On Sep 11, 2012, at 01:17 PM, Terry Reedy wrote: >This second example strikes me (naively, as English speaker but not argparse >user) as 'wrong' in that 'default' is being misused to mean 'start value that >is always used to generate the final value' [as in sum(iterable, start=0)], >rather than 'final value that is only used if nothing else is given' (as in >nearly all uses of 'default' in Python). Perhaps this is what you meant by >"semantic ambiguity".
Well, in a sense yes, that is an ambiguity so I won't quibble about whether it's the same one or not. :) >As I see it, storing is done *with* a default or explicit value, appending is >done *to* a start value *with* whatever. Perhaps reusing 'default' instead of >using a new name such as 'start' was a bit too clever for our own good ;-). I suspect that it's too late to change this, by say adding a 'start' parameter or some such, at least until Python 3.4. >> The fix for issue 12776 broke the last two lines of the second example, >> because in the no-command-line-arguments-given case, arg.test is the >> *string* "[]" and not the actual empty list object. > >This seems even more wrong (as in slightly crazy) as it switches the meaning >of 'default' within one parser example rather than between parser examples. And yet, that's how it works in 2.7, 3.2, and 3.3.1. >> It seems to me that the semantics could reasonably be implied to mean that >> the type converter should only be applied to the default value when >> action='store', as is the default. Then in the second example, because >> action='append', the type conversion would not be applied (it makes no >> sense to do so). > >I arrive at the same conclusion, I believe, by saying that for a given >parser, the type converter should always or never be applied to 'default', >which should mean converting or not when the parser is created. Append to >'default as base or start' should mean not converting. Does that mean that for fixing the regression, you favor applying the type conversion only for action='store' or by only applying it when the default is a string? It seems better to only apply the type conversion for action='store' but more backward compatible for the original behavior to only apply it when default is a string. Cheers, -Barry _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
