"""Unit tests for the with statement specified in PEP 343."""
__author__ = "Mike Bland"
__email__ = "mbland at acm dot org"
import sys
import traceback
import unittest
from collections import deque
from contextlib import _GeneratorContextManager, contextmanager, nullcontext
class MockContextManager(_GeneratorContextManager):
def __init__(self, *args):
super().__init__(*args)
self.enter_called = False
self.exit_called = False
self.exit_args = None
def __enter__(self):
self.enter_called = True
return _GeneratorContextManager.__enter__(self)
def __exit__(self, type, value, traceback):
self.exit_called = True
self.exit_args = (type, value, traceback)
return _GeneratorContextManager.__exit__(self, type,
value, traceback)
def mock_contextmanager(func):
def helper(*args, **kwds):
return MockContextManager(func, args, kwds)
return helper
class MockResource(object):
def __init__(self):
self.yielded = False
self.stopped = False
@mock_contextmanager
def mock_contextmanager_generator():
mock = MockResource()
try:
mock.yielded = True
yield mock
finally:
mock.stopped = True
class Nested(object):
def __init__(self, *managers):
self.managers = managers
self.entered = None
def __enter__(self):
if self.entered is not None:
raise RuntimeError("Context is not reentrant")
self.entered = deque()
vars = []
try:
for mgr in self.managers:
vars.append(mgr.__enter__())
self.entered.appendleft(mgr)
except:
if not self.__exit__(*sys.exc_info()):
raise
return vars
def __exit__(self, *exc_info):
# Behave like nested with statements
# first in, last out
# New exceptions override old ones
ex = exc_info
for mgr in self.entered:
try:
if mgr.__exit__(*ex):
ex = (None, None, None)
except BaseException as e:
ex = (type(e), e, e.__traceback__)
self.entered = None
if ex is not exc_info:
raise ex
class MockNested(Nested):
def __init__(self, *managers):
Nested.__init__(self, *managers)
self.enter_called = False
self.exit_called = False
self.exit_args = None
def __enter__(self):
self.enter_called = True
return Nested.__enter__(self)
def __exit__(self, *exc_info):
self.exit_called = True
self.exit_args = exc_info
return Nested.__exit__(self, *exc_info)
class FailureTestCase(unittest.TestCase):
def testNameError(self):
def fooNotDeclared():
with foo: pass
self.assertRaises(NameError, fooNotDeclared)
def testEnterAttributeError1(self):
class LacksEnter(object):
def __exit__(self, type, value, traceback):
pass
def fooLacksEnter():
foo = LacksEnter()
with foo: pass
self.assertRaisesRegex(TypeError, 'the context manager', fooLacksEnter)
def testEnterAttributeError2(self):
class LacksEnterAndExit(object):
pass
def fooLacksEnterAndExit():
foo = LacksEnterAndExit()
with foo: pass
self.assertRaisesRegex(TypeError, 'the context manager', fooLacksEnterAndExit)
def testExitAttributeError(self):
class LacksExit(object):
def __enter__(self):
pass
def fooLacksExit():
foo = LacksExit()
with foo: pass
self.assertRaisesRegex(TypeError, 'the context manager.*__exit__', fooLacksExit)
def assertRaisesSyntaxError(self, codestr):
def shouldRaiseSyntaxError(s):
compile(s, '', 'single')
self.assertRaises(SyntaxError, shouldRaiseSyntaxError, codestr)
def testAssignmentToNoneError(self):
self.assertRaisesSyntaxError('with mock as None:\n pass')
self.assertRaisesSyntaxError(
'with mock as (None):\n'
' pass')
def testAssignmentToTupleOnlyContainingNoneError(self):
self.assertRaisesSyntaxError('with mock as None,:\n pass')
self.assertRaisesSyntaxError(
'with mock as (None,):\n'
' pass')
def testAssignmentToTupleContainingNoneError(self):
self.assertRaisesSyntaxError(
'with mock as (foo, None, bar):\n'
' pass')
def testEnterThrows(self):
class EnterThrows(object):
def __enter__(self):
raise RuntimeError("Enter threw")
def __exit__(self, *args):
pass
def shouldThrow():
ct = EnterThrows()
self.foo = None
# Ruff complains that we're redefining `self.foo` here,
# but the whole point of the test is to check that `self.foo`
# is *not* redefined (because `__enter__` raises)
with ct as self.foo: # ruff: noqa: F811
pass
