gh-152638: Import warnings locally and use semantic line breaks

Import warnings inside askopenfiles() rather than at module level, since
it is only used by the deprecation there.  Break the new documentation
lines at sentence and clause boundaries.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: serhiy-storchaka

Doc/library/dialog.rst

@@ -164,21 +164,21 @@ string, an empty tuple, an empty list or ``None``.
 
 .. function:: askopenfile(mode="r", **options)
 
-   Create an :class:`Open` dialog and return the opened file object, or
-   ``None`` if the dialog is cancelled.
+   Create an :class:`Open` dialog and return the opened file object,
+   or ``None`` if the dialog is cancelled.
    The file is opened in mode *mode* (read-only ``'r'`` by default).
 
 .. function:: askopenfiles(mode="r", **options)
 
-   Create an :class:`Open` dialog and return a list of the opened file
-   objects, or an empty list if cancelled.
+   Create an :class:`Open` dialog and return a list of the opened file objects,
+   or an empty list if cancelled.
    The files are opened in mode *mode* (read-only ``'r'`` by default).
 
    .. deprecated-removed:: next 3.19
-      Opening several files at once is error-prone, and the returned list
-      cannot be used in a :keyword:`with` statement.
-      Iterate over the names returned by :func:`askopenfilenames` and open
-      them one by one instead.
+      Opening several files at once is error-prone,
+      and the returned list cannot be used in a :keyword:`with` statement.
+      Iterate over the names returned by :func:`askopenfilenames`
+      and open them one by one instead.
 
 .. function:: asksaveasfile(mode="w", **options)
 

Lib/tkinter/filedialog.py

@@ -19,7 +19,6 @@
 import fnmatch
 import os
 import tkinter
-import warnings
 from tkinter import (
     ACTIVE, CENTER, EW, NORMAL, NS, NSEW, RAISED, W, YES, BOTTOM, TOP, Tk, X,
     Toplevel, END, Listbox, BOTH,
@@ -576,6 +575,7 @@ def askopenfiles(mode = "r", **options):
     returns a list of open file objects or an empty list if
     cancel selected
     """
+    import warnings
     warnings._deprecated(
         "tkinter.filedialog.askopenfiles",
         message=f"{warnings._DEPRECATED_MSG}; iterate over the names returned "