`fromfile` should raise an exception if not passed a “low-level file”

An ancient ticket from 2007 notes that fromfile does not work with files opened with gzip. Instead, it will interpret the literal gzip data. This is due to the fundamental way fromfile works and the resolution of the bug was essentially wontfix.

Secondly, it should be made clear in the documentation that you cannot pass a GzipFile. Some file-like objects trigger io.UnsupportedOperation.

It may save bugs and headaches if fromfile were to raise an Exception if it is passed a file-object that is not a low-level file.

[jzwinck]

Is there any reason not to implement this so it actually works? It’s been ten years since the bug was initially reported, and it’s still hurting people–for example https://stackoverflow.com/questions/47574607/python-gzip-module-doesnt-work-as-expected-on-ubyte-file/

It seems to me that it is possible to implement np.fromfile() so that it works with GzipFile (but not using readinto()).

[eric-wieser]

I think I agree with the consensus here that we should probably reopen this. Since closed issues are hard to rediscover, I’m going to reopen it for now - we can always close it again if another maintainer wants to argue strongly for it.

For every ancient issue we close with opposition, there are 10 which are unreproducible/irrelevant/already fixed - so it’s easy to be overzealous with closing,

Sometimes I wish we had fewer APIs for serialization / deserialization, especially for text formats…