feof status (was: Re: [Python-Dev] Rehabilitating fgets)
Guido van Rossum
Sun, 07 Jan 2001 11:52:11 -0500
> This mess reminds me. For some work I'm doing right now, it would be
> very useful if there were a way to query the end-of-file status of a
> file descriptor without actually doing a read.
I hope you really mean file object (== wrapper around stdio FILE
object). A file descriptor (small little integer in Unix) doesn't
have a way to find this out.
Even for file objects, it is typically only known that there's an EOF
condition after a lowest-level read operation returned 0 bytes. So in
effect you must still do a read in order to determine EOF status.
I just ran a small test program, and fread() appears to set the eof
status when it returns a short count. Normally, Python's read() uses
fread() so this might be useful. However after a readline(), you
can't know the eof status (unless the last line of the file doesn't
end in a newline).
> I don't see this ability anywhere in the 2.0 API. Questions:
> 1. Am I missing something obvious?
> 2. If the answer to 1 is that I am not, in fact, being a dumbass, what
> is the right way to support this? The obvious alternatives are an
> eof member (analogous to the existing `closed' member, or an eof()
> method. I favor the latter.
> 3. If we agree on a design, I'm willing to implement this at least for
> Unix. Should be a small project.
Before adding an eof() method, can you explain what your program is
trying to do? Is it reading from a pipe or socket? Then select() or
poll() might be useful.
--Guido van Rossum (home page: http://www.python.org/~guido/)