1 files changed, 415 insertions, 0 deletions
diff --git a/Lib/test/test_named_expressions.py b/Lib/test/test_named_expressions.py
new file mode 100644
index 0000000000..e49fd7de20
--- /dev/null
+++ b/Lib/test/test_named_expressions.py
@@ -0,0 +1,415 @@
+import os
+import unittest
+
+
+class NamedExpressionInvalidTest(unittest.TestCase):
+
+    def test_named_expression_invalid_01(self):
+        code = """x := 0"""
+
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_02(self):
+        code = """x = y := 0"""
+
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_03(self):
+        code = """y := f(x)"""
+
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_04(self):
+        code = """y0 = y1 := f(x)"""
+
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_06(self):
+        code = """((a, b) := (1, 2))"""
+
+        with self.assertRaisesRegex(SyntaxError, "cannot use named assignment with tuple"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_07(self):
+        code = """def spam(a = b := 42): pass"""
+
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_08(self):
+        code = """def spam(a: b := 42 = 5): pass"""
+
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_09(self):
+        code = """spam(a=b := 'c')"""
+
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_10(self):
+        code = """spam(x = y := f(x))"""
+
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_11(self):
+        code = """spam(a=1, b := 2)"""
+
+        with self.assertRaisesRegex(SyntaxError,
+            "positional argument follows keyword argument"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_12(self):
+        code = """spam(a=1, (b := 2))"""
+
+        with self.assertRaisesRegex(SyntaxError,
+            "positional argument follows keyword argument"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_13(self):
+        code = """spam(a=1, (b := 2))"""
+
+        with self.assertRaisesRegex(SyntaxError,
+            "positional argument follows keyword argument"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_14(self):
+        code = """(x := lambda: y := 1)"""
+
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_15(self):
+        code = """(lambda: x := 1)"""
+
+        with self.assertRaisesRegex(SyntaxError,
+            "cannot use named assignment with lambda"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_16(self):
+        code = "[i + 1 for i in i := [1,2]]"
+
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_17(self):
+        code = "[i := 0, j := 1 for i, j in [(1, 2), (3, 4)]]"
+
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
+            exec(code, {}, {})
+
+    def test_named_expression_invalid_18(self):
+        code = """class Foo():
+            [(42, 1 + ((( j := i )))) for i in range(5)]
+        """
+
+        with self.assertRaisesRegex(TargetScopeError,
+            "named expression within a comprehension cannot be used in a class body"):
+            exec(code, {}, {})
+
+
+class NamedExpressionAssignmentTest(unittest.TestCase):
+
+    def test_named_expression_assignment_01(self):
+        (a := 10)
+
+        self.assertEqual(a, 10)
+
+    def test_named_expression_assignment_02(self):
+        a = 20
+        (a := a)
+
+        self.assertEqual(a, 20)
+
+    def test_named_expression_assignment_03(self):
+        (total := 1 + 2)
+
+        self.assertEqual(total, 3)
+
+    def test_named_expression_assignment_04(self):
+        (info := (1, 2, 3))
+
+        self.assertEqual(info, (1, 2, 3))
+
+    def test_named_expression_assignment_05(self):
+        (x := 1, 2)
+
+        self.assertEqual(x, 1)
+
+    def test_named_expression_assignment_06(self):
