[Python-Dev] transitioning from % to {} formatting (original) (raw)

Steven Bethard steven.bethard at gmail.com
Wed Sep 30 19:14:17 CEST 2009

On Wed, Sep 30, 2009 at 8:50 AM, Barry Warsaw <barry at python.org> wrote:

On Sep 30, 2009, at 11:39 AM, Steven Bethard wrote:

Thanks for the clarification. I generally like this approach, though it's not so convenient for argparse which already takes format strings like this::

parser = ArgumentParser(usage='%(prog)s [--foo]') parser.addargument( '--foo', type=int, default=42, help='A foo of type %(type)s, defaulting to %(42)s)

Yep, sorry, typo, that should have been %(default)s, not %(42)s.

I guess in this case I'm stuck with something like Benjamin's suggestion of adding an additional flag to control which type of formatting, and the corresponding 4 versions of cleanup. Ew. I missed Benjamin's suggestion, but in this case I would say add a flag to ArgumentParser.  I'm either going to want {} formatting all or nothing.  E.g. import argparse parser = ArgumentParser(usage='{prog} [--foo]', format=argparse.BRACES)

Yeah, that's basically Benjamin's suggestion, with the transition path being:

(1) Introduce format= keyword argument, defaulting to PERCENTS (2) Deprecate format=PERCENTS (3) Error on format=PERCENTS (Benjamin suggested just changing the default here, but that would give a release where errors would pass silently) (4) Deprecate format= keyword argument. (5) Remove format= keyword argument.

It's a little sad that it takes 5 versions to do this, but I guess if a user is on top of things, at version (1) they add format=BRACES to all their code, and then remove those at version (4). So even though there are 5 versions, there are only two code changes required.

At least in the case of argparse, this can be a constructor argument as you suggest, and we only have to introduce this flag in one place.

Steve

Where did you get that preposterous hypothesis? Did Steve tell you that? --- The Hiphopopotamus

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