Bug#913274: Changing the _is_real_file() function

[Colin Watson]

On Mon, Dec 31, 2018 at 07:45:52PM +1100, Stuart Prescott wrote:
> Many years ago in doing the Python 2→3 port for python-debian, you wrote a
> function to guard against giving file-like objects that were not file
> handles to apt_pkg [1]. The reason I've been looking at this today is that 
> the current check incorrectly identifies NamedTemporaryFile as not being
> a real file, while apt_pkg is happy to accept such objects.
> 
> I *think* this can now be simplified as in the following commit, presumably
> due to changes to the supported versions of Python we care about:
> 
> https://salsa.debian.org/python-debian-team/python-debian/merge_requests/8/diffs#89edc1b4f3188ea0d56566993279f0a9b5ad7c3a_298_298

Prior to python-apt 0.7.90 (specifically
https://salsa.debian.org/apt-team/python-apt/commit/62d7f4b80d56ef1e27039441cd6584cfb71d6502),
apt_pkg.TagFile only accepted actual file objects.  I think the code in
python-debian that I was porting predated that change, and so did an
isinstance check; I don't remember exactly what I was thinking when I
did the port, but perhaps I didn't follow the history all the way
through, or perhaps I was just trying to make the most conservative
possible change.

Nowadays the python-apt change in question is long in the past, so your
change looks correct to me, since it more accurately describes what
python-apt needs.

I might be inclined to suggest renaming _is_real_file, since its name is
a little misleading now.  Maybe _has_fileno?

-- 
Colin Watson                                       [cjwatson at debian.org]