RustPython · youknowone · Feb 1, 2026 · Feb 1, 2026 · Feb 1, 2026 · Feb 1, 2026
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
@@ -101,6 +101,7 @@ env:
     test_subclassinit
     test_super
     test_syntax
+    test_tstring
     test_tuple
     test_types
     test_unary

diff --git a/Lib/test/test_tstring.py b/Lib/test/test_tstring.py
@@ -0,0 +1,296 @@
+import unittest
+
+from test.test_string._support import TStringBaseCase, fstring
+
+
+class TestTString(unittest.TestCase, TStringBaseCase):
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; + Template(strings=('Hello',), interpolations=())
+    def test_string_representation(self):
+        # Test __repr__
+        t = t"Hello"
+        self.assertEqual(repr(t), "Template(strings=('Hello',), interpolations=())")
+
+        name = "Python"
+        t = t"Hello, {name}"
+        self.assertEqual(repr(t),
+            "Template(strings=('Hello, ', ''), "
+            "interpolations=(Interpolation('Python', 'name', None, ''),))"
+        )
+
+    def test_interpolation_basics(self):
+        # Test basic interpolation
+        name = "Python"
+        t = t"Hello, {name}"
+        self.assertTStringEqual(t, ("Hello, ", ""), [(name, "name")])
+        self.assertEqual(fstring(t), "Hello, Python")
+
+        # Multiple interpolations
+        first = "Python"
+        last = "Developer"
+        t = t"{first} {last}"
+        self.assertTStringEqual(
+            t, ("", " ", ""), [(first, 'first'), (last, 'last')]
+        )
+        self.assertEqual(fstring(t), "Python Developer")
+
+        # Interpolation with expressions
+        a = 10
+        b = 20
+        t = t"Sum: {a + b}"
+        self.assertTStringEqual(t, ("Sum: ", ""), [(a + b, "a + b")])
+        self.assertEqual(fstring(t), "Sum: 30")
+
+        # Interpolation with function
+        def square(x):
+            return x * x
+        t = t"Square: {square(5)}"
+        self.assertTStringEqual(
+            t, ("Square: ", ""), [(square(5), "square(5)")]
+        )
+        self.assertEqual(fstring(t), "Square: 25")
+
+        # Test attribute access in expressions
+        class Person:
+            def __init__(self, name):
+                self.name = name
+
+            def upper(self):
+                return self.name.upper()
+
+        person = Person("Alice")
+        t = t"Name: {person.name}"
+        self.assertTStringEqual(
+            t, ("Name: ", ""), [(person.name, "person.name")]
+        )
+        self.assertEqual(fstring(t), "Name: Alice")
+
+        # Test method calls
+        t = t"Name: {person.upper()}"
+        self.assertTStringEqual(
+            t, ("Name: ", ""), [(person.upper(), "person.upper()")]
+        )
+        self.assertEqual(fstring(t), "Name: ALICE")
+
+        # Test dictionary access
+        data = {"name": "Bob", "age": 30}
+        t = t"Name: {data['name']}, Age: {data['age']}"
+        self.assertTStringEqual(
+            t, ("Name: ", ", Age: ", ""),
+            [(data["name"], "data['name']"), (data["age"], "data['age']")],
+        )
+        self.assertEqual(fstring(t), "Name: Bob, Age: 30")
+
+    def test_format_specifiers(self):
+        # Test basic format specifiers
+        value = 3.14159
+        t = t"Pi: {value:.2f}"
+        self.assertTStringEqual(
+            t, ("Pi: ", ""), [(value, "value", None, ".2f")]
+        )
+        self.assertEqual(fstring(t), "Pi: 3.14")
+
+    def test_conversions(self):
+        # Test !s conversion (str)
+        obj = object()
+        t = t"Object: {obj!s}"
+        self.assertTStringEqual(t, ("Object: ", ""), [(obj, "obj", "s")])
+        self.assertEqual(fstring(t), f"Object: {str(obj)}")
+
+        # Test !r conversion (repr)
+        t = t"Data: {obj!r}"
+        self.assertTStringEqual(t, ("Data: ", ""), [(obj, "obj", "r")])
+        self.assertEqual(fstring(t), f"Data: {repr(obj)}")
+
+        # Test !a conversion (ascii)
+        text = "Café"
+        t = t"ASCII: {text!a}"
+        self.assertTStringEqual(t, ("ASCII: ", ""), [(text, "text", "a")])
+        self.assertEqual(fstring(t), f"ASCII: {ascii(text)}")
