Med venlig hilsen:
Hans Larsen
Galgebakken Sønder 4-11A
DK-2620 Albertslund
Danmark/Danio
I has found a bug in Python3.3 on Windows!
Why are all 3 try-statements equal?
I don’t see a “..During handling of above exception, another exception occured: ...”
Where is the bug!
I use Windows 7 64bit!

Please could you give a coherent description of the behaviour you think is a bug.  Include:  (1) what you did, (2) what results you got (including tracebacks for exceptions), (3) what results you expected to get.

Here's the contents of the .rtf file:

PythonWin 3.3.0 (v3.3.0:bd8afb90ebf2, Sep 29 2012, 10:57:17) [MSC v.1600 64 bit (AMD64)] on win32.
Portions Copyright 1994-2008 Mark Hammond - see 'Help/About PythonWin' for further copyright information.
try:
... 	1/0
... except ZeroDivisionError as exp:
... 	raise TypeError('Divided by 0')
... 
Traceback (most recent call last):
  File "<interactive input>", line 4, in <module>
TypeError: Divided by 0
try:
... 	1/0
... except ZeroDivisionError as exp:
... 	raise TypeError('Divided by 0') from exp
... 
Traceback (most recent call last):
  File "<interactive input>", line 4, in <module>
TypeError: Divided by 0
try:
... 	1/0
... except ZeroDivisionError:
... 	raise TypeError('Divided by 0') from None
... 
Traceback (most recent call last):
  File "<interactive input>", line 4, in <module>
TypeError: Divided by 0

Also, please report bugs in English.
(read the devguide to learn more)

That looks like a bug/missing feature in PythonWin to me, which doesn't print __context__ properly. Note: I haven't tested PythonWin to confirm.

Hans: is the output also incorrect in IDLE, or a command line shell? If no, then this isn't a bug in Python itself, but one in PythonWin. You can find the bug tracker at 

http://sourceforge.net/projects/pywin32/

Ramchandra: the bug report actually *is* in English, starting with "I has found ...". The first part is just Hans' postal address (which we don't really need here, but it doesn't hurt having it, either).

-----Oprindelig meddelelse----- 
From: Martin v. Löwis
Sent: Saturday, November 17, 2012 2:45 PM
To: jocjo@mail.dk
Subject: [issue16491] try-except-raise-bug

Martin v. Löwis added the comment:

That looks like a bug/missing feature in PythonWin to me, which doesn't 
print __context__ properly. Note: I haven't tested PythonWin to confirm.

Hans: is the output also incorrect in IDLE, or a command line shell? If no, 
then this isn't a bug in Python itself, but one in PythonWin. You can find 
the bug tracker at

http://sourceforge.net/projects/pywin32/

Ramchandra: the bug report actually *is* in English, starting with "I has 
found ...". The first part is just Hans' postal address (which we don't 
really need here, but it doesn't hurt having it, either).

I have tried it in Python IDLE, but it's the samme except that returns a 
TypeError instead!
----------
nosy: +loewis

_______________________________________
Python tracker <report@bugs.python.org>
<http://bugs.python.org/issue16491>
_______________________________________

Can you paste the traceback you get with IDLE and also try the same from the command line?

I marked this as 3.3+ bug because double reporting is new in 3.x and 'from None' is new in 3.3 (it causes a TypeError in the raise statement ;-).

Command prompt output appears 'correct' (as intended).
[I added blank lines before each try: for reading ease]

Python 3.3.0 (v3.3.0:bd8afb90ebf2, Sep 29 2012, 10:57:17)
 [MSC v.1600 64 bit (AMD64)] on win32

>>> try:
...     1/0
... except ZeroDivisionError as exp:
...     raise TypeError('Divided by 0')
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
TypeError: Divided by 0

>>> try:
...     1/0
... except ZeroDivisionError as exp:
...     raise TypeError('Divided by 0') from exp
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
ZeroDivisionError: division by zero

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
TypeError: Divided by 0

>>> try:
...     1/0
... except ZeroDivisionError as exp:
...     raise TypeError('Divided by 0') from None
...
Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
TypeError: Divided by 0

---------------------------------------------------
In IDLE on Win 7 64, all three give
Traceback (most recent call last):
  File "F:\Python\mypy\tem.py", line 4, in <module>
    raise TypeError('Divided by 0')  # except for change here
TypeError: Divided by 0

We need to see non-Windows IDLE output to see if problem is limited to running with pythonw. Here is copy-paste code.

try:
    1/0
except ZeroDivisionError as exp:
    raise TypeError('Divided by 0') from None

On Linux the result is the same.

The bug is somewhere in print_exception() function in Lib/idlelib/run.py.

Here is a patch.

If no one objects I will commit this next year.

New changeset f28aff31900a by Serhiy Storchaka in branch '3.2':
Issue #16491: IDLE now prints chained exception tracebacks.
http://hg.python.org/cpython/rev/f28aff31900a

New changeset 3feead75c7a5 by Serhiy Storchaka in branch '3.3':
Issue #16491: IDLE now prints chained exception tracebacks.
http://hg.python.org/cpython/rev/3feead75c7a5

New changeset 0793d68a0eba by Serhiy Storchaka in branch 'default':
Issue #16491: IDLE now prints chained exception tracebacks.
http://hg.python.org/cpython/rev/0793d68a0eba

Fixed. Thank you for report, Hans.