gh-38066: Add Shift-Tab smart-dedent in IDLE editor

Lib/idlelib/config-keys.def

@@ -47,6 +47,7 @@ goto-line=<Alt-Key-g> <Meta-Key-g> <Alt-Key-G> <Meta-Key-G>
 smart-backspace=<Key-BackSpace>
 newline-and-indent=<Key-Return> <Key-KP_Enter>
 smart-indent=<Key-Tab>
+smart-dedent=<Shift-Key-Tab>
 indent-region=<Control-Key-bracketright>
 dedent-region=<Control-Key-bracketleft>
 comment-region=<Alt-Key-3> <Meta-Key-3>
@@ -107,6 +108,7 @@ goto-line=<Alt-Key-g> <Meta-Key-g>
 smart-backspace=<Key-BackSpace>
 newline-and-indent=<Key-Return> <Key-KP_Enter>
 smart-indent=<Key-Tab>
+smart-dedent=<Shift-Key-Tab>
 indent-region=<Control-Key-bracketright>
 dedent-region=<Control-Key-bracketleft>
 comment-region=<Alt-Key-3>
@@ -167,6 +169,7 @@ goto-line = <Control-Key-g>
 smart-backspace = <Key-BackSpace>
 newline-and-indent = <Key-Return> <Key-KP_Enter>
 smart-indent = <Key-Tab>
+smart-dedent = <Shift-Key-Tab>
 indent-region = <Control-Key-bracketright>
 dedent-region = <Control-Key-bracketleft>
 comment-region = <Control-Key-d>
@@ -227,6 +230,7 @@ goto-line=<Command-Key-j>
 smart-backspace=<Key-BackSpace>
 newline-and-indent=<Key-Return> <Key-KP_Enter>
 smart-indent=<Key-Tab>
+smart-dedent=<Shift-Key-Tab>
 indent-region=<Command-Key-bracketright>
 dedent-region=<Command-Key-bracketleft>
 comment-region=<Control-Key-3>
@@ -275,6 +279,7 @@ smart-backspace = <Key-BackSpace>
 change-indentwidth = <Control-Key-u>
 do-nothing = <Control-Key-F12>
 smart-indent = <Key-Tab>
+smart-dedent = <Shift-Key-Tab>
 center-insert = <Control-Key-l>
 history-next = <Control-Key-n>
 del-word-right = <Option-Key-Delete>

Lib/idlelib/config.py

@@ -678,6 +678,7 @@ def GetCoreKeys(self, keySetName=None):
             '<<smart-backspace>>': ['<Key-BackSpace>'],
             '<<newline-and-indent>>': ['<Key-Return>', '<Key-KP_Enter>'],
             '<<smart-indent>>': ['<Key-Tab>'],
+            '<<smart-dedent>>': ['<Shift-Key-Tab>', '<Shift-ISO_Left_Tab>'],
             '<<indent-region>>': ['<Control-Key-bracketright>'],
             '<<dedent-region>>': ['<Control-Key-bracketleft>'],
             '<<comment-region>>': ['<Alt-Key-3>'],

Lib/idlelib/editor.py

@@ -141,6 +141,7 @@ def __init__(self, flist=None, filename=None, key=None, root=None):
         text.bind("<<smart-backspace>>",self.smart_backspace_event)
         text.bind("<<newline-and-indent>>",self.newline_and_indent_event)
         text.bind("<<smart-indent>>",self.smart_indent_event)
+        text.bind("<<smart-dedent>>", self.smart_dedent_event)
         self.fregion = fregion = self.FormatRegion(self)
         # self.fregion used in smart_indent_event to access indent_region.
         text.bind("<<indent-region>>", fregion.indent_region_event)
@@ -1426,6 +1427,23 @@ def smart_indent_event(self, event):
         finally:
             text.undo_block_stop()
 
+    def smart_dedent_event(self, event):
+        text = self.text
+        first, last = self.get_selection_indices()
+        text.undo_block_start()
+        try:
+            if first and last:
+                if index2line(first) != index2line(last):
+                    return self.fregion.dedent_region_event(event)
+            prefix = text.get("insert linestart", "insert")
+            raw, effective = get_line_indent(prefix, self.tabwidth)
+            if raw == len(prefix) and effective > 0:
+                self.reindent_to(max(0, effective - self.indentwidth))
+            text.see("insert")
+            return "break"
+        finally:
+            text.undo_block_stop()
+
     def newline_and_indent_event(self, event):
         """Insert a newline and indentation after Enter keypress event.
 

Misc/NEWS.d/next/IDLE/2026-10-28-01-38-00.gh-issue-38066.idle-dedent.rst

@@ -0,0 +1 @@
+Add smart-dedent bound to Shift-Tab in IDLE to dedent selected lines or the current line.