gh-103878: Return a consistent empty value from cancelled file dialogs

Doc/library/dialog.rst

@@ -159,10 +159,8 @@ listed below:
 The below functions when called create a modal, native look-and-feel dialog,
 wait for the user's selection, and return it.
 The exact return value depends on the function (see below); when the dialog is
-cancelled it is an empty string, an empty tuple or ``None``.
-The precise type of this empty value may vary between platforms and Tk
-versions, so test the result for truth rather than comparing it with a
-specific value.
+cancelled it is the empty value documented for that function -- an empty
+string, an empty tuple, an empty list or ``None``.
 
 .. function:: askopenfile(mode="r", **options)
               askopenfiles(mode="r", **options)
@@ -171,7 +169,7 @@ specific value.
    :func:`askopenfile` returns the opened file object, or ``None`` if the
    dialog is cancelled.
    :func:`askopenfiles` returns a list of the opened file objects, or an empty
-   tuple if cancelled.
+   list if cancelled.
    The files are opened in mode *mode* (read-only ``'r'`` by default).
 
 .. function:: asksaveasfile(mode="w", **options)

Lib/test/test_tkinter/test_filedialog.py

@@ -37,6 +37,39 @@ def test_directory(self):
         self.check(filedialog.Directory, 'tk_chooseDirectory')
 
 
+class CancelResultTest(AbstractTkTest, unittest.TestCase):
+    # On cancellation Tcl may report the empty result as '', () or b''
+    # (gh-103878).  _fixresult() normalizes it to the documented empty value:
+    # '' for the filename dialogs and () for the multiple-selection dialog.
+
+    def check(self, dialog, expected):
+        for empty in ('', (), b''):
+            with self.subTest(empty=empty):
+                result = dialog._fixresult(self.root, empty)
+                self.assertEqual(result, expected)
+                self.assertIs(type(result), type(expected))
+
+    def test_open(self):
+        self.check(filedialog.Open(self.root), '')
+
+    def test_saveas(self):
+        self.check(filedialog.SaveAs(self.root), '')
+
+    def test_directory(self):
+        self.check(filedialog.Directory(self.root), '')
+
+    def test_openfilenames(self):
+        self.check(filedialog.Open(self.root, multiple=1), ())
+
+    def test_results_preserved(self):
+        # A real selection is returned unchanged.
+        single = filedialog.Open(self.root)
+        self.assertEqual(single._fixresult(self.root, '/a/spam'), '/a/spam')
+        multiple = filedialog.Open(self.root, multiple=1)
+        self.assertEqual(multiple._fixresult(self.root, ('/a', '/b')),
+                         ('/a', '/b'))
+
+
 class FileDialogTest(AbstractTkTest, unittest.TestCase):
     # The pure-Python FileDialog runs its own modal loop in go(); its logic is
     # exercised here without entering the loop.

Lib/tkinter/filedialog.py

@@ -311,7 +311,9 @@ def _fixoptions(self):
             pass
 
     def _fixresult(self, widget, result):
-        if result:
+        if not result:
+            result = ''  # normalize the cancelled result (gh-103878)
+        else:
             # keep directory and filename until next time
             # convert Tcl path objects to strings
             try:
@@ -335,17 +337,16 @@ class Open(_Dialog):
     command = "tk_getOpenFile"
 
     def _fixresult(self, widget, result):
-        if isinstance(result, tuple):
-            # multiple results:
+        if self.options.get("multiple"):
+            # multiple results: a tuple of filenames
+            if not isinstance(result, tuple):
+                result = widget.tk.splitlist(result)
             result = tuple([getattr(r, "string", r) for r in result])
             if result:
                 path, file = os.path.split(result[0])
                 self.options["initialdir"] = path
                 # don't set initialfile or filename, as we have multiple of these
             return result
-        if not widget.tk.wantobjects() and "multiple" in self.options:
-            # Need to split result explicitly
-            return self._fixresult(widget, widget.tk.splitlist(result))
         return _Dialog._fixresult(self, widget, result)
 
 
@@ -362,7 +363,9 @@ class Directory(commondialog.Dialog):
     command = "tk_chooseDirectory"
 
     def _fixresult(self, widget, result):
-        if result:
+        if not result:
+            result = ''  # normalize the cancelled result (gh-103878)
+        else:
             # convert Tcl path objects to strings
             try:
                 result = result.string
@@ -420,12 +423,7 @@ def askopenfiles(mode = "r", **options):
     """
 
     files = askopenfilenames(**options)
-    if files:
-        ofiles=[]
-        for filename in files:
-            ofiles.append(open(filename, mode))
-        files=ofiles
-    return files
+    return [open(filename, mode) for filename in files]
 
 
 def asksaveasfile(mode = "w", **options):

Misc/NEWS.d/next/Library/2026-06-27-19-02-17.gh-issue-103878.216fa7.rst

@@ -0,0 +1,8 @@
+The :mod:`tkinter.filedialog` functions that return a filename
+(:func:`~tkinter.filedialog.askopenfilename`,
+:func:`~tkinter.filedialog.asksaveasfilename` and
+:func:`~tkinter.filedialog.askdirectory`) now consistently return an empty
+string when the dialog is cancelled, instead of an empty tuple or ``b''``
+on some platforms.  :func:`~tkinter.filedialog.askopenfilenames` likewise
+always returns an empty tuple, and :func:`~tkinter.filedialog.askopenfiles`
+an empty list.