FEATURE: History: allow session number without trailing slash

Carreau · Carreau · commit 83d61110828d · 2025-11-28T20:35:41.000+01:00
Prompted by #15069
diff --git a/IPython/core/history.py b/IPython/core/history.py
@@ -1148,13 +1148,15 @@ def __del__(self) -> None:
         self.stop()
 
 
-# To match, e.g. ~5/8-~2/3
+# To match, e.g. ~5/8-~2/3, or ~4 (without trailing slash for full session)
+# Session numbers: ~N or N/
+# Line numbers: N (just digits, no ~ and no /)
 range_re = re.compile(
     r"""
-((?P<startsess>~?\d+)/)?
+((?P<startsess>(?:~\d+/?|\d+/)))?
 (?P<start>\d+)?
 ((?P<sep>[\-:])
- ((?P<endsess>~?\d+)/)?
+ ((?P<endsess>(?:~\d+/?|\d+/)))?
  (?P<end>\d+))?
 $""",
     re.VERBOSE,
@@ -1171,6 +1173,8 @@ def extract_hist_ranges(ranges_str: str) -> Iterable[tuple[int, int, Optional[in
     --------
     >>> list(extract_hist_ranges("~8/5-~7/4 2"))
     [(-8, 5, None), (-7, 1, 5), (0, 2, 3)]
+    >>> list(extract_hist_ranges("~4"))
+    [(-4, 1, None)]  # Full session 4 (trailing / is optional)
     """
     if ranges_str == "":
         yield (0, 1, None)  # Everything from current session
@@ -1197,6 +1201,9 @@ def extract_hist_ranges(ranges_str: str) -> Iterable[tuple[int, int, Optional[in
             end += 1
         startsess = rmatch.group("startsess") or "0"
         endsess = rmatch.group("endsess") or startsess
+        # Strip trailing / from session numbers (e.g., "~4/" -> "~4", "4/" -> "4")
+        startsess = startsess.rstrip("/")
+        endsess = endsess.rstrip("/")
         startsess = int(startsess.replace("~", "-"))
         endsess = int(endsess.replace("~", "-"))
         assert endsess >= startsess, "start session must be earlier than end session"
diff --git a/IPython/core/magics/history.py b/IPython/core/magics/history.py
@@ -121,10 +121,12 @@ def history(self, parameter_s = ''):
             Line 4, current session
         ``4-6``
             Lines 4-6, current session
-        ``~2/``
+        ``~2/`` or `~2`
             All lines of session 2 before current
         ``243/1-5``
             Lines 1-5, session 243
+        ``~2/7``
+            Line 7, session 2 before current
         ``~8/1-~6/5``
             From the first line of 8 sessions ago, to the fifth line of 6
             sessions ago.
diff --git a/tests/test_history.py b/tests/test_history.py
@@ -209,6 +209,44 @@ def test_extract_hist_ranges_empty_str():
     assert actual == expected
 
 
+@pytest.mark.parametrize(
+    "instr,expected,description",
+    [
+        ("~4/", [(-4, 1, None)], "with trailing slash"),
+        ("~4", [(-4, 1, None)], "without trailing slash"),
+        ("~4/1-5", [(-4, 1, 6)], "with line ranges and trailing slash"),
+        (
+            "~4 ~5/ ~6/1-3",
+            [(-4, 1, None), (-5, 1, None), (-6, 1, 4)],
+            "multiple sessions with mixed syntax",
+        ),
+        ("~10 ~20/", [(-10, 1, None), (-20, 1, None)], "larger session numbers"),
+        ("~1", [(-1, 1, None)], "single digit session without slash"),
+        ("~1/", [(-1, 1, None)], "single digit session with slash"),
+        ("~2", [(-2, 1, None)], "backward compatibility without slash"),
+        ("~2/", [(-2, 1, None)], "backward compatibility with slash"),
+    ],
+)
+def test_extract_hist_ranges_without_trailing_slash(instr, expected, description):
+    """Test that ~N (without trailing slash) works and is backward compatible with ~N/"""
+    actual = list(extract_hist_ranges(instr))
+    assert (
+        actual == expected
+    ), f"Failed for '{instr}' ({description}): expected {expected}, got {actual}"
+
+
+def test_extract_hist_ranges_backward_compatibility():
+    """Test that ~N and ~N/ produce identical results (backward compatibility)"""
+    test_cases = ["~4", "~5", "~10", "~20"]
+    for case in test_cases:
+        result_no_slash = list(extract_hist_ranges(case))
+        result_with_slash = list(extract_hist_ranges(case + "/"))
+        assert result_no_slash == result_with_slash, (
+            f"{case} and {case}/ should produce the same result, "
+            f"got {result_no_slash} vs {result_with_slash}"
+        )
+
+
 def test_magic_rerun():
     """Simple test for %rerun (no args -> rerun last line)"""
     ip = get_ipython()