self.assertRaises(RuntimeError, shouldThrow)
self.assertEqual(self.foo, None)
def testExitThrows(self):
class ExitThrows(object):
def __enter__(self):
return
def __exit__(self, *args):
raise RuntimeError(42)
def shouldThrow():
with ExitThrows():
pass
self.assertRaises(RuntimeError, shouldThrow)
class ContextmanagerAssertionMixin(object):
def setUp(self):
self.TEST_EXCEPTION = RuntimeError("test exception")
def assertInWithManagerInvariants(self, mock_manager):
self.assertTrue(mock_manager.enter_called)
self.assertFalse(mock_manager.exit_called)
self.assertEqual(mock_manager.exit_args, None)
def assertAfterWithManagerInvariants(self, mock_manager, exit_args):
self.assertTrue(mock_manager.enter_called)
self.assertTrue(mock_manager.exit_called)
self.assertEqual(mock_manager.exit_args, exit_args)
def assertAfterWithManagerInvariantsNoError(self, mock_manager):
self.assertAfterWithManagerInvariants(mock_manager,
(None, None, None))
def assertInWithGeneratorInvariants(self, mock_generator):
self.assertTrue(mock_generator.yielded)
self.assertFalse(mock_generator.stopped)
def assertAfterWithGeneratorInvariantsNoError(self, mock_generator):
self.assertTrue(mock_generator.yielded)
self.assertTrue(mock_generator.stopped)
def raiseTestException(self):
raise self.TEST_EXCEPTION
def assertAfterWithManagerInvariantsWithError(self, mock_manager,
exc_type=None):
self.assertTrue(mock_manager.enter_called)
self.assertTrue(mock_manager.exit_called)
if exc_type is None:
self.assertEqual(mock_manager.exit_args[1], self.TEST_EXCEPTION)
exc_type = type(self.TEST_EXCEPTION)
self.assertEqual(mock_manager.exit_args[0], exc_type)
# Test the __exit__ arguments. Issue #7853
self.assertIsInstance(mock_manager.exit_args[1], exc_type)
self.assertIsNot(mock_manager.exit_args[2], None)
def assertAfterWithGeneratorInvariantsWithError(self, mock_generator):
self.assertTrue(mock_generator.yielded)
self.assertTrue(mock_generator.stopped)
class NonexceptionalTestCase(unittest.TestCase, ContextmanagerAssertionMixin):
def testInlineGeneratorSyntax(self):
with mock_contextmanager_generator():
pass
def testUnboundGenerator(self):
mock = mock_contextmanager_generator()
with mock:
pass
self.assertAfterWithManagerInvariantsNoError(mock)
def testInlineGeneratorBoundSyntax(self):
with mock_contextmanager_generator() as foo:
self.assertInWithGeneratorInvariants(foo)
# FIXME: In the future, we'll try to keep the bound names from leaking
self.assertAfterWithGeneratorInvariantsNoError(foo)
def testInlineGeneratorBoundToExistingVariable(self):
with mock_contextmanager_generator() as foo:
self.assertInWithGeneratorInvariants(foo)
self.assertAfterWithGeneratorInvariantsNoError(foo)
def testInlineGeneratorBoundToDottedVariable(self):
with mock_contextmanager_generator() as self.foo:
self.assertInWithGeneratorInvariants(self.foo)
self.assertAfterWithGeneratorInvariantsNoError(self.foo)
def testBoundGenerator(self):
mock = mock_contextmanager_generator()
with mock as foo:
self.assertInWithGeneratorInvariants(foo)
self.assertInWithManagerInvariants(mock)
self.assertAfterWithGeneratorInvariantsNoError(foo)
self.assertAfterWithManagerInvariantsNoError(mock)
def testNestedSingleStatements(self):
mock_a = mock_contextmanager_generator()
with mock_a as foo:
mock_b = mock_contextmanager_generator()
with mock_b as bar:
self.assertInWithManagerInvariants(mock_a)
self.assertInWithManagerInvariants(mock_b)
self.assertInWithGeneratorInvariants(foo)
self.assertInWithGeneratorInvariants(bar)
self.assertAfterWithManagerInvariantsNoError(mock_b)
self.assertAfterWithGeneratorInvariantsNoError(bar)
self.assertInWithManagerInvariants(mock_a)
self.assertInWithGeneratorInvariants(foo)
self.assertAfterWithManagerInvariantsNoError(mock_a)
self.assertAfterWithGeneratorInvariantsNoError(foo)
class NestedNonexceptionalTestCase(unittest.TestCase,
ContextmanagerAssertionMixin):
def testSingleArgInlineGeneratorSyntax(self):
with Nested(mock_contextmanager_generator()):
pass
def testSingleArgBoundToNonTuple(self):
m = mock_contextmanager_generator()
