Lib/test/test_typechecks.py

   1 """Unit tests for __instancecheck__ and __subclasscheck__."""
   2
   3 import unittest
   4 from test import test_support
   5
   6
   7 class ABC(type):
   8
   9     def __instancecheck__(cls, inst):
  10         """Implement isinstance(inst, cls)."""
  11         return any(cls.__subclasscheck__(c)
  12                    for c in set([type(inst), inst.__class__]))
  13
  14     def __subclasscheck__(cls, sub):
  15         """Implement issubclass(sub, cls)."""
  16         candidates = cls.__dict__.get("__subclass__", set()) | set([cls])
  17         return any(c in candidates for c in sub.mro())
  18
  19
  20 class Integer:
  21
  22     __metaclass__ = ABC
  23
  24     __subclass__ = set([int])
  25
  26
  27 class SubInt(Integer):
  28
  29     pass
  30
  31
  32 class TypeChecksTest(unittest.TestCase):
  33
  34     def testIsSubclassInternal(self):
  35         self.assertEqual(Integer.__subclasscheck__(int), True)
  36         self.assertEqual(Integer.__subclasscheck__(float), False)
  37
  38     def testIsSubclassBuiltin(self):
  39         self.assertEqual(issubclass(int, Integer), True)
  40         self.assertEqual(issubclass(int, (Integer,)), True)
  41         self.assertEqual(issubclass(float, Integer), False)
  42         self.assertEqual(issubclass(float, (Integer,)), False)
  43
  44     def testIsInstanceBuiltin(self):
  45         self.assertEqual(isinstance(42, Integer), True)
  46         self.assertEqual(isinstance(42, (Integer,)), True)
  47         self.assertEqual(isinstance(3.14, Integer), False)
  48         self.assertEqual(isinstance(3.14, (Integer,)), False)
  49
  50     def testIsInstanceActual(self):
  51         self.assertEqual(isinstance(Integer(), Integer), True)
  52         self.assertEqual(isinstance(Integer(), (Integer,)), True)
  53
  54     def testIsSubclassActual(self):
  55         self.assertEqual(issubclass(Integer, Integer), True)
  56         self.assertEqual(issubclass(Integer, (Integer,)), True)
  57
  58     def testSubclassBehavior(self):
  59         self.assertEqual(issubclass(SubInt, Integer), True)
  60         self.assertEqual(issubclass(SubInt, (Integer,)), True)
  61         self.assertEqual(issubclass(SubInt, SubInt), True)
  62         self.assertEqual(issubclass(SubInt, (SubInt,)), True)
  63         self.assertEqual(issubclass(Integer, SubInt), False)
  64         self.assertEqual(issubclass(Integer, (SubInt,)), False)
  65         self.assertEqual(issubclass(int, SubInt), False)
  66         self.assertEqual(issubclass(int, (SubInt,)), False)
  67         self.assertEqual(isinstance(SubInt(), Integer), True)
  68         self.assertEqual(isinstance(SubInt(), (Integer,)), True)
  69         self.assertEqual(isinstance(SubInt(), SubInt), True)
  70         self.assertEqual(isinstance(SubInt(), (SubInt,)), True)
  71         self.assertEqual(isinstance(42, SubInt), False)
  72         self.assertEqual(isinstance(42, (SubInt,)), False)
  73
  74     def test_oldstyle(self):
  75         # These should just be ignored.
  76         class X:
  77             def __instancecheck__(self, inst):
  78                 return True
  79             def __subclasscheck__(self, cls):
  80                 return True
  81         class Sub(X): pass
  82         self.assertFalse(isinstance(3, X))
  83         self.assertTrue(isinstance(X(), X))
  84         self.assertFalse(issubclass(int, X))
  85         self.assertTrue(issubclass(Sub, X))
  86
  87
  88 def test_main():
  89     test_support.run_unittest(TypeChecksTest)
  90
  91
  92 if __name__ == "__main__":
  93     unittest.main()