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"""Unit tests for __instancecheck__ and __subclasscheck__."""
import unittest
from test import test_support
class ABC(type):
def __instancecheck__(cls, inst):
"""Implement isinstance(inst, cls)."""
return any(cls.__subclasscheck__(c)
for c in set([type(inst), inst.__class__]))
def __subclasscheck__(cls, sub):
"""Implement issubclass(sub, cls)."""
candidates = cls.__dict__.get("__subclass__", set()) | set([cls])
return any(c in candidates for c in sub.mro())
class Integer:
__metaclass__ = ABC
__subclass__ = set([int])
class SubInt(Integer):
pass
class Evil:
def __instancecheck__(self, inst): return False
class TypeChecksTest(unittest.TestCase):
def testIsSubclassInternal(self):
self.assertEqual(Integer.__subclasscheck__(int), True)
self.assertEqual(Integer.__subclasscheck__(float), False)
def testIsSubclassBuiltin(self):
self.assertEqual(issubclass(int, Integer), True)
self.assertEqual(issubclass(float, Integer), False)
def testIsInstanceBuiltin(self):
self.assertEqual(isinstance(42, Integer), True)
self.assertEqual(isinstance(3.14, Integer), False)
def testIsInstanceActual(self):
self.assertEqual(isinstance(Integer(), Integer), True)
def testIsSubclassActual(self):
self.assertEqual(issubclass(Integer, Integer), True)
def testSubclassBehavior(self):
self.assertEqual(issubclass(SubInt, Integer), True)
self.assertEqual(issubclass(SubInt, SubInt), True)
self.assertEqual(issubclass(Integer, SubInt), False)
self.assertEqual(issubclass(int, SubInt), False)
self.assertEqual(isinstance(SubInt(), Integer), True)
self.assertEqual(isinstance(SubInt(), SubInt), True)
self.assertEqual(isinstance(42, SubInt), False)
def testInfiniteRecursionCaughtProperly(self):
e = Evil()
# This invokes isinstance() recursively, until the stack is exhausted.
self.assertRaises(RuntimeError, isinstance, e, Evil)
# XXX How to check the same situation for issubclass()?
def test_main():
test_support.run_unittest(TypeChecksTest)
if __name__ == "__main__":
unittest.main()
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