python · tanloong · Mar 1, 2026 · Mar 1, 2026
@@ -41,11 +41,11 @@ def prefix(wordlist: list[str], j: int = 0) -> str:
            for word in wordlist:
                d[word[i]] = 1
            if len(d) > 1:
-                return wordlist[0][j:i]
+                return wordlist[0][:i]
            i += 1
            d = {}
    except IndexError:
-        return wordlist[0][j:i]
+        return wordlist[0][:i]
    return ""


@@ -181,10 +181,16 @@ def do(self) -> None:
            if completions_unchangable and len(completions[0]) == len(stem):
                r.msg = "[ sole completion ]"
                r.dirty = True
-            r.insert(completions[0][len(stem):])
+            stem_len = len(stem)
+            del r.buffer[r.pos - stem_len:r.pos]
+            r.pos -= stem_len
+            r.insert(completions[0])
        else:
            p = prefix(completions, len(stem))
            if p:
+                stem_len = len(stem)
+                del r.buffer[r.pos - stem_len:r.pos]
+                r.pos -= stem_len
                r.insert(p)
            if last_is_completer:
                r.cmpltn_menu_visible = True

@@ -936,6 +936,25 @@ def test_func(self):
        self.assertEqual(output, "dummy.test_func.__")
        self.assertEqual(mock_stderr.getvalue(), "")

+    def test_completion_replaces_input(self):
+        matches = []
+        def case_insensitive_completer(text, state):
+            nonlocal matches
+            candidates = ["PYTHON", "PYREPL"]
+            if state == 0:
+                matches = [c for c in candidates if c.lower().startswith(text.lower())]
+            if state < len(matches):
+                return matches[state]
+            return None
+
+        events = code_to_events("s='pyt\t'\ns='py\t\tr\t'\n")
+        reader = self.prepare_reader(events, {})
+        reader.config.readline_completer = case_insensitive_completer
+        output = multiline_input(reader)
+        self.assertEqual(output, "s='PYTHON'")
+
+        output = multiline_input(reader)
+        self.assertEqual(output, "s='PYREPL'")

 class TestPyReplModuleCompleter(TestCase):
    def setUp(self):

diff --git a/Misc/NEWS.d/next/Library/2026-03-01-23-27-19.gh-issue-145392.uiNk5Y.rst b/Misc/NEWS.d/next/Library/2026-03-01-23-27-19.gh-issue-145392.uiNk5Y.rst
@@ -0,0 +1 @@
+Fix :mod:`!_pyrepl` completion to replace input stem instead of appending.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Fix :mod:`!_pyrepl` completion to replace input stem instead of appending.