Q on explicitly calling file.close

[Tim Chase]

> CPython uses reference counting, so an object is garbage collected as
> soon as there are no references to it, but that's just an implementation
> detail.
> 
> Other implementations, such as Jython and IronPython, don't use
> reference counting, so you don't know when an object will be garbage
> collected, which means that the file might remain open for an unknown
> time afterwards in case 1 above.
> 
> Most people use CPython, so it's not surprising that case 1 is so
> common.

Additionally, many scripts just use a small number of files (say, 
1-5 files) so having a file-handle open for the duration of the 
run it minimal overhead.

On the other hand, when processing thousands of files, I always 
explicitly close each file to make sure I don't exhaust some 
file-handle limit the OS or interpreter may enforce.

-tkc