python · AA-Turner · Jun 6, 2025
diff --git a/Doc/library/string.rst b/Doc/library/string.rst
@@ -264,6 +264,8 @@ Some simple format string examples::
    "Weight in tons {0.weight}"       # 'weight' attribute of first positional arg
    "Units destroyed: {players[0]}"   # First element of keyword argument 'players'.
 
+.. _formatstrings-conversion:
+
 The *conversion* field causes a type coercion before formatting.  Normally, the
 job of formatting a value is done by the :meth:`~object.__format__` method of the value
 itself.  However, in some cases it is desirable to force a type to be formatted

@@ -0,0 +1,46 @@
+:mod:`!string.templatelib` --- Support for template string literals
+===================================================================
+
+.. module:: string.templatelib
+   :synopsis: Support for template string literals.
+
+**Source code:** :source:`Lib/string/templatelib.py`
+
+--------------
+
+.. versionadded:: 3.14
+
+.. seealso::
+
+   :pep:`750` -- Template Strings
+
+Types
+-----
+
+.. class:: Template
+
+.. class:: Interpolation
+
+Helper functions
+----------------
+
+.. function:: convert(obj, /, conversion)
+
+   Applies formatted string literal :ref:`conversion <formatstrings-conversion>`
+   semantics to the given object *obj*.
+   This is frequently useful for custom template string processing logic.
+
+   Three conversion flags are currently supported:
+
+   * ``'!s'`` which calls :func:`str` on the value,
+   * ``'!r'`` which calls :func:`repr`, and
+   * ``'!a'`` which calls :func:`ascii`.
+
+   If the conversion flag is ``None``, *obj* is returned unchanged.
+
+.. _template-strings:
+
+Template String Syntax
+----------------------
+
+.. TODO: Add section similar to :ref:`formatstrings`.
diff --git a/Doc/library/text.rst b/Doc/library/text.rst
@@ -16,6 +16,7 @@ Python's built-in string type in :ref:`textseq`.
 .. toctree::
 
    string.rst
+   string.templatelib.rst
    re.rst
    difflib.rst
    textwrap.rst

@@ -1,15 +1,22 @@
 """Support for template string literals (t-strings)."""
 
-__all__ = [
-    "Interpolation",
-    "Template",
-]
-
 t = t"{0}"
 Template = type(t)
 Interpolation = type(t.interpolations[0])
 del t
 
+def convert(obj, /, conversion):
+    """Implements formatted string literals conversion semantics."""
+    if conversion is None:
+        return obj
+    if conversion == 'r':
+        return repr(obj)
+    if conversion == 's':
+        return str(obj)
+    if conversion == 'a':
+        return ascii(obj)
+    raise ValueError(f'invalid conversion specifier: {conversion!r}')
+
 def _template_unpickle(*args):
     import itertools
 

@@ -1,7 +1,7 @@
 import pickle
 import unittest
 from collections.abc import Iterator, Iterable
-from string.templatelib import Template, Interpolation
+from string.templatelib import Template, Interpolation, convert
 
 from test.test_string._support import TStringBaseCase, fstring
 
@@ -156,5 +156,23 @@ def test_exhausted(self):
         self.assertRaises(StopIteration, next, template_iter)
 
 
+class TestFunctions(unittest.TestCase):
+    def test_convert(self):
+        for obj in ('Café', None, 3.14, b'bytes'):
+            with self.subTest(f'{obj=}'):
+                self.assertEqual(convert(obj, None), obj)
+                self.assertEqual(convert(obj, 's'), str(obj))
+                self.assertEqual(convert(obj, 'r'), repr(obj))
+                self.assertEqual(convert(obj, 'a'), ascii(obj))
+
+                # Invalid conversion specifier
+                with self.assertRaises(ValueError):
+                    convert(obj, 'z')
+                with self.assertRaises(ValueError):
+                    convert(obj, 1)
+                with self.assertRaises(ValueError):
+                    convert(obj, object())
+
+
 if __name__ == '__main__':
     unittest.main()