[Python-Dev] Deprecate codecs.open() and StreamWriter/StreamReader

[Antoine Pitrou]

On Tue, 24 May 2011 12:16:49 +0200
Walter Dörwald <walter at livinglogic.de> wrote:
> 
> > and so it's not possible to write a generic fix for
> > all child classes in the codecs module. Each stateful codec has to
> > handle special cases like seek() problems.
> 
> Yes, which in theory makes it possible to implement shortcuts for
> certain codecs (e.g. the UTF-32-BE/LE codecs could simply multiply the
> character position by 4 to get the byte position). However AFAICR none
> of the readers/writers does that.

And in practice, TextIOWrapper.tell() does a similar optimization in
a generic way. I'm linking to the Python implementation for readability:
http://hg.python.org/cpython/file/5c716437a83a/Lib/_pyio.py#l1741

TextIOWrapper.seek() is straightforward due to the structure of the
integer "cookie" returned by TextIOWrapper.tell().

In practice, TextIOWrapper gets much more love than
Stream{Reader,Writer} because it's an essential part of the new I/O
stack. As Victor said, problems which Stream* have had for years are
solved neatly in TextIOWrapper.

Therefore, leaving Stream{Reader,Writer} in is not a matter of "choice"
and "freedom given to users". It's giving people the misleading
possibility of using non-optimized, poorly debugged, less featureful
implementations of the same basic idea (an unicode stream abstraction).

Regards

Antoine.