bpo-35224: PEP 572 Implementation (#10497)

* Add tokenization of :=
- Add token to Include/token.h. Add token to documentation in Doc/library/token.rst.
- Run `./python Lib/token.py` to regenerate Lib/token.py.
- Update Parser/tokenizer.c: add case to handle `:=`.

* Add initial usage of := in grammar.

* Update Python.asdl to match the grammar updates. Regenerated Include/Python-ast.h and Python/Python-ast.c

* Update AST and compiler files in Python/ast.c and Python/compile.c. Basic functionality, this isn't scoped properly

* Regenerate Lib/symbol.py using `./python Lib/symbol.py`

* Tests - Fix failing tests in test_parser.py due to changes in token numbers for internal representation

* Tests - Add simple test for := token

* Tests - Add simple tests for named expressions using expr and suite

* Tests - Update number of levels for nested expressions to prevent stack overflow

* Update symbol table to handle NamedExpr

* Update Grammar to allow assignment expressions in if statements.
Regenerate Python/graminit.c accordingly using `make regen-grammar`

* Tests - Add additional tests for named expressions in RoundtripLegalSyntaxTestCase, based on examples and information directly from PEP 572

Note: failing tests are currently commented out (4 out of 24 tests currently fail)

* Tests - Add temporary syntax test failure tests in test_parser.py

Note: There is an outstanding TODO for this -- syntax tests need to be
moved to a different file (presumably test_syntax.py), but this is
covering what needs to be tested at the moment, and it's more convenient
to run a single test for the time being

* Add support for allowing assignment expressions as function argument annotations. Uncomment tests for these cases because they all pass now!

* Tests - Move existing syntax tests out of test_parser.py and into test_named_expressions.py. Refactor syntax tests to use unittest

* Add TargetScopeError exception to extend SyntaxError

Note: This simply creates the TargetScopeError exception, it is not yet
used anywhere

* Tests - Update tests per PEP 572

Continue refactoring test suite:
The named expression test suite now checks for any invalid cases that
throw exceptions (no longer limited to SyntaxErrors), assignment tests
to ensure that variables are properly assigned, and scope tests to
ensure that variable availability and values are correct

Note:
- There are still tests that are marked to skip, as they are not yet
implemented
- There are approximately 300 lines of the PEP that have not yet been
addressed, though these may be deferred

* Documentation - Small updates to XXX/todo comments

- Remove XXX from child description in ast.c
- Add comment with number of previously supported nested expressions for
3.7.X in test_parser.py

* Fix assert in seq_for_testlist()

* Cleanup - Denote "Not implemented -- No keyword args" on failing test case. Fix PEP8 error for blank lines at beginning of test classes in test_parser.py

* Tests - Wrap all file opens in `with...as` to ensure files are closed

* WIP: handle f(a := 1)

* Tests and Cleanup - No longer skips keyword arg test. Keyword arg test now uses a simpler test case and does not rely on an external file. Remove print statements from ast.c

* Tests - Refactor last remaining test case that relied on on external file to use a simpler test case without the dependency

* Tests - Add better description of remaning skipped tests. Add test checking scope when using assignment expression in a function argument

* Tests - Add test for nested comprehension, testing value and scope. Fix variable name in skipped comprehension scope test

* Handle restriction of LHS for named expressions - can only assign to LHS of type NAME. Specifically, restrict assignment to tuples

This adds an alternative set_context specifically for named expressions,
set_namedexpr_context. Thus, context is now set differently for standard
assignment versus assignment for named expressions in order to handle
restrictions.

* Tests - Update negative test case for assigning to lambda to match new error message. Add negative test case for assigning to tuple

* Tests - Reorder test cases to group invalid syntax cases and named assignment target errors

* Tests - Update test case for named expression in function argument - check that result and variable are set correctly

* Todo - Add todo for TargetScopeError based on Guido's comment (https://github.com/python/cpython/commit/2b3acd37bdfc2d35e5094228c6684050d2aa8b0a#r30472562)

* Tests - Add named expression tests for assignment operator in function arguments

Note: One of two tests are skipped, as function arguments are currently treating
an assignment expression inside of parenthesis as one child, which does
not properly catch the named expression, nor does it count arguments
properly

* Add NamedStore to expr_context. Regenerate related code with `make regen-ast`

* Add usage of NamedStore to ast_for_named_expr in ast.c. Update occurances of checking for Store to also handle NamedStore where appropriate

* Add ste_comprehension to _symtable_entry to track if the namespace is a comprehension. Initialize ste_comprehension to 0. Set set_comprehension to 1 in symtable_handle_comprehension

* s/symtable_add_def/symtable_add_def_helper. Add symtable_add_def to handle grabbing st->st_cur and passing it to symtable_add_def_helper. This now allows us to call the original code from symtable_add_def by instead calling symtable_add_def_helper with a different ste.

