The _RandomSequence class in tempfile used to check the current pid every time its rng property was used.
This commit replaces this code with `os.register_at_fork` to reduce the overhead.
This implements things like `list[int]`,
which returns an object of type `types.GenericAlias`.
This object mostly acts as a proxy for `list`,
but has attributes `__origin__` and `__args__`
that allow recovering the parts (with values `list` and `(int,)`.
There is also an approximate notion of type variables;
e.g. `list[T]` has a `__parameters__` attribute equal to `(T,)`.
Type variables are objects of type `typing.TypeVar`.
Moreover, the following tests now check the child process exit code:
* test_os.PtyTests
* test_mailbox.test_lock_conflict()
* test_tempfile.test_process_awareness()
* test_uuid.testIssue8621()
* multiprocessing resource tracker tests
* bpo-30197: Enhance functions swap_attr() and swap_item() in test.support.
They now work when delete replaced attribute or item inside the with
statement. The old value of the attribute or item (or None if it doesn't
exist) now will be assigned to the target of the "as" clause, if there is
one.
* Update docstrings.
when a directory with the chosen name already exists on Windows as well as
on Unix. tempfile.mkstemp() now fails early if parent directory is not
valid (not exists or is a file) on Windows.
when a directory with the chosen name already exists on Windows as well as
on Unix. tempfile.mkstemp() now fails early if parent directory is not
valid (not exists or is a file) on Windows.
I have compared output between pre- and post-patch runs of these tests
to make sure there's nothing missing and nothing broken, on both
Windows and Linux. The only differences I found were actually tests
that were previously *not* run.
