- drop TargetScopeError in favour of raising SyntaxError directly
  as per the updated PEP 572
- comprehension iteration variables are explicitly local, but
  named expression targets in comprehensions are nonlocal or
  global. Raise SyntaxError as specified in PEP 572
- named expression targets in the outermost iterable of a
  comprehension have an ambiguous target scope. Avoid resolving
  that question now by raising SyntaxError. PEP 572
  originally required this only for cases where the bound name
  conflicts with the iteration variable in the comprehension,
  but CPython can't easily restrict the exception to that case
  (as it doesn't know the target variable names when visiting
  the outermost iterator expression)

There are plenty of legitimate scripts in the tree that begin with a
`#!`, but also a few that seem to be marked executable by mistake.

Found them with this command -- it gets executable files known to Git,
filters to the ones that don't start with a `#!`, and then unmarks
them as executable:

    $ git ls-files --stage \
      | perl -lane 'print $F[3] if (!/^100644/)' \
      | while read f; do
          head -c2 "$f" | grep -qxF '#!' \
          || chmod a-x "$f"; \
        done

Looking at the list by hand confirms that we didn't sweep up any
files that should have the executable bit after all.  In particular

 * The `.psd` files are images from Photoshop.

 * The `.bat` files sure look like things that can be run.
   But we have lots of other `.bat` files, and they don't have
   this bit set, so it must not be needed for them.



Automerge-Triggered-By: @benjaminp

Implement PyBuffer_SizeFromFormat() function (previously
documented but not implemented): call struct.calcsize().

The fact that keyword names are strings is now part of the vectorcall and `METH_FASTCALL` protocols. The biggest concrete change is that `_PyStack_UnpackDict` now checks that and raises `TypeError` if not.

CC @markshannon @vstinner 


https://bugs.python.org/issue37540