[Python-3000] Format specifier proposal

[Jim Jewett]

On 8/15/07, Ron Adam <rrr at ronadam.com> wrote:

> After each term is returned from the __format__ call, the results
> __format__ method is called with the next specifier.  GetTime.__format__
> returns a string.  str.__format__, aligns it.  A nice left to right
> sequence of events.

Is this a pattern that objects should normally follow, or a convention
enforced by format itself?  In other words, does

    "{0:abc,def,ghi}".format(value)

mean

    # Assume value.__format__ will delegate properly, to
    #    result1.__format__("def,ghi")
    #
    # There are some surprises when a trailing field size gets ignored by
    # value.__class__.
    #
    # Are  infinite loops more likely?
    value.__format__("abc,def,ghi")

or

    # The separator character (","?) gets hard to use in format strings...
    value.__format__("abc").__format__("def").__format__("ghi")

-jJ