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From: roy@panix.com (Roy Smith)
Newsgroups: comp.lang.python
Subject: Re: object.enable() anti-pattern
Date: 9 May 2013 14:59:26 -0400
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Xref: csiph.com comp.lang.python:45054

In article <518be931$0$29997$c3e8da3$5496439d@news.astraweb.com>,
Steven D'Aprano  <steve+comp.lang.python@pearwood.info> wrote:
> There is no sensible use-case for creating a file OBJECT unless it 
> initially wraps an open file pointer.

OK, I guess that's a fair statement.  But mostly because a python file
object only exposes those subset of operations you can do on file
descriptors which deal with reading and writing the contents of a
file.

It would not be true if python file objects included methods for
querying and manipulating file metadata.  It's not hard to imagine a
file class which could be used like:

f = file("/path/to/my/file")
f.delete()

That would be a totally different model from the current python file
object.  And then there would be plenty of things you might want to do
to a file other than open it...

file("/path/to/my/directory").chdir()
file("/dev/sdf").mount("/var/lib/whatever")
file("/mnt/swapfile").swapon()

> The standard C I/O library doesn't support creating a file
> descriptor unless it is a file descriptor to an open file [...]
> there is no corresponding function to create a *closed* file
> description. (Because such a thing would be pointless.)

What about sockets?  From the python standard library:

s = socket.socket()

Now what?  You can't do much with your shiny new socket until you call
bind() or connect(), or a few other things.  At least not for TCP.
This is essentially the two-phased construction pattern.  Of course,
the python socket module just exposes the semantics of the underlying
OS sockets, so there's not a lot of choice there.