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

Guido van Rossum guido at python.org
Thu Dec 11 18:00:27 EST 2003

> Is there a reason the universal newline mode doesn't cover this case > already?

This module lets you explicitly create a text data file for any platform. The universal newline feature of python is for Python modules only, and lets you transparently import and exec Python source files with the different line ending formats. That is a different thing.

I suggest you go back and read the docs for open() in Python 2.3 again, you are confused with a different feature.

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).

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).

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.

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".

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

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