Exception context issue

[slozier]

The meaning of "handling an exception" in sys.exc_info changed in Python 3. It changed from (see https://docs.python.org/3/library/sys.html#sys.exc_info):

executing or having executed an except clause

to:

executing an except clause

Because of this change the tracebacks may return incorrect outputs, for example:

def test4():
    try:
        raise Exception(1)
    except:
        pass    
    raise Exception(2)

test4()

outputs (we should only see the Exception: 2 traceback):

Traceback (most recent call last):
  File "<stdin>", line 3, in test4
Exception: 1

During handing of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 6, in test4
Exception: 2

Here are a few test cases which should all pass:

import sys

def test1():
    try:
        raise Exception
    except:
        pass
    assert sys.exc_info() == (None, None, None)

def test2():
    def gen():
        try:
            raise Exception
        except:
            exc_info = sys.exc_info()
            yield exc_info
            yield sys.exc_info()
        yield sys.exc_info()
    x = gen()
    exc_info = next(x)
    assert sys.exc_info() == (None, None, None)
    assert next(x) == exc_info
    assert next(x) == (None, None, None)

def test3():
    try:
        try:
            raise Exception(1)
        except:
            pass    
        raise Exception(2)
    except Exception as e:
        assert e.__context__ is None

test1()
test2()
test3()