Guido van Rossum wrote:
> [Just addressing one little issue here; generally I'm just happy that
> we're discussing this issue in such detail from so many points of
> view.]
>
> On Mon, Jun 21, 2010 at 10:50 PM, Toshio Kuratomi <[email protected]> wrote:
>> [...] Would urljoin(b_base, b_subdir) => bytes and
>> urljoin(u_base, u_subdir) => unicode be acceptable though? (I think, given
>> other options, I'd rather see two separate functions, though. It seems more
>> discoverable and less prone to taking bad input some of the time to have two
>> functions that clearly only take one type of data apiece.)
>
> Hm. I'd rather see a single function (it would be "polymorphic" in my
> earlier terminology). After all a large number of string method calls
> (and some other utility function calls) already look the same
> regardless of whether they are handling bytes or text (as long as it's
> uniform). If the building blocks are all polymorphic it's easier to
> create additional polymorphic functions.
>
> FWIW, there are two problems with polymorphic functions, though they
> can be overcome:
>
> (1) Literals.
>
> If you write something like x.split('&') you are implicitly assuming x
> is text. I don't see a very clean way to overcome this; you'll have to
> implement some kind of type check e.g.
>
> x.split('&') if isinstance(x, str) else x.split(b'&')
>
> A handy helper function can be written:
>
> def literal_as(constant, variable):
> if isinstance(variable, str):
> return constant
> else:
> return constant.encode('utf-8')
>
> So now you can write x.split(literal_as('&', x)).
This polymorphism is what we used in Python2 a lot to write
code that works for both Unicode and 8-bit strings.
Unfortunately, this no longer works as easily in Python3 due
to the literals sometimes having the wrong type and using
such a helper function slows things down a lot.
It would be great if we could have something like the above as
builtin method:
x.split('&'.as(x))
Perhaps something to discuss on the language summit at EuroPython.
Too bad we can't add such porting enhancements to Python2 anymore.
--
Marc-Andre Lemburg
eGenix.com
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