[Tutor] reading lines from a list of files

[Alex Kleider]

On 2015-05-14 00:01, Alan Gauld wrote:
> On 14/05/15 06:27, Alex Kleider wrote:
> 
>> The following seems to work-
>> 
>>      for f_name in list_of_file_names:
>>          for line in open(f_name, 'r'):
>>              process(line)
>> 
>> but should I be worried that the file doesn't get explicitly closed?
> 
> If you are only ever reading from the file then no, I'd not worry
> too much. But in the general case, where you might be making
> changes then yes, you should worry.
> 
> It will work 99% of the time but if things go wrong there's always
> a chance that a file has not been closed yet and your changes have
> not been written to the file. But if you are not changing the file
> it doesn't matter too much.
> 
> The only other consideration is that some OS might put a lock
> on the file even if it's only read access, so in those cases
> closing will release the lock sooner. But I don't think any of
> the popular OS do that any more.

Thank you, Alan; I hadn't appreciated the important difference in risk
with write vs read.  It's clear that 'best practice' would be to use
'with' so as to 'cover all bases.'