Re: Close as Many Files/External resourcs as possible in the face of exceptions

2011-11-21 Thread Vincent Vande Vyvre 


  
  
Le 21/11/11 06:46, GZ a crit:

  Hi,

Here is my situation. A parent object owns a list of files (or other
objects with a close() method). The close() method can sometimes fail
and raise an exception. When the parent object's close() method is
called, it needs to close down as many files it owns as possible, even
if the close() function of some files fail. I also want to re-raise at
least one of the original exceptions so that the outer program can
handle it.

What I come up is something like this, suppose L is a list that holds
all the file objects.

is_closed = set()
try:
for f in L:
f.close()
is_closed.add(f)
except:
try:
raise #re-raise immediately, keeping context intact
finally:
for f in L: # close the rest of the file objects
if f not in is_closed:
 try:
 f.close()
 except:
  pass

It will re-raise the first exception and preserve the context and
close as many other files as possible while ignoring any further
exceptions.

But this looks really awkward. And in the case that two files fail to
close, I am not sure the best strategy is to ignore the second
failure.

What is a better way of handling such situation?

Thanks,
gz



Not tested

def close_all(L):
 is_not_closed = {}
 def close_(obj):
  try:
   obj.close()
  except Exception, why
   is_not_closed[obj] = why
 
 for f in L:
  close_(f)

Now, your dictionnary contain the file as key and the exception
message as value.

-- 
  Vincent V.V.
  Oqapy . Qarte+7 . PaQager
  


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Re: Close as Many Files/External resourcs as possible in the face of exceptions

2011-11-21 Thread Mel Wilson 
GZ wrote:
 Here is my situation. A parent object owns a list of files (or other
 objects with a close() method). The close() method can sometimes 
fail
 and raise an exception. When the parent object's close() method is
 called, it needs to close down as many files it owns as possible, 
even
 if the close() function of some files fail. I also want to re-raise 
at
 least one of the original exceptions so that the outer program can
 handle it.
[ ... ]
 
 It will re-raise the first exception and preserve the context and
 close as many other files as possible while ignoring any further
 exceptions.
 
 But this looks really awkward. And in the case that two files fail 
to
 close, I am not sure the best strategy is to ignore the second
 failure.

I imagine you could save any caught exception instances in a list and 
study them later.

Mel.

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Re: Close as Many Files/External resourcs as possible in the face of exceptions

2011-11-21 Thread Terry Reedy 

On 11/21/2011 7:09 AM, Mel Wilson wrote:

GZ wrote:

Here is my situation. A parent object owns a list of files (or other
objects with a close() method). The close() method can sometimes fail
and raise an exception. When the parent object's close() method is
called, it needs to close down as many files it owns as possible, even
if the close() function of some files fail. I also want to re-raise at
least one of the original exceptions so that the outer program can
handle it.

[ ... ]


It will re-raise the first exception and preserve the context and
close as many other files as possible while ignoring any further
exceptions.

But this looks really awkward. And in the case that two files fail to
close, I am not sure the best strategy is to ignore the second failure.


I imagine you could save any caught exception instances in a list and
study them later.


Yes, I would raise a custom exception instance that takes such a list of 
failures in its constructor. Give it a custom __str__ method to display 
them all.


--
Terry Jan Reedy

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Close as Many Files/External resourcs as possible in the face of exceptions

2011-11-20 Thread GZ 
Hi,

Here is my situation. A parent object owns a list of files (or other
objects with a close() method). The close() method can sometimes fail
and raise an exception. When the parent object's close() method is
called, it needs to close down as many files it owns as possible, even
if the close() function of some files fail. I also want to re-raise at
least one of the original exceptions so that the outer program can
handle it.

What I come up is something like this, suppose L is a list that holds
all the file objects.

is_closed = set()
try:
for f in L:
f.close()
is_closed.add(f)
except:
try:
raise #re-raise immediately, keeping context intact
finally:
for f in L: # close the rest of the file objects
if f not in is_closed:
 try:
 f.close()
 except:
  pass

It will re-raise the first exception and preserve the context and
close as many other files as possible while ignoring any further
exceptions.

But this looks really awkward. And in the case that two files fail to
close, I am not sure the best strategy is to ignore the second
failure.

What is a better way of handling such situation?

Thanks,
gz

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