# This will bind all the arguments to nested() into a single list
# assigned to foo.
with Nested(m) as foo:
self.assertInWithManagerInvariants(m)
self.assertAfterWithManagerInvariantsNoError(m)
def testSingleArgBoundToSingleElementParenthesizedList(self):
m = mock_contextmanager_generator()
# This will bind all the arguments to nested() into a single list
# assigned to foo.
with Nested(m) as (foo):
self.assertInWithManagerInvariants(m)
self.assertAfterWithManagerInvariantsNoError(m)
def testSingleArgBoundToMultipleElementTupleError(self):
def shouldThrowValueError():
with Nested(mock_contextmanager_generator()) as (foo, bar):
pass
self.assertRaises(ValueError, shouldThrowValueError)
def testSingleArgUnbound(self):
mock_contextmanager = mock_contextmanager_generator()
mock_nested = MockNested(mock_contextmanager)
with mock_nested:
self.assertInWithManagerInvariants(mock_contextmanager)
self.assertInWithManagerInvariants(mock_nested)
self.assertAfterWithManagerInvariantsNoError(mock_contextmanager)
self.assertAfterWithManagerInvariantsNoError(mock_nested)
def testMultipleArgUnbound(self):
m = mock_contextmanager_generator()
n = mock_contextmanager_generator()
o = mock_contextmanager_generator()
mock_nested = MockNested(m, n, o)
with mock_nested:
self.assertInWithManagerInvariants(m)
self.assertInWithManagerInvariants(n)
self.assertInWithManagerInvariants(o)
self.assertInWithManagerInvariants(mock_nested)
self.assertAfterWithManagerInvariantsNoError(m)
self.assertAfterWithManagerInvariantsNoError(n)
self.assertAfterWithManagerInvariantsNoError(o)
self.assertAfterWithManagerInvariantsNoError(mock_nested)
def testMultipleArgBound(self):
mock_nested = MockNested(mock_contextmanager_generator(),
mock_contextmanager_generator(), mock_contextmanager_generator())
with mock_nested as (m, n, o):
self.assertInWithGeneratorInvariants(m)
self.assertInWithGeneratorInvariants(n)
self.assertInWithGeneratorInvariants(o)
self.assertInWithManagerInvariants(mock_nested)
self.assertAfterWithGeneratorInvariantsNoError(m)
self.assertAfterWithGeneratorInvariantsNoError(n)
self.assertAfterWithGeneratorInvariantsNoError(o)
self.assertAfterWithManagerInvariantsNoError(mock_nested)
class ExceptionalTestCase(ContextmanagerAssertionMixin, unittest.TestCase):
def testSingleResource(self):
cm = mock_contextmanager_generator()
def shouldThrow():
with cm as self.resource:
self.assertInWithManagerInvariants(cm)
self.assertInWithGeneratorInvariants(self.resource)
self.raiseTestException()
self.assertRaises(RuntimeError, shouldThrow)
self.assertAfterWithManagerInvariantsWithError(cm)
self.assertAfterWithGeneratorInvariantsWithError(self.resource)
def testExceptionNormalized(self):
cm = mock_contextmanager_generator()
def shouldThrow():
with cm as self.resource:
