open == file considered harmful (Re: [Python-Dev] RE: unuseable)

Guido van Rossum guido at
Tue Dec 16 18:38:20 EST 2003

> Michael Chermside <mcherm at>:
> > Suppose that had some code which had an object representing a
> > directory, with a method "open(filename, mode='r')" that opened 
> > files in the directory. Given this object, you could imagine 
> > constructing new objects with more limited capabilities.

Greg Ewing:

> With regard to files, we'd almost have something like that
> now, if it weren't for the unfortunate fact that the file
> type's constructor can be used to open any file.

Good observation.

> In light of this, it may have been a serious mistake to
> unify the 'file' type and the 'open' function. Is it too
> late to back out of that decision?

I think so.  But to remedy this, the file constructor could simply
refuse to open any files when called from restricted mode.  (Although
this would open up the same kind of holes that Samuele so cleverly
showed exist in other built-ins that do this kind of checking.)

(Re the capabilities discussion, this is Python 3.0 material if I ever
saw some; no time to respond in more detail, given that we've had this
thread before.)

--Guido van Rossum (home page:

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