import doctest import unittest doctests = """ Unpack tuple >>> t = (1, 2, 3) >>> a, b, c = t >>> a == 1 and b == 2 and c == 3 True Unpack list >>> l = [4, 5, 6] >>> a, b, c = l >>> a == 4 and b == 5 and c == 6 True Unpack implied tuple >>> a, b, c = 7, 8, 9 >>> a == 7 and b == 8 and c == 9 True Unpack string... fun! >>> a, b, c = 'one' >>> a == 'o' and b == 'n' and c == 'e' True Unpack generic sequence >>> class Seq: ... def __getitem__(self, i): ... if i >= 0 and i < 3: return i ... raise IndexError ... >>> a, b, c = Seq() >>> a == 0 and b == 1 and c == 2 True Single element unpacking, with extra syntax >>> st = (99,) >>> sl = [100] >>> a, = st >>> a 99 >>> b, = sl >>> b 100 Now for some failures Unpacking non-sequence >>> a, b, c = 7 Traceback (most recent call last): ... TypeError: cannot unpack non-iterable int object Unpacking tuple of wrong size >>> a, b = t Traceback (most recent call last): ... ValueError: too many values to unpack (expected 2) Unpacking tuple of wrong size >>> a, b = l Traceback (most recent call last): ... ValueError: too many values to unpack (expected 2) Unpacking sequence too short >>> a, b, c, d = Seq() Traceback (most recent call last): ... ValueError: not enough values to unpack (expected 4, got 3) Unpacking sequence too long >>> a, b = Seq() Traceback (most recent call last): ... ValueError: too many values to unpack (expected 2) Unpacking a sequence where the test for too long raises a different kind of error >>> class BozoError(Exception): ... pass ... >>> class BadSeq: ... def __getitem__(self, i): ... if i >= 0 and i < 3: ... return i ... elif i == 3: ... raise BozoError ... else: ... raise IndexError ... Trigger code while not expecting an IndexError (unpack sequence too long, wrong error) >>> a, b, c, d, e = BadSeq() Traceback (most recent call last): ... test.test_unpack.BozoError Trigger code while expecting an IndexError (unpack sequence too short, wrong error) >>> a, b, c = BadSeq() Traceback (most recent call last): ... test.test_unpack.BozoError Allow unpacking empty iterables >>> () = [] >>> [] = () >>> [] = [] >>> () = () Unpacking non-iterables should raise TypeError >>> () = 42 Traceback (most recent call last): ... TypeError: cannot unpack non-iterable int object Unpacking to an empty iterable should raise ValueError >>> () = [42] Traceback (most recent call last): ... ValueError: too many values to unpack (expected 0) """ __test__ = {'doctests' : doctests} def load_tests(loader, tests, pattern): tests.addTest(doctest.DocTestSuite()) return tests class TestCornerCases(unittest.TestCase): def test_extended_oparg_not_ignored(self): # https://github.com/python/cpython/issues/91625 target = "(" + "y,"*400 + ")" code = f"""def unpack_400(x): {target} = x return y """ ns = {} exec(code, ns) unpack_400 = ns["unpack_400"] # Warm up the function for quickening (PEP 659) for _ in range(30): y = unpack_400(range(400)) self.assertEqual(y, 399) if __name__ == "__main__": unittest.main()