# Note this relies on the fact that 1 // 0 produces an exception
# that is not normalized immediately.
1 // 0
self.assertRaises(ZeroDivisionError, shouldThrow)
self.assertAfterWithManagerInvariantsWithError(cm, ZeroDivisionError)
def testNestedSingleStatements(self):
mock_a = mock_contextmanager_generator()
mock_b = mock_contextmanager_generator()
def shouldThrow():
with mock_a as self.foo:
with mock_b as self.bar:
self.assertInWithManagerInvariants(mock_a)
self.assertInWithManagerInvariants(mock_b)
self.assertInWithGeneratorInvariants(self.foo)
self.assertInWithGeneratorInvariants(self.bar)
self.raiseTestException()
self.assertRaises(RuntimeError, shouldThrow)
self.assertAfterWithManagerInvariantsWithError(mock_a)
self.assertAfterWithManagerInvariantsWithError(mock_b)
self.assertAfterWithGeneratorInvariantsWithError(self.foo)
self.assertAfterWithGeneratorInvariantsWithError(self.bar)
def testMultipleResourcesInSingleStatement(self):
cm_a = mock_contextmanager_generator()
cm_b = mock_contextmanager_generator()
mock_nested = MockNested(cm_a, cm_b)
def shouldThrow():
with mock_nested as (self.resource_a, self.resource_b):
self.assertInWithManagerInvariants(cm_a)
self.assertInWithManagerInvariants(cm_b)
self.assertInWithManagerInvariants(mock_nested)
self.assertInWithGeneratorInvariants(self.resource_a)
self.assertInWithGeneratorInvariants(self.resource_b)
self.raiseTestException()
self.assertRaises(RuntimeError, shouldThrow)
self.assertAfterWithManagerInvariantsWithError(cm_a)
self.assertAfterWithManagerInvariantsWithError(cm_b)
self.assertAfterWithManagerInvariantsWithError(mock_nested)
self.assertAfterWithGeneratorInvariantsWithError(self.resource_a)
self.assertAfterWithGeneratorInvariantsWithError(self.resource_b)
def testNestedExceptionBeforeInnerStatement(self):
mock_a = mock_contextmanager_generator()
mock_b = mock_contextmanager_generator()
self.bar = None
def shouldThrow():
with mock_a as self.foo:
self.assertInWithManagerInvariants(mock_a)
self.assertInWithGeneratorInvariants(self.foo)
self.raiseTestException()
with mock_b as self.bar:
pass
self.assertRaises(RuntimeError, shouldThrow)
self.assertAfterWithManagerInvariantsWithError(mock_a)
self.assertAfterWithGeneratorInvariantsWithError(self.foo)
# The inner statement stuff should never have been touched
self.assertEqual(self.bar, None)
self.assertFalse(mock_b.enter_called)
self.assertFalse(mock_b.exit_called)
self.assertEqual(mock_b.exit_args, None)
def testNestedExceptionAfterInnerStatement(self):
mock_a = mock_contextmanager_generator()
mock_b = mock_contextmanager_generator()
def shouldThrow():
with mock_a as self.foo:
with mock_b as self.bar:
self.assertInWithManagerInvariants(mock_a)
self.assertInWithManagerInvariants(mock_b)
self.assertInWithGeneratorInvariants(self.foo)
self.assertInWithGeneratorInvariants(self.bar)
self.raiseTestException()
self.assertRaises(RuntimeError, shouldThrow)
self.assertAfterWithManagerInvariantsWithError(mock_a)
self.assertAfterWithManagerInvariantsNoError(mock_b)
self.assertAfterWithGeneratorInvariantsWithError(self.foo)
self.assertAfterWithGeneratorInvariantsNoError(self.bar)
def testRaisedStopIteration1(self):
# From bug 1462485
@contextmanager
def cm():
yield
def shouldThrow():
with cm():
raise StopIteration("from with")
with self.assertRaisesRegex(StopIteration, 'from with'):
shouldThrow()
def testRaisedStopIteration2(self):
# From bug 1462485
class cm(object):
def __enter__(self):
pass
def __exit__(self, type, value, traceback):
pass
def shouldThrow():
with cm():
raise StopIteration("from with")
with self.assertRaisesRegex(StopIteration, 'from with'):
shouldThrow()
def testRaisedStopIteration3(self):
# Another variant where the exception hasn't been instantiated
# From bug 1705170
@contextmanager
def cm():
yield
def shouldThrow():
with cm():
raise next(iter([]))
with self.assertRaises(StopIteration):
shouldThrow()
def testRaisedGeneratorExit1(self):
# From bug 1462485
@contextmanager
def cm():
yield
def shouldThrow():
with cm():
raise GeneratorExit("from with")
self.assertRaises(GeneratorExit, shouldThrow)
def testRaisedGeneratorExit2(self):
# From bug 1462485
class cm (object):
def __enter__(self):
pass
def __exit__(self, type, value, traceback):
pass
def shouldThrow():
with cm():
raise GeneratorExit("from with")
self.assertRaises(GeneratorExit, shouldThrow)
def testErrorsInBool(self):
