This is the sort of `goto` that requires the reader to stare hard at
the code to unpick what it's doing.
On doing so, the answer is... not very much!
* It jumps from the bottom of the loop to almost the top; the effect
is to bypass the loop condition `s < end` and also the
`if`-condition `*s != '\\'`, acting as if both are true.
* We've just decremented `s`, after incrementing it in the `switch`
condition. So it has the same value as when `s == end` failed.
Before that was another increment... and before that we had
`s < end`. So `s < end` true, then increment, then `s == end`
false... that means `s < end` is still true.
* Also this means `s` points to the same character as it did for the
`switch` condition. And there was a `case '\\'`, which we didn't
hit -- so `*s != '\\'` is also true.
* That means this has no effect on the behavior! The most it might do
is an optimization -- we get to skip those two checks, because (as
just proven above) we know they're true.
* But gosh, this is the *invalid escape sequence* path. This does not
seem like the kind of code path that calls for extreme optimization
tricks.
So, take the `goto` and the label out.
Perhaps the compiler will notice the exact same facts we showed above,
and generate identical code. Or perhaps it won't! That'll be OK.
But then, crucially, if some future edit to this loop causes the
reasoning above to *stop* holding true... the compiler will adjust
this jump accordingly. One of us fallible humans might not.
* Use the 'p' format unit instead of manually called PyObject_IsTrue().
* Pass boolean value instead 0/1 integers to functions that needs boolean.
* Convert some arguments to boolean only once.
- 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)
pymalloc_alloc() now returns directly the pointer, return NULL on
memory allocation error.
allocate_from_new_pool() already uses NULL as marker for "allocation
failed".
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
Base PR for other PRs that want to play with `type.__call__` such as #13930 and #14589.
The author is really @markshannon I just made the PR.
https://bugs.python.org/issue37207
Automerge-Triggered-By: @encukou
PyObject_Malloc() and PyObject_Free() inlines pymalloc_alloc and
pymalloc_free partially.
But when PGO is not used, compiler don't know where is the hot part
in pymalloc_alloc and pymalloc_free.
Keeping an account of allocated blocks slows down _PyObject_Malloc()
and _PyObject_Free() by a measureable amount. Have
_Py_GetAllocatedBlocks() iterate over the arenas to sum up the
allocated blocks for pymalloc.
In development mode and in debug build, encoding and errors arguments
are now checked on string encoding and decoding operations. Examples:
open(), str.encode() and bytes.decode().
By default, for best performances, the errors argument is only
checked at the first encoding/decoding error, and the encoding
argument is sometimes ignored for empty strings.
* The UTF-8 incremental decoders fails now fast if encounter
a sequence that can't be handled by the error handler.
* The UTF-16 incremental decoders with the surrogatepass error
handler decodes now a lone low surrogate with final=False.
