import unittest import builtins import os from platform import system as platform_system class ExceptionClassTests(unittest.TestCase): """Tests for anything relating to exception objects themselves (e.g., inheritance hierarchy)""" def test_builtins_new_style(self): self.assertTrue(issubclass(Exception, object)) def verify_instance_interface(self, ins): for attr in ("args", "__str__", "__repr__"): self.assertTrue(hasattr(ins, attr), "%s missing %s attribute" % (ins.__class__.__name__, attr)) def test_inheritance(self): # Make sure the inheritance hierarchy matches the documentation exc_set = set() for object_ in builtins.__dict__.values(): try: if issubclass(object_, BaseException): exc_set.add(object_.__name__) except TypeError: pass inheritance_tree = open( os.path.join(os.path.split(__file__)[0], 'exception_hierarchy.txt'), encoding="utf-8") try: superclass_name = inheritance_tree.readline().rstrip() try: last_exc = getattr(builtins, superclass_name) except AttributeError: self.fail("base class %s not a built-in" % superclass_name) self.assertIn(superclass_name, exc_set, '%s not found' % superclass_name) exc_set.discard(superclass_name) superclasses = [] # Loop will insert base exception last_depth = 0 for exc_line in inheritance_tree: exc_line = exc_line.rstrip() depth = exc_line.rindex('─') exc_name = exc_line[depth+2:] # Slice past space if '(' in exc_name: paren_index = exc_name.index('(') platform_name = exc_name[paren_index+1:-1] exc_name = exc_name[:paren_index-1] # Slice off space if platform_system() != platform_name: exc_set.discard(exc_name) continue if '[' in exc_name: left_bracket = exc_name.index('[') exc_name = exc_name[:left_bracket-1] # cover space try: exc = getattr(builtins, exc_name) except AttributeError: self.fail("%s not a built-in exception" % exc_name) if last_depth < depth: superclasses.append((last_depth, last_exc)) elif last_depth > depth: while superclasses[-1][0] >= depth: superclasses.pop() self.assertTrue(issubclass(exc, superclasses[-1][1]), "%s is not a subclass of %s" % (exc.__name__, superclasses[-1][1].__name__)) try: # Some exceptions require arguments; just skip them self.verify_instance_interface(exc()) except TypeError: pass self.assertIn(exc_name, exc_set) exc_set.discard(exc_name) last_exc = exc last_depth = depth finally: inheritance_tree.close() # Underscore-prefixed (private) exceptions don't need to be documented exc_set = set(e for e in exc_set if not e.startswith('_')) self.assertEqual(len(exc_set), 0, "%s not accounted for" % exc_set) interface_tests = ("length", "args", "str", "repr") def interface_test_driver(self, results): for test_name, (given, expected) in zip(self.interface_tests, results): self.assertEqual(given, expected, "%s: %s != %s" % (test_name, given, expected)) def test_interface_single_arg(self): # Make sure interface works properly when given a single argument arg = "spam" exc = Exception(arg) results = ([len(exc.args), 1], [exc.args[0], arg], [str(exc), str(arg)], [repr(exc), '%s(%r)' % (exc.__class__.__name__, arg)]) self.interface_test_driver(results) def test_interface_multi_arg(self): # Make sure interface correct when multiple arguments given arg_count = 3 args = tuple(range(arg_count)) exc = Exception(*args) results = ([len(exc.args), arg_count], [exc.args, args], [str(exc), str(args)], [repr(exc), exc.__class__.__name__ + repr(exc.args)]) self.interface_test_driver(results) def test_interface_no_arg(self): # Make sure that with no args that interface is correct exc = Exception() results = ([len(exc.args), 0], [exc.args, tuple()], [str(exc), ''], [repr(exc), exc.__class__.__name__ + '()']) self.interface_test_driver(results) def test_setstate_refcount_no_crash(self): # gh-97591: Acquire strong reference before calling tp_hash slot # in PyObject_SetAttr. import gc d = {} class HashThisKeyWillClearTheDict(str): def __hash__(self) -> int: d.clear() return super().__hash__() class Value(str): pass exc = Exception() d[HashThisKeyWillClearTheDict()] = Value() # refcount of Value() is 1 now # Exception.__setstate__ should acquire a strong reference of key and # value in the dict. Otherwise, Value()'s refcount would go below # zero in the tp_hash call in PyObject_SetAttr(), and it would cause # crash in GC. exc.__setstate__(d) # __hash__() is called again here, clearing the dict. # This GC would crash if the refcount of Value() goes below zero. gc.collect() class UsageTests(unittest.TestCase): """Test usage of exceptions""" def raise_fails(self, object_): """Make sure that raising 'object_' triggers a TypeError.""" try: raise object_ except TypeError: return # What is expected. self.fail("TypeError expected for raising %s" % type(object_)) def catch_fails(self, object_): """Catching 'object_' should raise a TypeError.""" try: try: raise Exception except object_: pass except TypeError: pass except Exception: self.fail("TypeError expected when catching %s" % type(object_)) try: try: raise Exception except (object_,): pass except TypeError: return except Exception: self.fail("TypeError expected when catching %s as specified in a " "tuple" % type(object_)) def test_raise_new_style_non_exception(self): # You cannot raise a new-style class that does not inherit from # BaseException; the ability was not possible until BaseException's # introduction so no need to support new-style objects that do not # inherit from it. class NewStyleClass(object): pass self.raise_fails(NewStyleClass) self.raise_fails(NewStyleClass()) def test_raise_string(self): # Raising a string raises TypeError. self.raise_fails("spam") def test_catch_non_BaseException(self): # Trying to catch an object that does not inherit from BaseException # is not allowed. class NonBaseException(object): pass self.catch_fails(NonBaseException) self.catch_fails(NonBaseException()) def test_catch_BaseException_instance(self): # Catching an instance of a BaseException subclass won't work. self.catch_fails(BaseException()) def test_catch_string(self): # Catching a string is bad. self.catch_fails("spam") if __name__ == '__main__': unittest.main()