`open()`able objects

[barneygale]

@rrolls

• Renaming duplex to random: I’m against this too, for multiple reasons:
  • Yes, we know that “random” means “random-access”, but the intuitive meaning is something akin to what you might use import random for. I don’t really think we should be using this term to mean “random-access” in new interfaces.
  • More importantly - “random” (or “random-access”) absolutely does not mean the same thing as “duplex”. “Duplex” means “you can both read from it and write to it”. “Random [access]” means “you can seek in it”. Seekability is a property of the file, so doesn’t need to be expressed in the method name (as I’ve mentioned in a previous post). Being duplex is a property of how you’re interacting with it, not the file itself.

Good point - thanks.

Just to throw out another option: the open() docs say that ‘+’ means opening for “updating”, so we could use _updater() perhaps

@rrolls

• Return types: We should still have three different return types to represent reader/writer/duplex (just like how in asyncio we have StreamReader and StreamWriter as separate types).

(I think it’s academic - we don’t generally add type annotations in the stdlib.)

We could use io.BufferedReader, io.BufferedWriter and io.BufferedRandom, but I suppose they’re too specific. In the typing module we have BinaryIO but it’s not further differentiated. Perhaps we could add typing.BinaryInput and typing.BinaryOutput?

@rrolls

• Q: What’s the difference in practice between using typing.BinaryIO and io.BufferedIOBase here? I see a switch from one to the other but no mention of why.

IIUC BufferedIOBase guarantees that all requested data is read/written in read() and write(), whereas this isn’t guaranteed in RawIOBase. But both of these classes are typing.BinaryIO nonetheless. Cody’s first reply explains it better.

@rrolls

• Q: Is there any reason buffering isn’t annotated as int?

I was trying to increase the signal-to-noise ratio for the purposes of this discussion, as we all seem to agree that it’s an int!