+        (z := (y := (x := 0)))
+
+        self.assertEqual(x, 0)
+        self.assertEqual(y, 0)
+        self.assertEqual(z, 0)
+
+    def test_named_expression_assignment_07(self):
+        (loc := (1, 2))
+
+        self.assertEqual(loc, (1, 2))
+
+    def test_named_expression_assignment_08(self):
+        if spam := "eggs":
+            self.assertEqual(spam, "eggs")
+        else: self.fail("variable was not assigned using named expression")
+
+    def test_named_expression_assignment_09(self):
+        if True and (spam := True):
+            self.assertTrue(spam)
+        else: self.fail("variable was not assigned using named expression")
+
+    def test_named_expression_assignment_10(self):
+        if (match := 10) is 10:
+            pass
+        else: self.fail("variable was not assigned using named expression")
+
+    def test_named_expression_assignment_11(self):
+        def spam(a):
+            return a
+        input_data = [1, 2, 3]
+        res = [(x, y, x/y) for x in input_data if (y := spam(x)) > 0]
+
+        self.assertEqual(res, [(1, 1, 1.0), (2, 2, 1.0), (3, 3, 1.0)])
+
+    def test_named_expression_assignment_12(self):
+        def spam(a):
+            return a
+        res = [[y := spam(x), x/y] for x in range(1, 5)]
+
+        self.assertEqual(res, [[1, 1.0], [2, 1.0], [3, 1.0], [4, 1.0]])
+
+    def test_named_expression_assignment_13(self):
+        length = len(lines := [1, 2])
+
+        self.assertEqual(length, 2)
+        self.assertEqual(lines, [1,2])
+
+    def test_named_expression_assignment_14(self):
+        """
+        Where all variables are positive integers, and a is at least as large
+        as the n'th root of x, this algorithm returns the floor of the n'th
+        root of x (and roughly doubling the number of accurate bits per
+        iteration)::
+        """
+        a = 9
+        n = 2
+        x = 3
+
+        while a > (d := x // a**(n-1)):
+            a = ((n-1)*a + d) // n
+
+        self.assertEqual(a, 1)
+
+
+class NamedExpressionScopeTest(unittest.TestCase):
+
+    def test_named_expression_scope_01(self):
+        code = """def spam():
+    (a := 5)
+print(a)"""
+
+        with self.assertRaisesRegex(NameError, "name 'a' is not defined"):
+            exec(code, {}, {})
+
+    def test_named_expression_scope_02(self):
+        total = 0
+        partial_sums = [total := total + v for v in range(5)]
+
+        self.assertEqual(partial_sums, [0, 1, 3, 6, 10])
+        self.assertEqual(total, 10)
+
+    def test_named_expression_scope_03(self):
+        containsOne = any((lastNum := num) == 1 for num in [1, 2, 3])
+
+        self.assertTrue(containsOne)
+        self.assertEqual(lastNum, 1)
+
+    def test_named_expression_scope_04(self):
+        def spam(a):
+            return a
+        res = [[y := spam(x), x/y] for x in range(1, 5)]
+
+        self.assertEqual(y, 4)
+
+    def test_named_expression_scope_05(self):
+        def spam(a):
+            return a
+        input_data = [1, 2, 3]
+        res = [(x, y, x/y) for x in input_data if (y := spam(x)) > 0]
+
+        self.assertEqual(res, [(1, 1, 1.0), (2, 2, 1.0), (3, 3, 1.0)])
+        self.assertEqual(y, 3)
+
+    def test_named_expression_scope_06(self):
+        res = [[spam := i for i in range(3)] for j in range(2)]
+
+        self.assertEqual(res, [[0, 1, 2], [0, 1, 2]])
+        self.assertEqual(spam, 2)
+
+    def test_named_expression_scope_07(self):
+        len(lines := [1, 2])
+
+        self.assertEqual(lines, [1, 2])
+
+    def test_named_expression_scope_08(self):
+        def spam(a):
+            return a
+
+        def eggs(b):
+            return b * 2
+
