On Thu, Jan 16, 2014 at 12:31 AM, Serhiy Storchaka <storchaka at gmail.com> wrote: > getattr(foo, 'bar', None) is not the same as getattr(foo, 'bar'). So None > can't be used as universal default value. Not universal, but I still think that most functions don't need to have such a subtle distinction. E.g. in the case of sha1() I still believe that it's totally fine to switch the default to b''. In that particular case I don't see the need to also accept None as a way to specify the default. Basically, my philosophy about this is that anytime you can't easily reimplement the same signature in Python (without reverting to manually parsing the args using *args and **kwds) it is a pain, and you should think twice before canonizing such a signature. Also, there are two somewhat different cases: (a) The default can easily be expressed as a value of the same type that the argument normally has. This is the sha1() case. In this case I see no need to also accept None as an argument (unless it is currently accepted, which it isn't for sha1()). Another example is <stream>.read() -- here, passing in a negative integer means the same as not passing an argument. (b) The default has a special meaning that does something different than any valid value. A good example is getattr(), which must forever be special. To me, most functions should fall in (a) even if there is currently ambiguity, and it feels like repeat() was *meant* to be in (a). I'm not sure how AC should deal with (b), but I still hope that true examples are rare enough that we can keep hand-coding them. -- --Guido van Rossum (python.org/~guido)
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