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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()
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)
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()
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