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unittest: optimise for code size and memory use #1125

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da49706
unittest: Optimise by reusing AssertRaisesContext for assertWarns.
dpgeorge Jun 25, 2026
43d1ea1
unittest: Optimise by removing support for CPython.
dpgeorge Jun 25, 2026
42cb162
unittest: Optimise calling of _handle_test_exception.
dpgeorge Jun 25, 2026
cb3c655
unittest: Optimise by only formatting msg if needed.
dpgeorge Jun 25, 2026
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139 changes: 65 additions & 74 deletions python-stdlib/unittest/unittest/__init__.py
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Original file line number Diff line number Diff line change
@@ -1,11 +1,6 @@
import io
import sys

try:
import traceback
except ImportError:
traceback = None


class SkipTest(Exception):
pass
Expand All @@ -19,9 +14,12 @@ def __enter__(self):
return self

def __exit__(self, exc_type, exc_value, tb):
if self.expected is None:
# Used by assertWarns, do nothing.
return
self.exception = exc_value
if exc_type is None:
assert False, "%r not raised" % self.expected
raise AssertionError("%r not raised" % self.expected)
if issubclass(exc_type, self.expected):
# store exception for later retrieval
self.exception = exc_value
Expand All @@ -42,8 +40,8 @@ def __init__(self, msg=None, params=None):
def __enter__(self):
pass

def __exit__(self, *exc_info):
if exc_info[0] is not None:
def __exit__(self, exc_type, exc_value, tb):
if exc_type is not None:
# Exception raised
global __test_result__, __current_test__
test_details = __current_test__
Expand All @@ -53,19 +51,11 @@ def __exit__(self, *exc_info):
detail = ", ".join("%s=%s" % k_v for k_v in self.params.items())
test_details += (" (%s)" % detail,)

_handle_test_exception(test_details, __test_result__, exc_info, False)
_handle_test_exception(test_details, __test_result__, exc_value, False)
# Suppress the exception as we've captured it above
return True


class NullContext:
def __enter__(self):
pass

def __exit__(self, exc_type, exc_value, traceback):
pass


class TestCase:
def __init__(self):
pass
Expand All @@ -88,27 +78,31 @@ def skipTest(self, reason):
raise SkipTest(reason)

def fail(self, msg=""):
assert False, msg
raise AssertionError(msg)

def assertEqual(self, x, y, msg=""):
if not msg:
msg = "%r vs (expected) %r" % (x, y)
assert x == y, msg
if not x == y:
if not msg:
msg = "%r vs (expected) %r" % (x, y)
raise AssertionError(msg)

def assertNotEqual(self, x, y, msg=""):
if not msg:
msg = "%r not expected to be equal %r" % (x, y)
assert x != y, msg
if not x != y:
if not msg:
msg = "%r not expected to be equal %r" % (x, y)
raise AssertionError(msg)

def assertLessEqual(self, x, y, msg=None):
if msg is None:
msg = "%r is expected to be <= %r" % (x, y)
assert x <= y, msg
if not x <= y:
if msg is None:
msg = "%r is expected to be <= %r" % (x, y)
raise AssertionError(msg)

def assertGreaterEqual(self, x, y, msg=None):
if msg is None:
msg = "%r is expected to be >= %r" % (x, y)
assert x >= y, msg
if not x >= y:
if msg is None:
msg = "%r is expected to be >= %r" % (x, y)
raise AssertionError(msg)

def assertAlmostEqual(self, x, y, places=None, msg="", delta=None):
if x == y:
Expand All @@ -129,7 +123,7 @@ def assertAlmostEqual(self, x, y, places=None, msg="", delta=None):
if not msg:
msg = "%r != %r within %r places" % (x, y, places)

assert False, msg
raise AssertionError(msg)

def assertNotAlmostEqual(self, x, y, places=None, msg="", delta=None):
if delta is not None and places is not None:
Expand All @@ -148,45 +142,53 @@ def assertNotAlmostEqual(self, x, y, places=None, msg="", delta=None):
if not msg:
msg = "%r == %r within %r places" % (x, y, places)

