[Python-Dev] Idle, site.py, and the release candidates

Terry Reedy tjreedy at udel.edu
Sun Mar 31 09:52:26 CEST 2013

On 3/31/2013 2:39 AM, Nick Coghlan wrote:
> On Sun, Mar 31, 2013 at 12:34 PM, Terry Jan Reedy <tjreedy at udel.edu 
> <mailto:tjreedy at udel.edu>>
>     I do not know enough about other circumstances in which
>     stdin.fileno would do something other than return 0 to be sure of
>     what the proper fix would be.  (I increasingly dislike bare
>     excepts as they hide the thinking and knowledge of the original
>     programmer. What exception was expected that should be passed away?)
> The other problem is that making *two* function calls inside a broad 
> try/except is almost always a terrible idea.

That too. I could not decide which function an exception was expected from.

> It seems to me that the intended logic is more like this:
>     try:
>         # Close stdin if it wraps any fd other than 0
>         close_stdin = (sys.stdin.fileno() != 0)
>     except (AttributeError, OSError, io.UnsupportedOperation):
>         # Also close stdin if it doesn't expose a file descriptor
>         close_stdin = True
>     if close_stdin:
>         try:
>             sys.stdin.close()
>         except Exception:
>             pass
>     raise SystemExit(code)
There are 4 possible situations for sys.stdin:
1. No .fileno
2. .fileno raises
3. .fileno() != 0
4. lfileno() == 0
I believe the current code calls .close for 1 and raises SystemExit for 
2-4. Your code calls for 1-3 and raises for 4. I suspect that is 
correct.  For an rc patch, the safest temporary patch would be to start 
.__call__ with

if sys.stdin.__name__ == 'PseudoInputFile': sys.stdin.close()

I would have to check that the name is correct as seen in the user 
process (cannot at moment).

The deeper problem, I think, is that none of sys.version, 
sys.hexversion, sys._version, sys.platform tell a program that it is 
running under Idle. It usually does not matter but there are a few 
situations in which it does.

Terry Jan Reedy

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