+
+        # Test !z conversion (error)
+        num = 1
+        with self.assertRaises(SyntaxError):
+            eval("t'{num!z}'")
+
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; ?          ++++++
+    def test_debug_specifier(self):
+        # Test debug specifier
+        value = 42
+        t = t"Value: {value=}"
+        self.assertTStringEqual(
+            t, ("Value: value=", ""), [(value, "value", "r")]
+        )
+        self.assertEqual(fstring(t), "Value: value=42")
+
+        # Test debug specifier with format (conversion default to !r)
+        t = t"Value: {value=:.2f}"
+        self.assertTStringEqual(
+            t, ("Value: value=", ""), [(value, "value", None, ".2f")]
+        )
+        self.assertEqual(fstring(t), "Value: value=42.00")
+
+        # Test debug specifier with conversion
+        t = t"Value: {value=!s}"
+        self.assertTStringEqual(
+            t, ("Value: value=", ""), [(value, "value", "s")]
+        )
+
+        # Test white space in debug specifier
+        t = t"Value: {value = }"
+        self.assertTStringEqual(
+            t, ("Value: value = ", ""), [(value, "value", "r")]
+        )
+        self.assertEqual(fstring(t), "Value: value = 42")
+
+    def test_raw_tstrings(self):
+        path = r"C:\Users"
+        t = rt"{path}\Documents"
+        self.assertTStringEqual(t, ("", r"\Documents"), [(path, "path")])
+        self.assertEqual(fstring(t), r"C:\Users\Documents")
+
+        # Test alternative prefix
+        t = tr"{path}\Documents"
+        self.assertTStringEqual(t, ("", r"\Documents"), [(path, "path")])
+
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; AssertionError: "can only concatenate string.templatelib.Template \(not "str"\) to string.templatelib.Template" does not match "can only concatenate Template (not 'str') to Template"
+    def test_template_concatenation(self):
+        # Test template + template
+        t1 = t"Hello, "
+        t2 = t"world"
+        combined = t1 + t2
+        self.assertTStringEqual(combined, ("Hello, world",), ())
+        self.assertEqual(fstring(combined), "Hello, world")
+
+        # Test template + string
+        t1 = t"Hello"
+        expected_msg = 'can only concatenate string.templatelib.Template ' \
+            '\\(not "str"\\) to string.templatelib.Template'
+        with self.assertRaisesRegex(TypeError, expected_msg):
+            t1 + ", world"
+
+        # Test template + template with interpolation
+        name = "Python"
+        t1 = t"Hello, "
+        t2 = t"{name}"
+        combined = t1 + t2
+        self.assertTStringEqual(combined, ("Hello, ", ""), [(name, "name")])
+        self.assertEqual(fstring(combined), "Hello, Python")
+
+        # Test string + template
+        expected_msg = 'can only concatenate str ' \
+            '\\(not "string.templatelib.Template"\\) to str'
+        with self.assertRaisesRegex(TypeError, expected_msg):
+            "Hello, " + t"{name}"
+
+    def test_nested_templates(self):
+        # Test a template inside another template expression
+        name = "Python"
+        inner = t"{name}"
+        t = t"Language: {inner}"
+
+        t_interp = t.interpolations[0]
+        self.assertEqual(t.strings, ("Language: ", ""))
+        self.assertEqual(t_interp.value.strings, ("", ""))
+        self.assertEqual(t_interp.value.interpolations[0].value, name)
+        self.assertEqual(t_interp.value.interpolations[0].expression, "name")
+        self.assertEqual(t_interp.value.interpolations[0].conversion, None)
+        self.assertEqual(t_interp.value.interpolations[0].format_spec, "")
+        self.assertEqual(t_interp.expression, "inner")
+        self.assertEqual(t_interp.conversion, None)
+        self.assertEqual(t_interp.format_spec, "")
+
+    @unittest.expectedFailure  # TODO: RUSTPYTHON multiple instances of AssertionError
+    def test_syntax_errors(self):
+        for case, err in (
+            ("t'", "unterminated t-string literal"),
+            ("t'''", "unterminated triple-quoted t-string literal"),
+            ("t''''", "unterminated triple-quoted t-string literal"),
