f8..acec61ba71f 100644
--- a/Lib/tkinter/dnd.py
+++ b/Lib/tkinter/dnd.py
@@ -108,7 +108,7 @@ __all__ = ["dnd_start", "DndHandler"]
 
 def dnd_start(source, event):
     h = DndHandler(source, event)
-    if h.root:
+    if h.root is not None:
         return h
     else:
         return None
@@ -143,7 +143,7 @@ class DndHandler:
     def __del__(self):
         root = self.root
         self.root = None
-        if root:
+        if root is not None:
             try:
                 del root.__dnd
             except AttributeError:
@@ -154,25 +154,25 @@ class DndHandler:
         target_widget = self.initial_widget.winfo_containing(x, y)
         source = self.source
         new_target = None
-        while target_widget:
+        while target_widget is not None:
             try:
                 attr = target_widget.dnd_accept
             except AttributeError:
                 pass
             else:
                 new_target = attr(source, event)
-                if new_target:
+                if new_target is not None:
                     break
             target_widget = target_widget.master
         old_target = self.target
         if old_target is new_target:
-            if old_target:
+            if old_target is not None:
                 old_target.dnd_motion(source, event)
         else:
-            if old_target:
+            if old_target is not None:
                 self.target = None
                 old_target.dnd_leave(source, event)
-            if new_target:
+            if new_target is not None:
                 new_target.dnd_enter(source, event)
                 self.target = new_target
 
@@ -193,7 +193,7 @@ class DndHandler:
             self.initial_widget.unbind("<Motion>")
             widget['cursor'] = self.save_cursor
             self.target = self.source = self.initial_widget = self.root = None
-            if target:
+            if target is not None:
                 if commit:
                     target.dnd_commit(source, event)
                 else:
@@ -215,9 +215,9 @@ class Icon:
         if canvas is self.canvas:
             self.canvas.coords(self.id, x, y)
             return
-        if self.canvas:
+        if self.canvas is not None:
             self.detach()
-        if not canvas:
+        if canvas is None:
             return
         label = tkinter.Label(canvas, text=self.name,
                               borderwidth=2, relief="raised")
@@ -229,7 +229,7 @@ class Icon:
 
     def detach(self):
         canvas = self.canvas
-        if not canvas:
+        if canvas is None:
             return
         id = self.id
         label = self.label
diff --git a/Lib/tkinter/font.py b/Lib/tkinter/font.py
index c051162bd29..7f6ba5a80fb 100644
--- a/Lib/tkinter/font.py
+++ b/Lib/tkinter/font.py
@@ -68,7 +68,7 @@ class Font:
 
     def __init__(self, root=None, font=None, name=None, exists=False,
                  **options):
-        if not root:
+        if root is None:
             root = tkinter._get_default_root('use font')
         tk = getattr(root, 'tk', root)
         if font:
@@ -183,7 +183,7 @@ class Font:
 
 def families(root=None, displayof=None):
     "Get font families (as a tuple)"
-    if not root:
+    if root is None:
         root = tkinter._get_default_root('use font.families()')
     args = ()
     if displayof:
@@ -193,7 +193,7 @@ def families(root=None, displayof=None):
 
 def names(root=None):
     "Get names of defined fonts (as a tuple)"
-    if not root:
+    if root is None:
         root = tkinter._get_default_root('use font.names()')
     return root.tk.splitlist(root.tk.call("font", "names"))
 
diff --git a/Lib/tkinter/simpledialog.py b/Lib/tkinter/simpledialog.py
index 638da87c876..d9762b1351a 100644
--- a/Lib/tkinter/simpledialog.py
+++ b/Lib/tkinter/simpledialog.py
@@ -99,7 +99,7 @@ class Dialog(Toplevel):
             title -- the dialog title
         '''
         master = parent
-        if not master:
+        if master is None:
             master = _get_default_root('create dialog window')
 
         Toplevel.__init__(self, master)
@@ -124,7 +124,7 @@ class Dialog(Toplevel):
 
         self.buttonbox()
 
-        if not self.initial_focus:
+        if self.initial_focus is None:
             self.initial_focus = self
 
         self.protocol("WM_DELETE_WINDOW", self.cancel)
diff --git a/Lib/tkinter/tix.py b/Lib/tkinter/tix.py
index ef1e7406bc1..7d240754036 100644
--- a/Lib/tkinter/tix.py
+++ b/Lib/tkinter/tix.py
@@ -386,7 +386,7 @@ class TixWidget(tkinter.Widget):
             self.tk.call(name, 'configure', '-' + option, value)
     # These are missing from Tkinter
     def image_create(self, imgtype, cnf={}, master=None, **kw):
-        if not master:
+        if master is None:
             master = self
         if kw and cnf: cnf = _cnfmerge((cnf, kw))
         elif kw: cnf = kw
@@ -467,7 +467,7 @@ class DisplayStyle:
     (multiple) Display Items"""
 
     def __init__(self, itemtype, cnf={}, *, master=None, **kw):
-        if not master:
+        if master is None:
             if 'refwindow' in kw:
                 master = kw['refwindow']
             elif 'refwindow' in cnf:
@@ -862,7 +862,7 @@ class HList(TixWidget, XView, YView):
         return self.tk.call(self._w, 'add', entry, *self._options(cnf, kw))
 
     def add_child(self, parent=None, cnf={}, **kw):
-        if not parent:
+        if parent is None:
             parent = ''
         return self.tk.call(
                      self._w, 'addchild', parent, *self._options(cnf, kw))
diff --git a/Lib/tkinter/ttk.py b/Lib/tkinter/ttk.py
index ab7aeb15e8f..b854235a626 100644
--- a/Lib/tkinter/ttk.py
+++ b/Lib/tkinter/ttk.py
@@ -569,7 +569,7 @@ class Widget(tkinter.Widget):
         matches statespec. statespec is expected to be a sequence."""
         ret = self.tk.getboolean(
                 self.tk.call(self._w, "instate", ' '.join(statespec)))
-        if ret and callback:
+        if ret and callback is not None:
             return callback(*args, **kw)
 
         return ret
diff --git a/Misc/NEWS.d/next/Library/2020-12-21-22-59-26.bpo-15303.zozVrq.rst b/Misc/NEWS.d/next/Library/2020-12-21-22-59-26.bpo-15303.zozVrq.rst
new file mode 100644
index 00000000000..5a7900aa909
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-12-21-22-59-26.bpo-15303.zozVrq.rst
@@ -0,0 +1 @@
+:mod:`tkinter` supports now widgets with boolean value False.