# issue4589: __exit__ return code may raise an exception
# when looking at its truth value.
class cm(object):
def __init__(self, bool_conversion):
class Bool:
def __bool__(self):
return bool_conversion()
self.exit_result = Bool()
def __enter__(self):
return 3
def __exit__(self, a, b, c):
return self.exit_result
def trueAsBool():
with cm(lambda: True):
self.fail("Should NOT see this")
trueAsBool()
def falseAsBool():
with cm(lambda: False):
self.fail("Should raise")
self.assertRaises(AssertionError, falseAsBool)
def failAsBool():
with cm(lambda: 1//0):
self.fail("Should NOT see this")
self.assertRaises(ZeroDivisionError, failAsBool)
class NonLocalFlowControlTestCase(unittest.TestCase):
def testWithBreak(self):
counter = 0
while True:
counter += 1
with mock_contextmanager_generator():
counter += 10
break
counter += 100 # Not reached
self.assertEqual(counter, 11)
def testWithContinue(self):
counter = 0
while True:
counter += 1
if counter > 2:
break
with mock_contextmanager_generator():
counter += 10
continue
counter += 100 # Not reached
self.assertEqual(counter, 12)
def testWithReturn(self):
def foo():
counter = 0
while True:
counter += 1
with mock_contextmanager_generator():
counter += 10
return counter
counter += 100 # Not reached
self.assertEqual(foo(), 11)
def testWithYield(self):
def gen():
with mock_contextmanager_generator():
yield 12
yield 13
x = list(gen())
self.assertEqual(x, [12, 13])
def testWithRaise(self):
counter = 0
try:
counter += 1
with mock_contextmanager_generator():
counter += 10
raise RuntimeError
counter += 100 # Not reached
except RuntimeError:
self.assertEqual(counter, 11)
else:
self.fail("Didn't raise RuntimeError")
class AssignmentTargetTestCase(unittest.TestCase):
def testSingleComplexTarget(self):
targets = {1: [0, 1, 2]}
with mock_contextmanager_generator() as targets[1][0]:
self.assertEqual(list(targets.keys()), [1])
self.assertEqual(targets[1][0].__class__, MockResource)
with mock_contextmanager_generator() as list(targets.values())[0][1]:
self.assertEqual(list(targets.keys()), [1])
self.assertEqual(targets[1][1].__class__, MockResource)
with mock_contextmanager_generator() as targets[2]:
keys = list(targets.keys())
keys.sort()
self.assertEqual(keys, [1, 2])
class C: pass
blah = C()
with mock_contextmanager_generator() as blah.foo:
self.assertEqual(hasattr(blah, "foo"), True)
def testMultipleComplexTargets(self):
class C:
def __enter__(self): return 1, 2, 3
def __exit__(self, t, v, tb): pass
targets = {1: [0, 1, 2]}
with C() as (targets[1][0], targets[1][1], targets[1][2]):
self.assertEqual(targets, {1: [1, 2, 3]})
with C() as (list(targets.values())[0][2], list(targets.values())[0][1], list(targets.values())[0][0]):
self.assertEqual(targets, {1: [3, 2, 1]})
with C() as (targets[1], targets[2], targets[3]):
self.assertEqual(targets, {1: 1, 2: 2, 3: 3})
class B: pass
blah = B()
with C() as (blah.one, blah.two, blah.three):
self.assertEqual(blah.one, 1)
self.assertEqual(blah.two, 2)
self.assertEqual(blah.three, 3)
def testWithExtendedTargets(self):
with nullcontext(range(1, 5)) as (a, *b, c):
self.assertEqual(a, 1)
self.assertEqual(b, [2, 3])
self.assertEqual(c, 4)
class ExitSwallowsExceptionTestCase(unittest.TestCase):
def testExitTrueSwallowsException(self):
class AfricanSwallow:
def __enter__(self): pass
