Document the new formatter behaviour, skip relevant test on 3.14+

krassowski · krassowski · commit df1115803aaa · 2025-08-25T14:49:34.000+01:00
diff --git a/IPython/utils/text.py b/IPython/utils/text.py
@@ -439,6 +439,10 @@ class EvalFormatter(Formatter):
     standard string formatting), so if slicing is required, you must explicitly
     create a slice.
 
+    Note that on Python 3.14+ this version interprets `[]` as indexing operator
+    so you need to use generators instead of list comprehensions, for example:
+    `list(i for i in range(10))`.
+
     This is to be used in templating cases, such as the parallel batch
     script templates, where simple arithmetic on arguments is useful.
 
diff --git a/tests/test_text.py b/tests/test_text.py
@@ -13,6 +13,7 @@
 # -----------------------------------------------------------------------------
 
 import os
+import sys
 import math
 import random
 
@@ -27,13 +28,19 @@
 # -----------------------------------------------------------------------------
 
 
+def eval_formatter_list_comprehension_check(f):
+    ns = dict(n=12)
+    s = f.format("{[n//i for i in range(1,8)]}", **ns)
+    assert s == "[12, 6, 4, 3, 2, 2, 1]"
+
+
 def eval_formatter_check(f):
     ns = dict(n=12, pi=math.pi, stuff="hello there", os=os, u="café", b="café")
     s = f.format("{n} {n//4} {stuff.split()[0]}", **ns)
     assert s == "12 3 hello"
     s = f.format(" ".join(["{n//%i}" % i for i in range(1, 8)]), **ns)
     assert s == "12 6 4 3 2 2 1"
-    s = f.format("{[n//i for i in range(1,8)]}", **ns)
+    s = f.format("{list(n//i for i in range(1,8))}", **ns)
     assert s == "[12, 6, 4, 3, 2, 2, 1]"
     s = f.format("{stuff!s}", **ns)
     assert s == ns["stuff"]
@@ -78,12 +85,15 @@ def test_eval_formatter():
     f = text.EvalFormatter()
     eval_formatter_check(f)
     eval_formatter_no_slicing_check(f)
+    if sys.version_info < (3, 14):
+        eval_formatter_list_comprehension_check(f)
 
 
 def test_full_eval_formatter():
     f = text.FullEvalFormatter()
     eval_formatter_check(f)
     eval_formatter_slicing_check(f)
+    eval_formatter_list_comprehension_check(f)
 
 
 def test_dollar_formatter():
