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import sys
import unittest
# adapted from pyregr
class TestCause(unittest.TestCase):
def test_invalid_cause(self):
try:
raise IndexError from 5
except TypeError as e:
self.assertTrue("exception cause" in str(e))
else:
self.fail("No exception raised")
def test_raise_from_none_sets_no_cause(self):
try:
raise IndexError from None
except IndexError as e:
self.assertFalse(e.__cause__)
if sys.version_info[:2] >= (3,3):
self.assertTrue(e.__suppress_context__)
else:
self.fail("No exception raised")
def test_raise_from_none_covers_context(self):
try:
try:
raise IndexError("INDEX")
except IndexError as e:
raise ValueError("VALUE") from None
else:
self.fail("No exception raised")
except ValueError as e:
self.assertFalse(e.__cause__)
self.assertTrue(e.__context__)
if sys.version_info[:2] >= (3,3):
self.assertTrue(e.__suppress_context__)
def test_class_cause(self):
try:
raise IndexError from KeyError
except IndexError as e:
self.assertTrue(isinstance(e.__cause__, KeyError))
else:
self.fail("No exception raised")
def test_instance_cause(self):
cause = KeyError()
try:
raise IndexError from cause
except IndexError as e:
self.assertTrue(e.__cause__ is cause)
else:
self.fail("No exception raised")
def test_erroneous_cause(self):
class MyException(Exception):
def __init__(self):
raise RuntimeError()
try:
raise IndexError from MyException
except RuntimeError:
pass
else:
self.fail("No exception raised")
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