SyntaxWarning for an invalid index type calls a t-string a str

Bug report

Bug description:

When a t-string is used as an index, the SyntaxWarning calls it a str. The warning reports the correct type for other types of invalid expression in that context. The TypeError also reports the correct type.

>>> [][t""]
<python-input-0>:1: SyntaxWarning: list indices must be integers or slices, not str; perhaps you missed a comma?
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    [][t""]
    ~~^^^^^
TypeError: list indices must be integers or slices, not string.templatelib.Template

CPython versions tested on:

3.14

Operating systems tested on:

macOS

Linked PRs

@lysnikolaou

This patch would be a possible fix:

diff --git a/Python/codegen.c b/Python/codegen.c
index 53388592330..0b8fb42376c 100644
--- a/Python/codegen.c
+++ b/Python/codegen.c
@@ -29,6 +29,7 @@
 #include "pycore_symtable.h"      // PySTEntryObject
 #include "pycore_unicodeobject.h" // _PyUnicode_EqualToASCIIString
 #include "pycore_ceval.h"         // SPECIAL___ENTER__
+#include "pycore_template.h"
 
 #define NEED_OPCODE_METADATA
 #include "pycore_opcode_metadata.h" // _PyOpcode_opcode_metadata, _PyOpcode_num_popped/pushed
@@ -3617,10 +3618,11 @@ infer_type(expr_ty e)
         return &PyGen_Type;
     case Lambda_kind:
         return &PyFunction_Type;
-    case JoinedStr_kind:
     case TemplateStr_kind:
-    case FormattedValue_kind:
     case Interpolation_kind:
+        return &_PyTemplate_Type;
+    case JoinedStr_kind:
+    case FormattedValue_kind:
         return &PyUnicode_Type;
     case Constant_kind:
         return Py_TYPE(e->v.Constant.value);

$ ./python -c '[][t""]'
<string>:1: SyntaxWarning: list indices must be integers or slices, not string.templatelib.Template; perhaps you missed a comma?
Traceback (most recent call last):
  File "<string>", line 1, in <module>
    [][t""]
    ~~^^^^^
TypeError: list indices must be integers or slices, not string.templatelib.Template

But I wonder if there's a reason it wasn't done this way in the first place?

cc @lysnikolaou

Another related case:

>>> [t"x" [1, 2]]
<python-input-5>:1: SyntaxWarning: str indices must be integers or slices, not tuple; perhaps you missed a comma?
Traceback (most recent call last):
  File "<python-input-5>", line 1, in <module>
    [t"x" [1, 2]]
     ~~~~~^^^^^^
TypeError: 'string.templatelib.Template' object is not subscriptable

Ideally, the SyntaxWarning should say that Template objects aren't subscriptable, similar to what's done for e.g. sets:

>>> [{1} [1, 2]]
<python-input-6>:1: SyntaxWarning: 'set' object is not subscriptable; perhaps you missed a comma?
Traceback (most recent call last):
  File "<python-input-6>", line 1, in <module>
    [{1} [1, 2]]
     ~~~~^^^^^^
TypeError: 'set' object is not subscriptable

gh-138372: Fix SyntaxWarning for erroneous t-string subscription (#13…

pythongh-138372: Fix SyntaxWarning for erroneous t-string subscription (

@brianschubert

Thanks a lot @brianschubert!

[3.14] gh-138372: Fix SyntaxWarning for erroneous t-string subscripti…

@dscorbett

Backport has been merged. Thanks for the report @dscorbett!

[3.14] pythongh-138372: Fix SyntaxWarning for erroneous t-string subs…

pythongh-138372: Fix SyntaxWarning for erroneous t-string subscription (

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`SyntaxWarning` for an invalid index type calls a t-string a `str` #138372

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SyntaxWarning for an invalid index type calls a t-string a str #138372

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Bug description:

CPython versions tested on:

Operating systems tested on:

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brianschubert commented on Sep 2, 2025

brianschubert commented on Sep 2, 2025

pablogsal commented on Sep 2, 2025

brianschubert commented on Sep 2, 2025

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`SyntaxWarning` for an invalid index type calls a t-string a `str` #138372