M.-A. Lemburg wrote:
> Nick Coghlan wrote:
>
>> Guido van Rossum wrote:
>>
>>> What do people think? (My main motivation for this, as stated before,
>>> is that it adds complexity without much benefit.)
>>
>>
>>
>> I'm in favour, since it removes the "an unbound method is almost like
>> a bare function, only not quite as useful" distinction. It would allow
>> things like str.join(sep, seq) to work correctly for a Unicode separator.
>
>
> This won't work. Strings and Unicode are two different types,
> not subclasses of one another.
My comment was based on misremembering how str.join actually works. It
automatically flips to Unicode when it finds a Unicode string in the sequence -
however, it doesn't do that for the separator, since that should already have
been determined to be a string by the method lookup machinery.
However, looking at the code for string_join suggests another possible issue
with removing unbound methods. The function doesn't check the type of the first
argument - it just assumes it is a PyStringObject.
PyString_Join adds the typecheck that is normally performed by the method
wrapper when str.join is invoked from Python.
The issue is that, if the unbound method wrapper is removed,
str.join(some_unicode_str, seq) will lead to PyString_AS_STRING being invoked on
a PyUnicode object. Ditto for getting the arguments out of order, as in
str.join(seq, separator). At the moment, the unbound method wrapper takes care
of raising a TypeError in both of these cases. Without it, we get an unsafe
PyString macro being applied to an arbitrary type.
I wonder how many other C methods make the same assumption, and skip type
checking on the 'self' argument? It certainly seems to be the standard approach
in stringobject.c.
Regards,
Nick.
--
Nick Coghlan | ncoghlan at email.com | Brisbane, Australia
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