[Python-Dev] __all__ for pickle

[Jeremy Hylton]

I was just testing Zope with the latest CVS python and ran into
trouble with the pickle module.

The module has grown an __all__ attribute:

__all__ = ["PickleError", "PicklingError", "UnpicklingError", "Pickler",
           "Unpickler", "dump", "dumps", "load", "loads"]

This definition excludes a lot of other names defined at the module
level, like all of the constants for the pickle format, e.g. MARK,
STOP, POP, PERSID, etc.  It also excludes format_version and
compatible_formats. 

I don't understand why these names were excluded from __all__.  The
Zope code uses "from pickle import *" and writes a custom pickler
extension.  It needs to have access to these names to be compatible,
and I can't think of a good reason to forbid it.

What's the right solution?  Zap the __all__ attribute; the namespace
pollution that results is fairly small (marshal, sys, struct, the
contents of tupes).  Make __all__ a really long list?

I wonder how much breakage we should impose on people who use "from
... import *" for Python 2.1.  As you know, I was an early advocate of
the it's-sloppy-so-let-em-suffer philosophy, but I have learned the
error of my ways.  I worry that people will be unhappy with __all__ if
other modules suffer from similar code breakage.

Has __all__ been described by a PEP?  If so, it ought to be posted to
c.l.py for discussion.  If not, we should probably write a short PEP.
It would probably be a page of text, but it would help clarify that
confusion that persists about what __all__ is for and what its
consequences are.

Jeremy