New submission from Jim DeLaHunt <from.pyt...@jdlh.com>:
In Python 3.6.5, Task.__repr__() with raise an AssertionError for
certain, arguably incorrect, coroutines which the instantiation of Task()
accepts. repr(task) thus fails with an AssertionError, instead of
returning a string which describes the task object and why its coroutine
is wrong. Complications ensue.
In particular, if this Task is used in a unittest.TestCase, and appears in test
failure diagnostics, the test
diagnostics are discarded when the AssertionError occurs, masking the
problem in the code under test.
In Python 3.7.0, Task.__init__() checks the supplied coroutine argument,
using the same asyncio.iscoroutine() method which Task.__repr__() calls.
Thus, while repr(task) can still raise an AssertionError, it is much harder to
reach this situation. Task.__init__() is likely to raise an exception first,
and the diagnostics will be pretty clear.
To reproduce:
1. Here is a simple, perhaps misguided, attempt at a coroutine, and a Task
which uses it:
import asyncio
async def ag():
yield None
print("type(ag()) is ", type(ag()))
print("asyncio.iscoroutine(ag)? ", asyncio.iscoroutine(ag))
print("repr(ag()) is ", repr(ag()))
task = asyncio.get_event_loop().create_task(ag())
print("type(task) is ", type(task))
print("asyncio.iscoroutine(task._coro)? ", asyncio.iscoroutine(task._coro))
print("repr(task) is ")
print(repr(task))
The output from Python 3.6.5 is:
type(ag()) is <class 'async_generator'>
asyncio.iscoroutine(ag)? False
repr(ag()) is <async_generator object ag at 0x108331938>
type(task) is <class '_asyncio.Task'>
asyncio.iscoroutine(task._coro)? False
repr(task) is
Traceback (most recent call last):
File "bug_task_repr_1.py", line 31, in <module>
print(repr(task))
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/base_tasks.py",
line 15, in _task_repr_info
coro = coroutines._format_coroutine(task._coro)
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/coroutines.py",
line 276, in _format_coroutine
assert iscoroutine(coro)
AssertionError
Observed behaviour:
Here is a unit test which attempts to exercise the above Task. The test fails,
but the AssertionError in Task.__repr__() discards the error diagnostics:
from asyncio import test_utils
class Test(test_utils.TestCase):
def setUp(self):
super().setUp()
self.loop = self.new_test_loop()
def test_wrongly_scheduled(self):
# this is a simple, and maybe mistaken, coroutine
async def ag():
yield None
_ = self.loop.create_task(ag())
test_utils.run_once(self.loop)
The output from Python 3.6.5 is:
% python -m unittest bug_task_repr_2.py
Exception in default exception handler
Traceback (most recent call last):
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/base_events.py",
line 1291, in call_exception_handler
self.default_exception_handler(context)
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/base_events.py",
line 1263, in default_exception_handler
value = repr(value)
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/base_tasks.py",
line 15, in _task_repr_info
coro = coroutines._format_coroutine(task._coro)
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/coroutines.py",
line 276, in _format_coroutine
assert iscoroutine(coro)
AssertionError
.
----------------------------------------------------------------------
Ran 1 test in 0.001s
OK
Note that the error traceback is all about the exception from Task.__repr__(),
and the diagnostics about why the unit test failed is discarded.
Expected behaviour:
Here is the same unit test, but this time with a replacement method for
Task._task_repr_info() which avoids the AssertionError.
import asyncio
from asyncio import test_utils
import types
class Test(test_utils.TestCase):
def setUp(self):
super().setUp()
self.loop = self.new_test_loop()
def test_wrongly_scheduled(self):
# this is a simple, and maybe mistaken, coroutine
async def ag():
yield None
task = self.loop.create_task(ag())
task._repr_info = types.MethodType( task_safe_repr_info, task )
test_utils.run_once(self.loop)
def task_safe_repr_info(self):
'''task.task_safe_repr_info(): string list representation of task. Won't
raise AssertionError
If you have a Task object which is raising an AssertionError from
"assert iscoroutine(coro)", then assign to instantiated object:
task._repr_info = task_safe_repr_info
Patched task object should be able to survive the AssertionError and
deliver a useful representation.
'''
try:
# from Task._repr_info(self), which calls
base_tasks._task_repr_info(self)
info = asyncio.base_futures._future_repr_info(self)
if self._must_cancel:
# replace status
info[0] = 'cancelling'
# Expand: coro = coroutines._format_coroutine(task._coro)
# coro_repr = coroutines._format_coroutine(task._coro):276 does assert
iscoroutine(coro)
# This fails. Expand that routine, without the assert.
coro = self._coro
if not hasattr(coro, 'cr_code') and not hasattr(coro, 'gi_code'):
# Most likely a built-in type or a Cython coroutine.
# Built-in types might not have __qualname__ or __name__.
coro_name = getattr(
coro, '__qualname__',
getattr(coro, '__name__', type(coro).__name__))
coro_name = '{}()'.format(coro_name)
running = False
try:
running = coro.cr_running
except AttributeError:
try:
running = coro.gi_running
except AttributeError:
pass
if running:
coro_repr = '{} running'.format(coro_name)
else:
coro_repr = coro_name
else:
coro_name = None
if isinstance(coro, asyncio.coroutines.CoroWrapper):
func = coro.func
coro_name = coro.__qualname__
if coro_name is not None:
coro_name = '{}()'.format(coro_name)
else:
func = coro
if coro_name is None:
coro_name = asyncio.events._format_callback(func, (), {})
try:
coro_code = coro.gi_code
except AttributeError:
coro_code = coro.cr_code
try:
coro_frame = coro.gi_frame
except AttributeError:
coro_frame = coro.cr_frame
filename = coro_code.co_filename
lineno = 0
if (isinstance(coro, asyncio.coroutines.CoroWrapper) and
not inspect.isgeneratorfunction(coro.func) and
coro.func is not None):
source = asyncio.events._get_function_source(coro.func)
if source is not None:
filename, lineno = source
if coro_frame is None:
coro_repr = ('%s done, defined at %s:%s'
% (coro_name, filename, lineno))
else:
coro_repr = ('%s running, defined at %s:%s'
% (coro_name, filename, lineno))
elif coro_frame is not None:
lineno = coro_frame.f_lineno
coro_repr = ('%s running at %s:%s'
% (coro_name, filename, lineno))
else:
lineno = coro_code.co_firstlineno
coro_repr = ('%s done, defined at %s:%s'
% (coro_name, filename, lineno))
# end of coroutines._format_coroutine(task._coro)
# return coro_repr
info.insert(1, 'coro=%s(<%s>)' % (type(coro), coro_repr))
if self._fut_waiter is not None:
info.insert(2, 'wait_for=%r' % self._fut_waiter)
return info
except:
return [type(self), id(self)]
Here is the result of running that unit test on the patched Task object. Note
that there is no AssertionError from repr(), and the diagnostics about the
failing unit tests are now clear:
% python -m unittest bug_task_repr_3.py
.
----------------------------------------------------------------------
Ran 1 test in 0.000s
OK
Task exception was never retrieved
future: <Task finished coro=<class
'async_generator'>(<Test.test_wrongly_scheduled.<locals>.ag()>)
exception=AttributeError("'async_generator' object has no attribute 'send'",)>
AttributeError: 'async_generator' object has no attribute 'send'
----------
components: asyncio
messages: 321292
nosy: JDLH, asvetlov, yselivanov
priority: normal
severity: normal
status: open
title: repr(task) raises AssertionError for coros which loop.create_task
accepts; complications ensue
type: crash
versions: Python 3.6
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue34071>
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