Terry Reedy schrieb:
A Python interpreter has one encoding for floats, ints, and strings. sys.float_info and sys.int_info give details about the first two. although they are mostly invisible to user code. (I presume they are attached to sys rather than float and int precisely because this.) A couple of recent posts have discussed making the unicode encoding (UCS2 v 4) both less visible and more discoverable to extensions.
Bytes are nearly always an encoding of *something*, but the particular encoding used is instance-specific. As Guido has said, the programmer must keep track. But how? In an OO language, one obvious way is as an attribute of the instance. That would be carried with the instance and make it self-identifying.
What I do not know if it is feasible to give an immutable instance of a builtin class a mutable attribute slot.
As soon as you can mutate an instance, it is not an immutable type anymore. Calling it "immutable" despite will cause trouble. (The same bytes instance could be used somewhere else transparently, e.g. as a function default argument, or cached as a constant local.)
As for the usefulness, I often have to work with proprietary communication protocols between computer and devices, and there the bytes have no encoding whatsoever (though I agree that most bytes do have a meaningful encoding). However, a class as fundamental as "bytes" should not be burdened with an attribute that may not even apply -- it's easy to make a custom class to represent a (bytes, encoding) pair.