This argument is forwarded on to `Popen.__init__`, like most of the other arguments. It can be `None`, just like the `executable` parameter for all the other `subprocess` functions:
```pycon
>>> import subprocess
>>> subprocess.check_call(["python", "-c", "1/1"], executable=None)
0
>>> subprocess.check_call(["python", "-c", "1/0"], executable=None)
Traceback (most recent call last):
File "<string>", line 1, in <module>
ZeroDivisionError: division by zero
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\Users\alexw\AppData\Local\Programs\Python\Python310\lib\subprocess.py", line 369, in check_call
raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['python', '-c', '1/0']' returned non-zero exit status 1.
```
It's system-dependent. stubdefaulter told me `multiprocessing.heap.Heap: parameter size: stub default 4096 != runtime default 16384`, which presumably means it's 4096 on @AlexWaygood's system and 16384 on mine. I looked in the code and the default is set to `mmap.PAGESIZE`, which in turn is set from some system call at import time.
Continuing work towards #8988.
The first five commits were created using stubdefaulter on various Python versions; the following commits were all created manually by me to fix various problems. The main things this adds that weren't present in #9501 are:
- Defaults in Windows-only modules and Windows-only branches (because I'm running a Windows machine)
- Defaults in non-py311 branches
- Defaults for float parameters
- Defaults for overloads
The type has a custom __eq__:
https://github.com/python/cpython/blob/v3.11.1/Objects/descrobject.c#L1906
This helps fix this mypy false positive when using `--strict-equality`:
```
from types import MappingProxyType
p = MappingProxyType({'x': 1})
d = {'x': 1}
print(p == d) # error: Non-overlapping equality check
```
The fragment prints `True` so the comparison is valid.
Since python 3.7, asyncio.loop.create_datagram_endpoint expects the
arguments `local_addr` and `remote_addr` to be `str` or `None` when the
argument family=`socket.AF_UNIX` and the argument `sock` is `None` or
also a unix socket.
