RFC: file-like interface for Zope File and Image

[TinoW]

I'd like to implement an open() method for Zopes Image and File object
such that it is usable much like standard python file objects.

This should solve the following problems:

- efficient access in python scripts w/o the need of loading
  the whole data into a string using a non intuitive str(fileobject)
  (which even fails with Image objects, where you need to hack
  into the data structures)

- clean interface to classes deriving from these objects or
  using them (e.g Foto products etc)

I propose the following interface:

handle=fileobject.open(mode="r")

while it should default to "r" for text/* files
and "rb" for any other mime types.

handle.seek(offset,[whence])
handle.read([size])
 should we make size a sensible default here?

handle.write(), handle.truncate(), handle.writeline, ... etc.

readblock()
File-Objects use a pdata structure which is 128K block, readblock
would just read to the end of the current block and sets cursor
to the next block if any.

handle.next()

now thats interesting - python handles this with readline()
all the time. I'd like to use readline() for text/*
files and for all others rather use readblock() so its
easy to write:

for block in handle:
    dosomething(block)

in a most efficient way instead of:

while True:
    block=handle.readblock()
    if not block:
        break
    dosomething(block)

or even worser with read(128*1024)

I'd implement write() as truncating the file
from that point and write new blocks as
the data grows unless someone objects.

[TinoW (tino-wildenhain)]

discussion leads to the idea of having a blockiterator
like (readblock,) readblocks, xreadblocks
which return an ilterable. instead of changing the
behavior of next() for binary files.

[Andreas Jung (ajung)]

Changes: submitter email, edited transcript, importance (medium => low)

[Jens Vagelpohl (dataflake-deactivatedaccount-deactivatedaccount)]

Tino has never provided the promised implementation, marking this one as incomplete.

[Colin Watson (cjwatson)]

The zope2 project on Launchpad has been archived at the request of the Zope developers (see https://answers.launchpad.net/launchpad/+question/683589 and https://answers.launchpad.net/launchpad/+question/685285). If this bug is still relevant, please refile it at https://github.com/zopefoundation/zope2.