+            ("t'{", "'{' was never closed"),
+            ("t'{'", "t-string: expecting '}'"),
+            ("t'{a'", "t-string: expecting '}'"),
+            ("t'}'", "t-string: single '}' is not allowed"),
+            ("t'{}'", "t-string: valid expression required before '}'"),
+            ("t'{=x}'", "t-string: valid expression required before '='"),
+            ("t'{!x}'", "t-string: valid expression required before '!'"),
+            ("t'{:x}'", "t-string: valid expression required before ':'"),
+            ("t'{x;y}'", "t-string: expecting '=', or '!', or ':', or '}'"),
+            ("t'{x=y}'", "t-string: expecting '!', or ':', or '}'"),
+            ("t'{x!s!}'", "t-string: expecting ':' or '}'"),
+            ("t'{x!s:'", "t-string: expecting '}', or format specs"),
+            ("t'{x!}'", "t-string: missing conversion character"),
+            ("t'{x=!}'", "t-string: missing conversion character"),
+            ("t'{x!z}'", "t-string: invalid conversion character 'z': "
+                         "expected 's', 'r', or 'a'"),
+            ("t'{lambda:1}'", "t-string: lambda expressions are not allowed "
+                              "without parentheses"),
+            ("t'{x:{;}}'", "t-string: expecting a valid expression after '{'"),
+            ("t'{1:d\n}'", "t-string: newlines are not allowed in format specifiers")
+        ):
+            with self.subTest(case), self.assertRaisesRegex(SyntaxError, err):
+                eval(case)
+
+    def test_runtime_errors(self):
+        # Test missing variables
+        with self.assertRaises(NameError):
+            eval("t'Hello, {name}'")
+
+    @unittest.expectedFailure  # TODO: RUSTPYTHON
+    def test_literal_concatenation(self):
+        # Test concatenation of t-string literals
+        t = t"Hello, " t"world"
+        self.assertTStringEqual(t, ("Hello, world",), ())
+        self.assertEqual(fstring(t), "Hello, world")
+
+        # Test concatenation with interpolation
+        name = "Python"
+        t = t"Hello, " t"{name}"
+        self.assertTStringEqual(t, ("Hello, ", ""), [(name, "name")])
+        self.assertEqual(fstring(t), "Hello, Python")
+
+        # Test disallowed mix of t-string and string/f-string (incl. bytes)
+        what = 't'
+        expected_msg = 'cannot mix t-string literals with string or bytes literals'
+        for case in (
+            "t'{what}-string literal' 'str literal'",
+            "t'{what}-string literal' u'unicode literal'",
+            "t'{what}-string literal' f'f-string literal'",
+            "t'{what}-string literal' r'raw string literal'",
+            "t'{what}-string literal' rf'raw f-string literal'",
+            "t'{what}-string literal' b'bytes literal'",
+            "t'{what}-string literal' br'raw bytes literal'",
+            "'str literal' t'{what}-string literal'",
+            "u'unicode literal' t'{what}-string literal'",
+            "f'f-string literal' t'{what}-string literal'",
+            "r'raw string literal' t'{what}-string literal'",
+            "rf'raw f-string literal' t'{what}-string literal'",
+            "b'bytes literal' t'{what}-string literal'",
+            "br'raw bytes literal' t'{what}-string literal'",
+        ):
+            with self.subTest(case):
+                with self.assertRaisesRegex(SyntaxError, expected_msg):
+                    eval(case)
+
+    def test_triple_quoted(self):
+        # Test triple-quoted t-strings
+        t = t"""
+        Hello,
+        world
+        """
+        self.assertTStringEqual(
+            t, ("\n        Hello,\n        world\n        ",), ()
+        )
+        self.assertEqual(fstring(t), "\n        Hello,\n        world\n        ")
+
+        # Test triple-quoted with interpolation
+        name = "Python"
+        t = t"""
+        Hello,
+        {name}
+        """
+        self.assertTStringEqual(
+            t, ("\n        Hello,\n        ", "\n        "), [(name, "name")]
+        )
+        self.assertEqual(fstring(t), "\n        Hello,\n        Python\n        ")
+
+if __name__ == '__main__':
+    unittest.main()