dict.__contains__(unhashable) raises TypeError where False was expected

[xitop]

BPO	32675
Nosy	@methane

^{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 = <Date 2018-01-26.22:02:44.113>
created_at = <Date 2018-01-26.10:43:55.473>
labels = ['interpreter-core', 'invalid']
title = 'dict.__contains__(unhashable) raises TypeError where False was expected'
updated_at = <Date 2018-01-26.22:02:44.113>
user = 'https://bugs.python.org/xitop'

bugs.python.org fields:

activity = <Date 2018-01-26.22:02:44.113>
actor = 'r.david.murray'
assignee = 'none'
closed = True
closed_date = <Date 2018-01-26.22:02:44.113>
closer = 'r.david.murray'
components = ['Interpreter Core']
creation = <Date 2018-01-26.10:43:55.473>
creator = 'xitop'
dependencies = []
files = []
hgrepos = []
issue_num = 32675
keywords = []
message_count = 2.0
messages = ['310751', '310756']
nosy_count = 2.0
nosy_names = ['methane', 'xitop']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue32675'
versions = ['Python 3.6']

[xitop]

The dict.__contains() function does not fully comply with the description in the "Data Model" section of the official documentation, which states:
"contains(self, item) ... Should return true if item is in self, false otherwise."

Basically the same is written in "Mapping Types - dict": "key in d - Return True if d has a key key, else False."

According to that, testing a presence of an unhashable object in a dict should return False. But it raises a TypeError instead.

Example:
  >>> () in {}
  False
but:
  >>> [] in {}
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  TypeError: unhashable type: 'list'

There is a related SO question:
https://stackoverflow.com/questions/48444079/unexpected-behaviour-of-dictionary-membership-check
currently without a clear answer whether it is a bug or desired behaviour supposed to expose programming errors. In the latter case, it seems to be not documented.

[methane]

"Key must be hashable" is precondition of dict operations.

All operations for dict will raise TypeError for unhashable keys.
For example, d[k] will raise TypeError too, but document doesn't
mention about it:

"""
Return the item of d with key key. Raises a KeyError if key is not in the map.
"""
https://docs.python.org/3/library/stdtypes.html#dict