bpo-42685: Improve placing of simple query windows. (GH-23856)

* If parent is specified and mapped, the query widget is
  centered at the center of parent. Its position and size
  can be corrected so that it fits in the virtual root window.
* Otherwise it is centered at the center of the screen.

Lib/tkinter/simpledialog.py

@@ -55,36 +55,8 @@ def __init__(self, master,
                 b.config(relief=RIDGE, borderwidth=8)
             b.pack(side=LEFT, fill=BOTH, expand=1)
         self.root.protocol('WM_DELETE_WINDOW', self.wm_delete_window)
-        self._set_transient(master)
-
-    def _set_transient(self, master, relx=0.5, rely=0.3):
-        widget = self.root
-        widget.withdraw() # Remain invisible while we figure out the geometry
-        widget.transient(master)
-        widget.update_idletasks() # Actualize geometry information
-        if master.winfo_ismapped():
-            m_width = master.winfo_width()
-            m_height = master.winfo_height()
-            m_x = master.winfo_rootx()
-            m_y = master.winfo_rooty()
-        else:
-            m_width = master.winfo_screenwidth()
-            m_height = master.winfo_screenheight()
-            m_x = m_y = 0
-        w_width = widget.winfo_reqwidth()
-        w_height = widget.winfo_reqheight()
-        x = m_x + (m_width - w_width) * relx
-        y = m_y + (m_height - w_height) * rely
-        if x+w_width > master.winfo_screenwidth():
-            x = master.winfo_screenwidth() - w_width
-        elif x < 0:
-            x = 0
-        if y+w_height > master.winfo_screenheight():
-            y = master.winfo_screenheight() - w_height
-        elif y < 0:
-            y = 0
-        widget.geometry("+%d+%d" % (x, y))
-        widget.deiconify() # Become visible at the desired location
+        self.root.transient(master)
+        _place_window(self.root, master)
 
     def go(self):
         self.root.wait_visibility()
@@ -157,11 +129,7 @@ def __init__(self, parent, title = None):
 
         self.protocol("WM_DELETE_WINDOW", self.cancel)
 
-        if parent is not None:
-            self.geometry("+%d+%d" % (parent.winfo_rootx()+50,
-                                      parent.winfo_rooty()+50))
-
-        self.deiconify() # become visible now
+        _place_window(self, parent)
 
         self.initial_focus.focus_set()
 
@@ -251,6 +219,37 @@ def apply(self):
         pass # override
 
 
+# Place a toplevel window at the center of parent or screen
+# It is a Python implementation of ::tk::PlaceWindow.
+def _place_window(w, parent=None):
+    w.wm_withdraw() # Remain invisible while we figure out the geometry
+    w.update_idletasks() # Actualize geometry information
+
+    minwidth = w.winfo_reqwidth()
+    minheight = w.winfo_reqheight()
+    maxwidth = w.winfo_vrootwidth()
+    maxheight = w.winfo_vrootheight()
+    if parent is not None and parent.winfo_ismapped():
+        x = parent.winfo_rootx() + (parent.winfo_width() - minwidth) // 2
+        y = parent.winfo_rooty() + (parent.winfo_height() - minheight) // 2
+        vrootx = w.winfo_vrootx()
+        vrooty = w.winfo_vrooty()
+        x = min(x, vrootx + maxwidth - minwidth)
+        x = max(x, vrootx)
+        y = min(y, vrooty + maxheight - minheight)
+        y = max(y, vrooty)
+        if w._windowingsystem == 'aqua':
+            # Avoid the native menu bar which sits on top of everything.
+            y = max(y, 22)
+    else:
+        x = (w.winfo_screenwidth() - minwidth) // 2
+        y = (w.winfo_screenheight() - minheight) // 2
+
+    w.wm_maxsize(maxwidth, maxheight)
+    w.wm_geometry('+%d+%d' % (x, y))
+    w.wm_deiconify() # Become visible at the desired location
+
+
 # --------------------------------------------------------------------
 # convenience dialogues
 

Misc/NEWS.d/next/Library/2020-12-19-17-32-43.bpo-42685.kwZlwp.rst

@@ -0,0 +1,4 @@
+Improved placing of simple query windows in Tkinter (such as
+:func:`tkinter.simpledialog.askinteger`). They are now centered at the
+center of the parent window if it is specified and shown, otherwise at the
+center of the screen.