def __exit__(self, t, v, tb): return True
try:
with AfricanSwallow():
1/0
except ZeroDivisionError:
self.fail("ZeroDivisionError should have been swallowed")
def testExitFalseDoesntSwallowException(self):
class EuropeanSwallow:
def __enter__(self): pass
def __exit__(self, t, v, tb): return False
try:
with EuropeanSwallow():
1/0
except ZeroDivisionError:
pass
else:
self.fail("ZeroDivisionError should have been raised")
class NestedWith(unittest.TestCase):
class Dummy(object):
def __init__(self, value=None, gobble=False):
if value is None:
value = self
self.value = value
self.gobble = gobble
self.enter_called = False
self.exit_called = False
def __enter__(self):
self.enter_called = True
return self.value
def __exit__(self, *exc_info):
self.exit_called = True
self.exc_info = exc_info
if self.gobble:
return True
class InitRaises(object):
def __init__(self): raise RuntimeError()
class EnterRaises(object):
def __enter__(self): raise RuntimeError()
def __exit__(self, *exc_info): pass
class ExitRaises(object):
def __enter__(self): pass
def __exit__(self, *exc_info): raise RuntimeError()
def testNoExceptions(self):
with self.Dummy() as a, self.Dummy() as b:
self.assertTrue(a.enter_called)
self.assertTrue(b.enter_called)
self.assertTrue(a.exit_called)
self.assertTrue(b.exit_called)
def testExceptionInExprList(self):
try:
with self.Dummy() as a, self.InitRaises():
pass
except RuntimeError:
pass
self.assertTrue(a.enter_called)
self.assertTrue(a.exit_called)
def testExceptionInEnter(self):
try:
with self.Dummy() as a, self.EnterRaises():
self.fail('body of bad with executed')
except RuntimeError:
pass
else:
self.fail('RuntimeError not reraised')
self.assertTrue(a.enter_called)
self.assertTrue(a.exit_called)
def testExceptionInExit(self):
body_executed = False
with self.Dummy(gobble=True) as a, self.ExitRaises():
body_executed = True
self.assertTrue(a.enter_called)
self.assertTrue(a.exit_called)
self.assertTrue(body_executed)
self.assertNotEqual(a.exc_info[0], None)
def testEnterReturnsTuple(self):
with self.Dummy(value=(1,2)) as (a1, a2), \
self.Dummy(value=(10, 20)) as (b1, b2):
self.assertEqual(1, a1)
self.assertEqual(2, a2)
self.assertEqual(10, b1)
self.assertEqual(20, b2)
def testExceptionLocation(self):
# The location of an exception raised from
# __init__, __enter__ or __exit__ of a context
# manager should be just the context manager expression,
# pinpointing the precise context manager in case there
# is more than one.
def init_raises():
try:
with self.Dummy(), self.InitRaises() as cm, self.Dummy() as d:
pass
except Exception as e:
return e
def enter_raises():
try:
with self.EnterRaises(), self.Dummy() as d:
pass
except Exception as e:
return e
def exit_raises():
try:
with self.ExitRaises(), self.Dummy() as d:
pass
except Exception as e:
return e
for func, expected in [(init_raises, "self.InitRaises()"),
(enter_raises, "self.EnterRaises()"),
(exit_raises, "self.ExitRaises()"),
]:
with self.subTest(func):
exc = func()
f = traceback.extract_tb(exc.__traceback__)[0]
indent = 16
co = func.__code__
self.assertEqual(f.lineno, co.co_firstlineno + 2)
self.assertEqual(f.end_lineno, co.co_firstlineno + 2)
self.assertEqual(f.line[f.colno - indent : f.end_colno - indent],
expected)
if __name__ == '__main__':
unittest.main()
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