[3.13] gh-103878: Document that the cancelled file dialog value is only falsy (GH...

Its exact type (empty string, tuple, list or None) varies between
platforms and Tk versions, so advise testing the result for truth.
(cherry picked from commit 9dd3340a623093b5d0ff054d5d42c370bb09221c)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

diff --git a/Doc/library/dialog.rst b/Doc/library/dialog.rst
index f24b9f84b1e44b7acb0c76a101b2e6bd3e4a8d2f..06fecc912efa5d68517ad2f8c34f9e302266f410 100644 (file)
--- a/Doc/library/dialog.rst
+++ b/Doc/library/dialog.rst
@@ -131,7 +131,10 @@ 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, an empty list or ``None``.
+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.
 
 .. function:: askopenfile(mode="r", **options)
               askopenfiles(mode="r", **options)
@@ -140,7 +143,7 @@ cancelled it is an empty string, an empty tuple, an empty list or ``None``.
    :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
-   list if cancelled.
+   tuple if cancelled.
    The files are opened in mode *mode* (read-only ``'r'`` by default).
 
 .. function:: asksaveasfile(mode="w", **options)