* Refactor symtable_record_directive to take lineno and col_offset as arguments instead of stmt_ty. This allows symtable_record_directive to be used for stmt_ty and expr_ty

* Handle elevating scope for named expressions in comprehensions.

* Handle error for usage of named expression inside a class block

* Tests - No longer skip scope tests. Add additional scope tests

* Cleanup - Update error message for named expression within a comprehension within a class. Update comments. Add assert for symtable_extend_namedexpr_scope to validate that we always find at least a ModuleScope if we don't find a Class or FunctionScope

* Cleanup - Add missing case for NamedStore in expr_context_name. Remove unused var in set_namedexpr_content

* Refactor - Consolidate set_context and set_namedexpr_context to reduce duplicated code. Special cases for named expressions are handled by checking if ctx is NamedStore

* Cleanup - Add additional use cases for ast_for_namedexpr in usage comment. Fix multiple blank lines in test_named_expressions

* Tests - Remove unnecessary test case. Renumber test case function names

* Remove TargetScopeError for now. Will add back if needed

* Cleanup - Small comment nit for consistency

* Handle positional argument check with named expression

* Add TargetScopeError exception definition. Add documentation for TargetScopeError in c-api docs. Throw TargetScopeError instead of SyntaxError when using a named expression in a comprehension within a class scope

* Increase stack size for parser by 200. This is a minimal change (approx. 5kb) and should not have an impact on any systems. Update parser test to allow 99 nested levels again

* Add TargetScopeError to exception_hierarchy.txt for test_baseexception.py_

* Tests - Major update for named expression tests, both in test_named_expressions and test_parser

- Add test for TargetScopeError
- Add tests for named expressions in comprehension scope and edge cases
- Add tests for named expressions in function arguments (declarations
and call sites)
- Reorganize tests to group them more logically

* Cleanup - Remove unnecessary comment

* Cleanup - Comment nitpicks

* Explicitly disallow assignment expressions to a name inside parentheses, e.g.: ((x) := 0)

- Add check for LHS types to detect a parenthesis then a name (see note)
- Add test for this scenario
- Update tests for changed error message for named assignment to a tuple
(also, see note)

Note: This caused issues with the previous error handling for named assignment
to a LHS that contained an expression, such as a tuple. Thus, the check
for the LHS of a named expression must be changed to be more specific if
we wish to maintain the previous error messages

* Cleanup - Wrap lines more strictly in test file

* Revert "Explicitly disallow assignment expressions to a name inside parentheses, e.g.: ((x) := 0)"

This reverts commit f1531400ca7d7a2d148830c8ac703f041740896d.

* Add NEWS.d entry

* Tests - Fix error in test_pickle.test_exceptions by adding TargetScopeError to list of exceptions

* Tests - Update error message tests to reflect improved messaging convention (s/can't/cannot)

* Remove cases that cannot be reached in compile.c. Small linting update.

* Update Grammar/Tokens to add COLONEQUAL. Regenerate all files

* Update TargetScopeError PRE_INIT and POST_INIT, as this was purposefully left out when fixing rebase conflicts

* Add NamedStore back and regenerate files

* Pass along line number and end col info for named expression

* Simplify News entry

* Fix compiler warning and explicity mark fallthrough

4 files changed, 458 insertions, 5 deletions

diff --git a/Lib/test/exception_hierarchy.txt b/Lib/test/exception_hierarchy.txt
index 763a6c8..15f4491 100644
--- a/Lib/test/exception_hierarchy.txt
+++ b/Lib/test/exception_hierarchy.txt
@@ -42,6 +42,7 @@ BaseException
       |    +-- NotImplementedError
       |    +-- RecursionError
       +-- SyntaxError
+      |    +-- TargetScopeError
       |    +-- IndentationError
       |         +-- TabError
       +-- SystemError
diff --git a/Lib/test/test_named_expressions.py b/Lib/test/test_named_expressions.py
new file mode 100644
index 0000000..e49fd7d
--- /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()
diff --git a/Lib/test/test_parser.py b/Lib/test/test_parser.py
index 9b58bb9..ac3899b 100644
--- a/Lib/test/test_parser.py
+++ b/Lib/test/test_parser.py
@@ -115,6 +115,7 @@ class RoundtripLegalSyntaxTestCase(unittest.TestCase):
         self.check_expr("foo * bar")
         self.check_expr("foo / bar")
         self.check_expr("foo // bar")
+        self.check_expr("(foo := 1)")
         self.check_expr("lambda: 0")
         self.check_expr("lambda x: 0")
         self.check_expr("lambda *y: 0")
@@ -421,6 +422,40 @@ class RoundtripLegalSyntaxTestCase(unittest.TestCase):
         self.check_expr('{x**2:x[3] for x in seq if condition(x)}')
         self.check_expr('{x:x for x in seq1 for y in seq2 if condition(x, y)}')
 