+        res = [spam(a := eggs(b := h)) for h in range(2)]
+
+        self.assertEqual(res, [0, 2])
+        self.assertEqual(a, 2)
+        self.assertEqual(b, 1)
+
+    def test_named_expression_scope_09(self):
+        def spam(a):
+            return a
+
+        def eggs(b):
+            return b * 2
+
+        res = [spam(a := eggs(a := h)) for h in range(2)]
+
+        self.assertEqual(res, [0, 2])
+        self.assertEqual(a, 2)
+
+    def test_named_expression_scope_10(self):
+        res = [b := [a := 1 for i in range(2)] for j in range(2)]
+
+        self.assertEqual(res, [[1, 1], [1, 1]])
+        self.assertEqual(a, 1)
+        self.assertEqual(b, [1, 1])
+
+    def test_named_expression_scope_11(self):
+        res = [j := i for i in range(5)]
+
+        self.assertEqual(res, [0, 1, 2, 3, 4])
+        self.assertEqual(j, 4)
+
+    def test_named_expression_scope_12(self):
+        res = [i := i for i in range(5)]
+
+        self.assertEqual(res, [0, 1, 2, 3, 4])
+        self.assertEqual(i, 4)
+
+    def test_named_expression_scope_13(self):
+        res = [i := 0 for i, j in [(1, 2), (3, 4)]]
+
+        self.assertEqual(res, [0, 0])
+        self.assertEqual(i, 0)
+
+    def test_named_expression_scope_14(self):
+        res = [(i := 0, j := 1) for i, j in [(1, 2), (3, 4)]]
+
+        self.assertEqual(res, [(0, 1), (0, 1)])
+        self.assertEqual(i, 0)
+        self.assertEqual(j, 1)
+
+    def test_named_expression_scope_15(self):
+        res = [(i := i, j := j) for i, j in [(1, 2), (3, 4)]]
+
+        self.assertEqual(res, [(1, 2), (3, 4)])
+        self.assertEqual(i, 3)
+        self.assertEqual(j, 4)
+
+    def test_named_expression_scope_16(self):
+        res = [(i := j, j := i) for i, j in [(1, 2), (3, 4)]]
+
+        self.assertEqual(res, [(2, 2), (4, 4)])
+        self.assertEqual(i, 4)
+        self.assertEqual(j, 4)
+
+    def test_named_expression_scope_17(self):
+        b = 0
+        res = [b := i + b for i in range(5)]
+
+        self.assertEqual(res, [0, 1, 3, 6, 10])
+        self.assertEqual(b, 10)
+
+    def test_named_expression_scope_18(self):
+        def spam(a):
+            return a
+
+        res = spam(b := 2)
+
+        self.assertEqual(res, 2)
+        self.assertEqual(b, 2)
+
+    def test_named_expression_scope_19(self):
+        def spam(a):
+            return a
+
+        res = spam((b := 2))
+
+        self.assertEqual(res, 2)
+        self.assertEqual(b, 2)
+
+    def test_named_expression_scope_20(self):
+        def spam(a):
+            return a
+
+        res = spam(a=(b := 2))
+
+        self.assertEqual(res, 2)
+        self.assertEqual(b, 2)
+
+    def test_named_expression_scope_21(self):
+        def spam(a, b):
+            return a + b
+
+        res = spam(c := 2, b=1)
+
+        self.assertEqual(res, 3)
+        self.assertEqual(c, 2)
+
+    def test_named_expression_scope_22(self):
+        def spam(a, b):
+            return a + b
+
+        res = spam((c := 2), b=1)
+
+        self.assertEqual(res, 3)
+        self.assertEqual(c, 2)
+
+    def test_named_expression_scope_23(self):
+        def spam(a, b):
+            return a + b
+
+        res = spam(b=(c := 2), a=1)
+
+        self.assertEqual(res, 3)
+        self.assertEqual(c, 2)
+
+    def test_named_expression_scope_24(self):
+        a = 10
+        def spam():
+            nonlocal a
+            (a := 20)
+        spam()
+
+        self.assertEqual(a, 20)
+
+    def test_named_expression_scope_25(self):
+        ns = {}
+        code = """a = 10
+def spam():
+    global a
+    (a := 20)
+spam()"""
+
+        exec(code, ns, {})
+
+        self.assertEqual(ns["a"], 20)
+
+
+if __name__ == "__main__":
+    unittest.main()