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`.
When bpo-12015 got resolved by increasing the length of the
random string generated by _RandomNameSequence from six to eight
characters, the docstring of the class was not adjusted accordingly.
Issue #26604:
* Add a new optional source parameter to _warnings.warn() and warnings.warn()
* Modify asyncore, asyncio and _pyio modules to set the source parameter when
logging a ResourceWarning warning
The mkstemp() and mkdtemp() signatures have already been updated, but the
higher-level functions still suggest that the default values are forced to
text strings. Also merged some paragraphs describing the "suffix" and
"prefix" parameters, and pointed out that mktemp() does not support the new
changes.
