[Python-Dev] TextIO seek and tell cookies

[Random832]

On Mon, Sep 26, 2016, at 05:30, Ben Leslie wrote:
> I think the case of JSON or SQL database is even more important though.
> 
> tell/seek can return 129-bit integers (maybe even more? my maths might
> be off here).
> 
> The very large integers that can be returned by tell() will break
> serialization to JSON, and storing in a SQL database (at least for
> most database types).
> 
> What is the value of comparing these to plain integers? Unless you
> happen to know the magic encoding it isn't going to be very useful I
> think?

I assume the value is that in the circumstances in which all of the
flags and other bits are zero, they can be used as offsets in precisely
the way that you used them. It may also be possible that in some cases
where they are not zero, doing arithmetic with them is still "safe"
since the real offset is still in the low-order bits. I don't know if
those circumstances are predictable enough for it to be worthwhile.
Changing it would obviously break code that does this (unless, perhaps,
it were changed to be a class with arithmetic operators), the question
is whether such code "deserves" to be broken.

In my own tests, even a UTF-8-sig file with DOS line endings "worked".
Does anyone have information about what circumstances can reliably cause
tell() to return values that are *not* simple integers? Maybe it has
something to do with working with stateful encodings like iso-2022 or
UTF-7?

What was the situation that caused your problem?