assert False, msg
raise AssertionError(msg)

def assertIs(self, x, y, msg=""):
if not msg:
msg = "%r is not %r" % (x, y)
assert x is y, msg
if not x is y:
if not msg:
msg = "%r is not %r" % (x, y)
raise AssertionError(msg)

def assertIsNot(self, x, y, msg=""):
if not msg:
msg = "%r is %r" % (x, y)
assert x is not y, msg
if not x is not y:
if not msg:
msg = "%r is %r" % (x, y)
raise AssertionError(msg)

def assertIsNone(self, x, msg=""):
if not msg:
msg = "%r is not None" % x
assert x is None, msg
if not x is None:
if not msg:
msg = "%r is not None" % x
raise AssertionError(msg)

def assertIsNotNone(self, x, msg=""):
if not msg:
msg = "%r is None" % x
assert x is not None, msg
if not x is not None:
if not msg:
msg = "%r is None" % x
raise AssertionError(msg)

def assertTrue(self, x, msg=""):
if not msg:
msg = "Expected %r to be True" % x
assert x, msg
if not x:
if not msg:
msg = "Expected %r to be True" % x
raise AssertionError(msg)

def assertFalse(self, x, msg=""):
if not msg:
msg = "Expected %r to be False" % x
assert not x, msg
if x:
if not msg:
msg = "Expected %r to be False" % x
raise AssertionError(msg)

def assertIn(self, x, y, msg=""):
if not msg:
msg = "Expected %r to be in %r" % (x, y)
assert x in y, msg
if not x in y:
if not msg:
msg = "Expected %r to be in %r" % (x, y)
raise AssertionError(msg)

def assertIsInstance(self, x, y, msg=""):
assert isinstance(x, y), msg
if not isinstance(x, y):
raise AssertionError(msg)

def assertRaises(self, exc, func=None, *args, **kwargs):
if func is None:
Expand All @@ -199,10 +201,10 @@ def assertRaises(self, exc, func=None, *args, **kwargs):
return
raise e

assert False, "%r not raised" % exc
raise AssertionError("%r not raised" % exc)

def assertWarns(self, warn):
return NullContext()
return AssertRaisesContext(None)


def skip(msg):
Expand Down Expand Up @@ -235,7 +237,7 @@ def test_exp_fail(*args, **kwargs):
except:
pass
else:
assert False, "unexpected success"
raise AssertionError("unexpected success")

return test_exp_fail

Expand Down Expand Up @@ -332,28 +334,19 @@ def __add__(self, other):
return self


def _capture_exc(exc, exc_traceback):
buf = io.StringIO()
if hasattr(sys, "print_exception"):
sys.print_exception(exc, buf)
elif traceback is not None:
traceback.print_exception(None, exc, exc_traceback, file=buf)
return buf.getvalue()


def _handle_test_exception(
current_test: tuple, test_result: TestResult, exc_info: tuple, verbose=True
current_test: tuple, test_result: TestResult, exc: Exception, verbose=True
):
exc = exc_info[1]
traceback = exc_info[2]
ex_str = _capture_exc(exc, traceback)
if isinstance(exc, SkipTest):
reason = exc.args[0]
test_result.skippedNum += 1
test_result.skipped.append((current_test, reason))
print(" skipped:", reason)
return
elif isinstance(exc, AssertionError):
buf = io.StringIO()
sys.print_exception(exc, buf)
ex_str = buf.getvalue()
if isinstance(exc, AssertionError):
test_result.failuresNum += 1
test_result.failures.append((current_test, ex_str))
if verbose:
Expand Down Expand Up @@ -402,9 +395,7 @@ def run_one(test_function):
else:
print(" ok")
except Exception as ex:
_handle_test_exception(
current_test=(name, c), test_result=test_result, exc_info=(type(ex), ex, None)
)
_handle_test_exception((name, c), test_result, ex)
# Uncomment to investigate failure in detail
# raise ex
finally:
Expand Down
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