Q on explicitly calling file.close

[Dave Angel]

kj wrote:
> There's something wonderfully clear about code like this:
>
>     # (1)
>     def spam(filename):
>         for line in file(filename):
>             do_something_with(line)
>
> It is indeed pseudo-codely beautiful.  But I gather that it is not
> correct to do this, and that instead one should do something like
>
>     # (2)
>     def spam(filename):
>         fh = file(filename)
>         try:
>             for line in fh:
>                 do_something_with(line)
>         finally:
>             fh.close()
>
> ...or alternatively, if the with-statement is available:
>
>     # (3)
>     def spam(filename):
>         with file(filename) as fh:
>             for line in fh:
>                 do_something_with(line)
>
> Mind you, (3) is almost as simple as (1) (only one additional line),
> but somehow it lacks (1)'s direct simplicity.  (And it adds one
> more indentation level, which I find annoying.)  Furthermore, I
> don't recall ever coming across either (2) or (3) "in the wild",
> even after reading a lot of high-quality Python code (e.g. standard
> library modules).
>
> Finally, I was under the impression that Python closed filehandles
> automatically when they were garbage-collected.  (In fact (3)
> suggests as much, since it does not include an implicit call to
> fh.close.) If so, the difference between (1) and (3) does not seem
> very big.  What am I missing here?
>
> kynn
>
>   
We have to distinguish between reference counted and garbage collected.  
As MRAB says, when the reference count goes to zero, the file is 
immediately closed, in CPython implementation.  So all three are 
equivalent on that platform.

But if you're not sure the code will run on CPython, then you have to 
have something that explicitly catches the out-of-scopeness of the file 
object.  Both your (2) and (3) do that, with different syntaxes.

DaveA