[Import-SIG] Loading Resources From a Python Module/Package

[Barry Warsaw]

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.

Cheers,
-Barry
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