[ python-Bugs-411881 ] Use of "except:" in modules
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Thu Dec 11 15:54:47 EST 2003
Bugs item #411881, was opened at 2001-03-28 07:58
Message generated for change (Comment added) made by gvanrossum
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Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 2
Submitted By: Itamar Shtull-Trauring (itamar)
Assigned to: Skip Montanaro (montanaro)
Summary: Use of "except:" in modules
Initial Comment:
A large amount of modules in the standard library use
"except:" instead of specifying the exceptions to be
caught. In some cases this may be correct, but I think
in most cases this not true and this may cause
problems. Here's the list of modules, which I got by
doing:
grep "except:" *.py | cut -f 1 -d " " | sort | uniq
Bastion.py
CGIHTTPServer.py
Cookie.py
SocketServer.py
anydbm.py
asyncore.py
bdb.py
cgi.py
chunk.py
cmd.py
code.py
compileall.py
doctest.py
fileinput.py
formatter.py
getpass.py
htmllib.py
imaplib.py
inspect.py
locale.py
locale.py
mailcap.py
mhlib.py
mimetools.py
mimify.py
os.py
pdb.py
popen2.py
posixfile.py
pre.py
pstats.py
pty.py
pyclbr.py
pydoc.py
repr.py
rexec.py
rfc822.py
shelve.py
shutil.py
tempfile.py
threading.py
traceback.py
types.py
unittest.py
urllib.py
zipfile.py
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>Comment By: Guido van Rossum (gvanrossum)
Date: 2003-12-11 15:54
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You're right. The logging module uses more blank except:
clauses than I'm comfortable with. Anyone want to upload a
patch set?
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Comment By: Grant Monroe (gmonroe)
Date: 2003-12-11 15:50
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A good example of an incorrect use of a blanket "except:"
clause is in __init__.py in the logging module. The emit
method of the StreamHandler class should special case
KeyboardInterrupt. Something like this:
try:
....
except KeyboardInterrupt:
raise
except:
self.handleError(record)
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Comment By: Raymond Hettinger (rhettinger)
Date: 2003-09-01 22:47
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Some efforts were made to remove many bare excepts prior
to Py2.3a1. Briefly scanning those that remain, it looks like
many of them are appropriate or best left alone.
I recommend that this bug be closed unless someone sees
something specific that demands a change.
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Comment By: Brett Cannon (bcannon)
Date: 2003-05-16 19:30
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threading.py is clear. It's blanket exceptions are for printing debug output
since exceptions in threads don't get passed back to the original frame
anyway.
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Comment By: Skip Montanaro (montanaro)
Date: 2002-08-13 23:15
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checked in fileinput.py (v 1.15) with three except:'s tightened up. The
comment in the code about IOError notwithstanding, I don't see how any
of the three situations would have caught anything other than OSError.
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Comment By: Skip Montanaro (montanaro)
Date: 2002-08-12 15:58
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Note that this particular item was expected to be an ongoing item, with
no obvious closure. Some of the bare excepts will have subtle
ramifications, and it's not always obvious what specific exceptions
should be caught. I've made a few changes to my local source tree
which I should check in.
Rather than opening new tracker items, I believe those with checkin
privileges should correct those flaws they identify and attach a comment
which will alert those monitoring the item. Those people without checkin
privileges should just attach a patch with a note.
Skip
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Comment By: Martin v. Löwis (loewis)
Date: 2002-08-12 03:22
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My proposal would be to track this under a different issue:
Terry, if you volunteer, please produce a new list of
offenders (perhaps in an attachment to the report so it can
be updated), and attach any fixes that you have to that report.
People with CVS write access can then apply those patches
and delete them from the report.
If you do so, please post the new issue number in this
report, so we have a link.
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Comment By: Terry J. Reedy (tjreedy)
Date: 2002-08-11 14:16
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Remove types.py from the list. As distributed with 2.2.1, it
has 5 'except xxxError:' statements but no offending bare
except:'s.
Skip (or anyone else): if/when you pursue this, I volunteer
to do occasional sleuthing and send reports with
suggestions and/or questions. Example: getpass.py has
one 'offense':
try:
fd = sys.stdin.fileno()
except:
return default_getpass(prompt)
According to lib doc 2.2.8 File Objects (as I interpret) fileno
() should either work without exception or *not* be
implemented. Suggestion: insert AttributeError . Question:
do we protect against pseudofile objects that ignore doc
and have fake .fileno() that raises NotImplementedError or
whatever?
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Comment By: Skip Montanaro (montanaro)
Date: 2002-03-23 01:02
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as partial fix, checked in changes for the following
modules:
mimetools.py (1.24)
popen2.py (1.23)
quopripy (1.19)
CGIHTTPServer.py (1.22)
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Comment By: Skip Montanaro (montanaro)
Date: 2002-03-20 16:24
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Here is a context diff with proposed changes for the
following modules: CGIHTTPServer, cgi, cmd, code,
fileinput, httplib, inspect, locale, mimetools, popen2,
quopri
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Comment By: Martin v. Löwis (loewis)
Date: 2001-08-11 11:06
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Fixed urllib in 1.131 and types in 1.19.
