[Python-bugs-list] [ python-Bugs-411881 ] Use of "except:" in modules

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Bugs item #411881, was updated on 2001-03-28 04:58
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Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 3
Submitted By: Itamar Shtull-Trauring (itamar)
Assigned to: Nobody/Anonymous (nobody)
>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: Skip Montanaro (montanaro)
Date: 2001-04-19 02:15

Message:
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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 08:27

Message:
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inspect.py uses sys_getframe if it's there, the other code
is for backwards compatibility.

----------------------------------------------------------------------

Comment By: Guido van Rossum (gvanrossum)
Date: 2001-04-11 10:24

Message:
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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 10:15

Message:
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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


----------------------------------------------------------------------

Comment By: Walter Dörwald (doerwalter)
Date: 2001-04-11 10:13

Message:
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user_id=89016

> 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


----------------------------------------------------------------------

Comment By: Guido van Rossum (gvanrossum)
Date: 2001-04-10 08:45

Message:
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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 02:54

Message:
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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.

----------------------------------------------------------------------

Comment By: Martin v. Löwis (loewis)
Date: 2001-03-29 22:59

Message:
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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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