Fixes#4288.
- Default imports to THIRD_PARTY, so in effect we merge the FIRST_PARTY and THIRD_PARTY stubs. This means import order is no longer affected by whether typing_extensions is installed locally.
- Treat typing_extensions, _typeshed and some others as standard library modules.
Note that isort master is very different from the latest release; we'll have to do something
different if and when the next isort release comes out.
This is a follow-up on #4232. memoryview, hashlib, and hmac are updated
to use ReadableBuffer type instead of their own home-spun unions of
bytes, bytearray and whatever else each use case used. mmap is being
handled in #4244, and I'll leave BinaryIO for another day (or possibly
another person) because it's going to require some messy code
duplication because the relevant methods are defined in IO[AnyStr].
There's one corner case I'm not quite sure how best to handle: the
documentation for hmac.digest claim that the parmaeters have the same
meanings as in hmac.new, but in CPython the latter has an explicit check
that `key` is bytes or bytearray while the former works with a
memory-view. For now I've matched the documentation.
Also, the documentation for HMAC.update says that `msg` can be any type
supported by hashlib from Python 3.4; but I can't see anything in the
Python 2.7 implementation that would prevent it also taking bytes-like
objects, so I've not tried to treat Python 2 any different to Python 3.
This commit reorders any overloads where the first overload was
"shadowing" the second, preventing it from ever being matched by type
checkers that work by selecting the first matching overload alternative.
For example, the first overload alternative below is strictly broader
then the second, preventing it from ever being selected:
class Parent: pass
class Child(Parent): pass
@overload
def foo(x: *int) -> Parent: ...
@overload
def foo(x: int, y: int) -> Child: ...
The correct thing to do is to either delete the second overload or
rearrange them to look like this:
@overload
def foo(x: int, y: int) -> Child: ...
@overload
def foo(x: *int) -> Parent: ...
Rationale: I'm currently [working on a proposal][0] that would amend
PEP 484 to (a) mandate type checkers check overloads in order and
(b) prohibit overloads where an earlier alternative completely shadows
a later one.
[0]: https://github.com/python/typing/issues/253#issuecomment-389262904
This would prohibit overloads that look like the example below, where
the first alternative completely shadows the second.
I figured it would be a good idea to make these changes ahead of time:
if my proposal is accepted, it'd make the transition smoother. If not,
this is hopefully a relatively harmless change.
Note: I think some of these overloads could be simplified (e.g.
`reversed(...)`), but I mostly stuck with rearranging them in case I was
wrong. The only overload I actually changed was `hmac.compare_digest` --
I believe the Python 2 version actually accepts unicode.
