On Fri, Mar 27, 2020 at 3:29 PM Dennis Sweeney <sweeney.dennis...@gmail.com>
wrote:
> > > One may also continue using ``startswith()``
> > > and ``endswith()``
> > > methods for control flow instead of testing the lengths as above.
> > >
> > > That's worse, in a sense, since "foofoobar".removeprefix("foo") returns
> > "foobar" which still starts with "foo".
>
> I meant that startswith might be called before removeprefix, as it was
> in the ``deccheck.py`` example.
>
Not having read the full PEP, that wasn't clear to me. Sorry!
> > If I saw that in a code review I'd flag it for non-obviousness. One
> should
> > use 'string != new_string' unless there is severe pressure to squeeze
> > every nanosecond out of this particular code (and it better be inside an
> > inner loop).
>
> I thought that someone had suggested that such things go in the PEP,
I'm sure someone did. But not every bit of feedback is worth acting upon,
and sometimes a weird compromise is cooked up that addresses somebody's nit
while making things less understandable for everyone else. I think this is
one of those cases.
> but
> since these are more stylistic considerations, I would be more than happy
> to
> trim it down to just
>
> The builtin ``str`` class will gain two new methods which will behave
> as follows when ``type(self) is type(prefix) is str``::
>
> def removeprefix(self: str, prefix: str, /) -> str:
> if self.startswith(prefix):
> return self[len(prefix):]
> else:
> return self[:]
>
> def removesuffix(self: str, suffix: str, /) -> str:
> # suffix='' should not call self[:-0].
> if suffix and self.endswith(suffix):
> return self[:-len(suffix)]
> else:
> return self[:]
>
> These methods, even when called on ``str`` subclasses, should always
> return base ``str`` objects.
>
> Methods with the corresponding semantics will be added to the builtin
> ``bytes`` and ``bytearray`` objects. If ``b`` is either a ``bytes``
> or ``bytearray`` object, then ``b.removeprefix()`` and
> ``b.removesuffix()``
> will accept any bytes-like object as an argument. The two methods will
> also be added to ``collections.UserString``, with similar behavior.
>
Excellent!
--
--Guido van Rossum (python.org/~guido)
*Pronouns: he/him **(why is my pronoun here?)*
<http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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