Re: Loading Resources From a Python Module/Package

On Sat Jan 31 2015 at 1:29:43 PM Barry Warsaw <[email protected]> wrote:

> On Jan 31, 2015, at 01:07 PM, Donald Stufft wrote:
>
> >The reasons for not wanting to use a context manager are sort of
> intertwined
> >with each other.
> >
> >The competitor to this function is something like:
> >
> >    import os.path
> >    import time
> >
> >    LOGO_PATH = os.path.join(os.path.dirname(__file__), "logo.gif")
> >
> >    def print_logo_path():
> >        print(LOGO_PATH)
> >
> >
> >    while True:
> >        print_logo_path()
> >        time.sleep(1)
>
> I'm just wondering if that's extracted from a real example or whether it's
> just a possible use case you'd want to support.  It's not a use case I've
> ever
> needed.
>
> I reviewed a bunch of resource_filename() uses and in almost all cases it's
>
> 1. Crafting a path-y thing for some other API that only takes paths.
> 2. Constructing a path for essentially shutil.copy()'ing the file somewhere
>    else (e.g. a test http server's file vending directory).
>
> There are one or two where it might be inconvenient to use a context
> manager,
> but the majority of cases would be fine.
>
> >It makes it more akward to use anytime you need to use the file in
> multiple
> >locations or multiple times and since each context manager instance (in
> the
> >worst case) is going to need to get bytes, create a temp file, and write
> bytes
> >for each use of the context manager.
>
> Perhaps it makes sense to either provide two APIs and/or implement a higher
> level API on top of a lower-level one?
>
> >The other thing is that for the "common" case, where the resource is
> available
> >on the file system already because we're just using a FileLoader, there
> is no
> >need for an atexit handler or a temporary file at all. The context manager
> >would only really exist for the uncommon case where we need to write the
> data
> >to a temporary file. Using the atexit handler allows us to provide the
> best
> >API for the common case, without too much problem for the uncommon case.
>
> A context manager could also conditionalize the delete just like your
> proposal
> conditionalizes adding to the atexit handler.
>
> >Yes it does mean that in certain cases the temporary files may be left
> behind,
> >particularly with kill -9 or segfaults or what have you. However that case
> >already exists, the only thing the context manager does is narrow the
> window
> >of case where a kill -9 or a segfault can leave temporary files behind.
>
> Sure, but it reduces the window for leakage, which will probably be enough.
>

I'm with Barry not wanting to rely on atexit when a context manager is
explicit and will clean up any state as necessary.

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