+    def test_named_expressions(self):
+        self.check_suite("(a := 1)")
+        self.check_suite("(a := a)")
+        self.check_suite("if (match := pattern.search(data)) is None: pass")
+        self.check_suite("[y := f(x), y**2, y**3]")
+        self.check_suite("filtered_data = [y for x in data if (y := f(x)) is None]")
+        self.check_suite("(y := f(x))")
+        self.check_suite("y0 = (y1 := f(x))")
+        self.check_suite("foo(x=(y := f(x)))")
+        self.check_suite("def foo(answer=(p := 42)): pass")
+        self.check_suite("def foo(answer: (p := 42) = 5): pass")
+        self.check_suite("lambda: (x := 1)")
+        self.check_suite("(x := lambda: 1)")
+        self.check_suite("(x := lambda: (y := 1))")  # not in PEP
+        self.check_suite("lambda line: (m := re.match(pattern, line)) and m.group(1)")
+        self.check_suite("x = (y := 0)")
+        self.check_suite("(z:=(y:=(x:=0)))")
+        self.check_suite("(info := (name, phone, *rest))")
+        self.check_suite("(x:=1,2)")
+        self.check_suite("(total := total + tax)")
+        self.check_suite("len(lines := f.readlines())")
+        self.check_suite("foo(x := 3, cat='vector')")
+        self.check_suite("foo(cat=(category := 'vector'))")
+        self.check_suite("if any(len(longline := l) >= 100 for l in lines): print(longline)")
+        self.check_suite(
+            "if env_base := os.environ.get('PYTHONUSERBASE', None): return env_base"
+        )
+        self.check_suite(
+            "if self._is_special and (ans := self._check_nans(context=context)): return ans"
+        )
+        self.check_suite("foo(b := 2, a=1)")
+        self.check_suite("foo(b := 2, a=1)")
+        self.check_suite("foo((b := 2), a=1)")
+        self.check_suite("foo(c=(b := 2), a=1)")
 
 #
 #  Second, we take *invalid* trees and make sure we get ParserError
@@ -694,16 +729,16 @@ class IllegalSyntaxTestCase(unittest.TestCase):
     def test_illegal_encoding(self):
         # Illegal encoding declaration
         tree = \
-            (340,
+            (341,
              (257, (0, '')))
         self.check_bad_tree(tree, "missed encoding")
         tree = \
-            (340,
+            (341,
              (257, (0, '')),
               b'iso-8859-1')
         self.check_bad_tree(tree, "non-string encoding")
         tree = \
-            (340,
+            (341,
              (257, (0, '')),
               '\udcff')
         with self.assertRaises(UnicodeEncodeError):
@@ -776,8 +811,9 @@ class ParserStackLimitTestCase(unittest.TestCase):
         return "["*level+"]"*level
 
     def test_deeply_nested_list(self):
-        # XXX used to be 99 levels in 2.x
-        e = self._nested_expression(93)
+        # This has fluctuated between 99 levels in 2.x, down to 93 levels in
+        # 3.7.X and back up to 99 in 3.8.X. Related to MAXSTACK size in Parser.h
+        e = self._nested_expression(99)
         st = parser.expr(e)
         st.compile()
 
diff --git a/Lib/test/test_tokenize.py b/Lib/test/test_tokenize.py
index 04a1254..4c90092 100644
--- a/Lib/test/test_tokenize.py
+++ b/Lib/test/test_tokenize.py
@@ -1429,6 +1429,7 @@ class TestTokenize(TestCase):
         self.assertExactTypeEqual('**=', token.DOUBLESTAREQUAL)
         self.assertExactTypeEqual('//', token.DOUBLESLASH)
         self.assertExactTypeEqual('//=', token.DOUBLESLASHEQUAL)
+        self.assertExactTypeEqual(':=', token.COLONEQUAL)
         self.assertExactTypeEqual('...', token.ELLIPSIS)
         self.assertExactTypeEqual('->', token.RARROW)
         self.assertExactTypeEqual('@', token.AT)