[Python-Dev] Proposal for new core module: UserFIle (original) (raw)

Keith Dart kdart at kdart.com
Thu Dec 11 19:04:45 EST 2003

On Thu, 2003-12-11 at 15:00, Guido van Rossum wrote:

I also note that you change the meaning of readline() to return the line with the trailing separator stripped, and raise EOFError when you have reached the end. That's a big deviation from the standard file semantics, and shouldn't be done lightly in a subclass (it means that a TextFile instance is not substitutable for a regular file instance in most cases).

Yes, that is true, but I have had to use that semantic in other places (usually when using non-blocking sockets) and I personally prefer it. But as others have pointed out this functionality is not needed in Python 2.3 and so I will drop it.

Reviewing the rest of UserFile, I see several possibly useful additions (locking, fstat() etc.) and one semantic change that deserves to be a separate subclass or mix-in (the EINTR behavior).

And nothing that warrants the name "UserFile" (in fact, all the other UserXXX classes are specifically not subclasses of the native XXX class).

Yes, a lot of extra stuff was added later. Perhaps some should be factored out into a new module. Perhaps "filelib"? It was just more consistent for me, since I also have UserInt, UserFloat, and UserLong modules as well. But those are, thankfully, no longer needed either.

> No, mode r+ lets you create a single file descriptor that is in > read-write mode. The MergedIO lets you take who file objects (with > different file descriptors), one readable the other writable, and > combine them at the method-call level into one read-write object. This > is useful for pipes, or when you get file objects from libraries.

It looks like you are simply making all write operations go to the writable object and all the read operations go to the readable object. That's not a very sophisticated notion of "merging", and I'm not sure what the point is. Perhaps some examples of how you use this would help.

A quick example:

import os import UserFile

r, w = os.pipe() rf = os.fdopen(r) wf = os.fdopen(w)

fo = UserFile.MergedIO(rf, wf)

or

rwio = UserFile.MergedIO(sys.stdin, sys.stdout)

Perhaps "merged" is not the right word. It is not intended to merge files, but combine a separate read file object and write file object into one object that can be passed to other library methods that want a single read/write object (such as my "expect" module...)

I note that in general your proposals are low on motivation, which is going to do a lot of damage to your case if you don't fix this soon. You may be underestimating the level of motivation needed to get features added to the stdlib -- it's "batteries included" but also (to some extent) "TOOWTDI".

Hm, ok. more use cases? What I have submitted, and will submit, exist because I did need them for real work at some point, and have found them to be re-usable.

-- -- ------------------------------------------------------------------------- Keith Dart <mailto:kdart at kdart.com> <http://www.kdart.com/>

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