gh-151099: Better repr output for template strings.

Author: doerwalter

Lib/test/test_string/test_templatelib.py

@@ -101,6 +101,25 @@ def test_template_values(self):
         t = t'Hello, {name}, {age} from {country}'
         self.assertEqual(t.values, ("Lys", 0, "GR"))
 
+    def test_repr(self):
+        self.assertEqual(repr(t''), 'Template()')
+        self.assertEqual(repr(t'foo'), "Template('foo')")
+        x = 42
+        self.assertEqual(
+            repr(t'{x}'),
+            "Template(Interpolation(42, 'x', None, ''))")
+        self.assertEqual(
+            repr(t'a{x!r:02}b'),
+            "Template('a', Interpolation(42, 'x', 'r', '02'), 'b')")
+
+        # Test a "recursive" template
+        x = []
+        t = t'a{x}b'
+        x.append(t)
+        self.assertEqual(
+            repr(t),
+            "Template('a', Interpolation([Template(...)], 'x', None, ''), 'b')")
+
     def test_pickle_template(self):
         user = 'test'
         for template in (

Misc/NEWS.d/next/Library/2026-06-08-20-38-28.gh-issue-151099.6Opls1.rst

@@ -0,0 +1,2 @@
+Change :func:`repr` output of :class:`string.templatelib.Template` objects
+to list the parts of the template in their original source order.

Objects/templateobject.c

@@ -212,10 +212,70 @@ static PyObject *
 template_repr(PyObject *op)
 {
     templateobject *self = templateobject_CAST(op);
-    return PyUnicode_FromFormat("%s(strings=%R, interpolations=%R)",
-                                _PyType_Name(Py_TYPE(self)),
-                                self->strings,
-                                self->interpolations);
+
+    int res = Py_ReprEnter(self);
+    if (res != 0) {
+        return (res > 0 ? PyUnicode_FromString("Template(...)") : NULL);
+    }
+
+    Py_ssize_t stringslen = PyTuple_GET_SIZE(self->strings);
+    Py_ssize_t interpolationslen = PyTuple_GET_SIZE(self->interpolations);
+
+    PyUnicodeWriter *writer = PyUnicodeWriter_Create(10);
+    if (writer == NULL) {
+        return NULL;
+    }
+
+    if (PyUnicodeWriter_WriteUTF8(writer, _PyType_Name(Py_TYPE(self)), -1) < 0) {
+        goto error;
+    }
+    if (PyUnicodeWriter_WriteChar(writer, '(') < 0) {
+        goto error;
+    }
+
+    /* Render the strings and interpolations in the order they appeared in the
+       constructor call, i.e. interleaved and skipping empty strings. This
+       matches the order produced by templateiter_next. */
+    int first = 1;
+    for (Py_ssize_t i = 0; i < stringslen; i++) {
+        PyObject *string = PyTuple_GET_ITEM(self->strings, i);
+        if (PyUnicode_GET_LENGTH(string) > 0) {
+            if (!first) {
+                if (PyUnicodeWriter_WriteASCII(writer, ", ", 2) < 0) {
+                    goto error;
+                }
+            }
+            if (PyUnicodeWriter_WriteRepr(writer, string) < 0) {
+                goto error;
+            }
+            first = 0;
+        }
+        if (i < interpolationslen) {
+            PyObject *interpolation = PyTuple_GET_ITEM(self->interpolations, i);
+            if (!first) {
+                if (PyUnicodeWriter_WriteASCII(writer, ", ", 2) < 0) {
+                    goto error;
+                }
+            }
+            if (PyUnicodeWriter_WriteRepr(writer, interpolation) < 0) {
+                goto error;
+            }
+            first = 0;
+        }
+    }
+
+    if (PyUnicodeWriter_WriteChar(writer, ')') < 0) {
+        goto error;
+    }
+
+    Py_ReprLeave(self);
+
+    return PyUnicodeWriter_Finish(writer);
+
+error:
+    Py_ReprLeave(self);
+    PyUnicodeWriter_Discard(writer);
+    return NULL;
 }
 
 static PyObject *