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[Alex Martelli]

Paul Watson <pwatson at redlinepy.com> wrote:

> "Alex Martelli" <aleaxit at yahoo.com> wrote in message 
> news:1h5760l.1e2eatkurdeo7N%aleaxit at yahoo.com...
> 
> > In today's implementations of Classic Python, yes.  In other equally
> > valid implementations of the language, such as Jython, IronPython, or,
> > for all we know, some future implementation of Classic, that may well
> > not be the case.  Many, quite reasonably, dislike relying on a specific
> > implementation's peculiarities, and prefer to write code that relies
> > only on what the _language_ specs guarantee.
> 
> How could I identify when Python code does not close files and depends on
> the runtime to take care of this?  I want to know that the code will work
> well under other Python implementations and future implementations which may
> not have this provided. 

Then you should use try/finally (to have your code run correctly in all
of today's implementations; Python 2.5 will have a 'with' statement to
offer nicer syntax sugar for that, but it will be a while before all the
implementations get around to adding it).

If you're trying to test your code to ensure it explicitly closes all
files, you could (from within your tests) rebind built-ins 'file' and
'open' to be a class wrapping the real thing, and adding a flag to
remember if the file is open; at __del__ time it would warn if the file
had not been explicitly closed.  E.g. (untested code):

import __builtin__
import warnings

_f = __builtin__.file
class testing_file(_f):
  def __init__(self, *a, **k):
     _f.__init__(self, *a, **k)
    self._opened = True
  def close(self):
    _f.close(self)
    self._opened = False
  def __del__(self):
    if self._opened:
       warnings.warn(...)
       self.close()

__builtin__.file = __builtin__.open = testing_file



Alex