Use vi-specific backward word logic

Use vi_backward_word on b key in vi mode as the original emacs mode
implementation respects different word boundaries.

Author: lkollar

Lib/_pyrepl/reader.py

@@ -157,7 +157,7 @@ def make_default_commands() -> dict[CommandName, type[Command]]:
         (r"0", "beginning-of-line"),
         (r"$", "end-of-line"),
         (r"w", "vi-forward-word"),
-        (r"b", "backward-word"),
+        (r"b", "vi-backward-word"),
         (r"e", "end-of-word"),
         (r"^", "first-non-whitespace-character"),
 

Lib/_pyrepl/vi_commands.py

@@ -28,6 +28,13 @@ def do(self) -> None:
             r.pos = r.vi_forward_word()
 
 
+class vi_backward_word(MotionCommand):
+    def do(self) -> None:
+        r = self.reader
+        for _ in range(r.get_arg()):
+            r.pos = r.vi_bow()
+
+
 # ============================================================================
 # Mode Switching Commands
 # ============================================================================

Lib/test/test_pyrepl/test_reader.py

@@ -1011,6 +1011,16 @@ def test_vi_word_boundaries(self):
             ("foo.bar", "0e", 2, "e lands on last o of foo"),
             ("foo.bar", "0ee", 3, "second e lands on dot"),
             ("foo.bar", "0eee", 6, "third e lands on last r of bar"),
+
+            # Backward word (b) - cursor at end after ESC
+            ("foo bar", "$b", 4, "b from end lands on bar"),
+            ("foo bar", "$bb", 0, "two b's lands on foo"),
+            ("foo.bar", "$b", 4, "b from end lands on bar"),
+            ("foo.bar", "$bb", 3, "second b lands on dot"),
+            ("foo.bar", "$bbb", 0, "third b lands on foo"),
+            ("get_value(x)", "$b", 10, "b from end lands on x"),
+            ("get_value(x)", "$bb", 9, "second b lands on ("),
+            ("get_value(x)", "$bbb", 0, "third b lands on get_value"),
         ]
 
         for text, keys, expected_pos, desc in test_cases: