Don't return implicit optional types by get_type_hints

[ilevkivskyi]

BPO	33133
Nosy	@gvanrossum, @ilevkivskyi

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2018-03-24.18:16:02.475>
labels = ['3.7', '3.8', 'type-bug', 'library']
title = "Don't return implicit optional types by get_type_hints"
updated_at = <Date 2018-03-25.09:21:10.688>
user = 'https://github.com/ilevkivskyi'

bugs.python.org fields:

activity = <Date 2018-03-25.09:21:10.688>
actor = 'levkivskyi'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2018-03-24.18:16:02.475>
creator = 'levkivskyi'
dependencies = []
files = []
hgrepos = []
issue_num = 33133
keywords = []
message_count = 3.0
messages = ['314378', '314395', '314401']
nosy_count = 2.0
nosy_names = ['gvanrossum', 'levkivskyi']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue33133'
versions = ['Python 3.7', 'Python 3.8']

[ilevkivskyi]

Currently this code

def f(x: int = None):
 pass

get_type_hints(f)

returns{'x': Optional[int]}. I propose to abandon this behaviour. Although there is not yet a definitive decision about this aspect of PEP-484, see python/typing#275, I think at least at runtime we should not do this.

[gvanrossum]

I'm not sure we should change this ahead of a definitive decision. When you use mypy with the option that forbids it, your program will be invalid, and it doesn't really matter what we do at runtime; but that option is not the default yet, and without that option, mypy treats the type as Optional[int].

[ilevkivskyi]

OK, let us then keep this issue as a remainder that we need to update the runtime behaviour when the static one changes.

[AlexWaygood]

This behaviour was fixed in #30304:

C:\Users\alexw\coding\cpython>python
Running Debug|x64 interpreter...
Python 3.11.0a7+ (main, Apr 14 2022, 10:41:31) [MSC v.1931 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> def f(x: int = None):
... pass
...
>>> from typing import get_type_hints
>>> get_type_hints(f)
{'x': <class 'int'>}