[Python-Dev] Silencing IO errors on del/dealloc? (original) (raw)

Guido van Rossum guido at python.org
Sun Feb 22 20:08:15 CET 2009

On Sun, Feb 22, 2009 at 11:02 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:

The Python version of IO lib has taken the stance that all errors happening in the destructor of an IO object are silenced. Here is the relevant code in IOBase:

def del(self) -> None: """Destructor. Calls close().""" # The try/except block is in case this is called at program # exit time, when it's possible that globals have already been # deleted, and then the close() call might fail. Since # there's nothing we can do about such failures and they annoy # the end users, we suppress the traceback. try: self.close() except: pass However, this seems very unreliable and dangerous to me. Users will not be warned if their IO objects are not closed properly (which might be due to programming errors), and data possibly gets corrupted.

OTOH the is a much larger category of false positives, where a close() call raise an exception for some spurious reason (see the quoted comment) but no harm is done; in the past the tracebacks printed for del by default have caused nothing but confuse users (who think something is seriously wrong but have no way to debug it).

The svn history of those lines may have more pointers.

I would like to change this behaviour so that the "try/except" enclosure above is removed, letting del at least print those (unraisable) errors on the console. Of course I also advocate doing so in the C version of the IO lib.

I'd be very wary of this change. That code has enough comments to make me believe that I put it in for a very good reason...

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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