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Comment By: Fred L. Drake, Jr. (fdrake)
Date: 2001-07-04 03:11
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Fixed modules mhlib and rfc822 (SF is having a problem
generating the checkin emails, though).
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Comment By: Fred L. Drake, Jr. (fdrake)
Date: 2001-05-11 15:40
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OK, I've fixed up a few more modules:
anydbm
chunk
formatter
htmllib
mailcap
pre
pty
I made one change to asyncore as well, but other bare except
clauses remain there; I'm not sufficiently familiar with
that code to just go digging into those.
I also fixed an infraction in pstats, but left others for now.
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Comment By: Tim Peters (tim_one)
Date: 2001-04-23 04:14
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Ping's intent is that pydoc work under versions of Python
as early as 1.5.2, so that sys._getframe is off-limits in
pydoc and its supporting code (like inspect.py).
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Comment By: Martin v. Löwis (loewis)
Date: 2001-04-23 03:32
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For inspect.py, why is it necessary to keep the old code at
all? My proposal: remove currentframe altogether, and do
currentframe = sys._getframe
unconditionally.
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Comment By: Itamar Shtull-Trauring (itamar)
Date: 2001-04-22 10:52
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I submitted a 4th patch. I'm starting to run out of easy
cases...
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Comment By: Skip Montanaro (montanaro)
Date: 2001-04-19 05:15
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I believe the following patch is correct for the try/except
in inspect.currentframe. Note that it fixes two problems.
One, it avoids a bare except. Two, it gets rid of a string
argument to the raise statement (string exceptions are now
deprecated, right?).
*** /tmp/skip/inspect.py Thu Apr 19 04:13:36 2001
--- /tmp/skip/inspect.py.~1.16~ Thu Apr 19 04:13:36 2001
***************
*** 643,650 ****
def currentframe():
"""Return the frame object for the caller's stack
frame."""
try:
! 1/0
! except ZeroDivisionError:
return sys.exc_traceback.tb_frame.f_back
if hasattr(sys, '_getframe'): currentframe = sys._getframe
--- 643,650 ----
def currentframe():
"""Return the frame object for the caller's stack
frame."""
try:
! raise 'catch me'
! except:
return sys.exc_traceback.tb_frame.f_back
if hasattr(sys, '_getframe'): currentframe = sys._getframe
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Comment By: Itamar Shtull-Trauring (itamar)
Date: 2001-04-17 11:27
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inspect.py uses sys_getframe if it's there, the other code
is for backwards compatibility.
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Comment By: Guido van Rossum (gvanrossum)
Date: 2001-04-11 13:24
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Actually, inspect.py should use sys._getframe()!
And yes, KeyboardError is definitely one of the reasons why
this is such a bad idiom...
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Comment By: Walter Dörwald (doerwalter)
Date: 2001-04-11 13:15
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> Can you identify modules where catching everything
> is incorrect
If "everything" includes KeyboardInterrupt, it's
definitely incorrect, even in inspect.py's simple
try:
raise 'catch me'
except:
return sys.exc_traceback.tb_frame.f_back
which should probably be:
try:
raise 'catch me'
except KeyboardInterrupt:
raise
except:
return sys.exc_traceback.tb_frame.f_back
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Comment By: Walter Dörwald (doerwalter)
Date: 2001-04-11 13:13
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> Can you identify modules where catching everything
> is incorrect
If "everything" includes KeyboardInterrupt, it's
definitely incorrect, even in inspect.py's simple
try:
raise 'catch me'
except:
return sys.exc_traceback.tb_frame.f_back
which should probably be:
try:
raise 'catch me'
except KeyboardInterrupt:
raise
except:
return sys.exc_traceback.tb_frame.f_back
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Comment By: Guido van Rossum (gvanrossum)
Date: 2001-04-10 11:45
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I've applied the three patches you supplied.
I agree with Martin that to do this right we'll have to
tread carefully. But please go on!
(No way more of this will find its way into 2.1 though.)
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Comment By: Itamar Shtull-Trauring (itamar)
Date: 2001-03-30 05:54
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inspect.py should be removed from this list, the use is
correct.
In general, I just submitted this bug so that when people
are editing a module they'll notice these things, since in
some cases only someone who knows the code very well can
know if the "expect:" is needed or not.
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Comment By: Martin v. Löwis (loewis)
Date: 2001-03-30 01:59
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Can you identify modules where catching everything is
incorrect, and propose changes to correct them. This should
be done one-by-one, with careful analysis in each case, and
may take well months or years to complete.
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