Opening files without closing them

[Bryan]

Peter Hansen wrote:
> 3c273 wrote:
>> "Robert Kern" <robert.kern at gmail.com> wrote in message
>> news:mailman.2794.1141683892.27775.python-list at python.org...
>>
>>> Paul Rubin wrote:
>>>
>>>> Say that the open is inside the try block.  If the file can't be
>>>> opened, then 'open' raises an exception, 'f' doesn't get set, and then
>>>> the 'finally' clause tries to close f.  f might have been previously
>>>> bound to some other file (which still has other handles alive) and so
>>>> the wrong file gets closed.
>>> And even if 'f' wasn't bound to anything, you will get a NameError instead
>> of
>>
>>> the exception that you're really interested in seeing.
>>
>> Thanks to both of you. So in order to be thorough, should I be doing:
>> try:
>>     f=open('file')
>> except: IOError:
>>     print 'doesn't exist'
>>     so_something_else_instead()
>>
>> try:
>>     contents = f.read()
>> finally:
>>     f.close()
> 
> Unfortunately, that would still have trouble if the first exception 
> handler was executed, since then you'd try read from f, which would fail 
> with another exception, and then you'd try to close f, and that would 
> probably fail and raise an exception that isn't caught anywhere.
> 
> So this is better, though probably excessive in small scripts:
> 
> try:
>      f = open('file')
> except IOError:
>      # do something else
> else:
>      try:
>          content = f.read()
>      finally:
>          f.close()
> 
> This takes advantage of "else" on try statements, which executes only if 
> the except statement is not executed.
> 
> -Peter
> 

this is what i always do for files and other types of resources:


if it's a low-level routine, i usually let any exceptions bubble up to a higher 
level routine that cares or knows what to do.

f = open('file')
try:
     # do something
finally:
     f.close()


if i really want to handle the exception, then i handle it at a conceptually 
"higher" level by wrapping it in an exception which is basically what some 
higher-level routine would do anyways.


try:
     f = open('file)
     try:
         # do something
     finally:
         f.close()
except IOError:
     # handle exceptions



bryan