json fails to encode dictionary view types

[jogo]

BPO	39196
Nosy	@methane, @serhiy-storchaka

^{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 2020-01-04.02:32:27.302>
created_at = <Date 2020-01-02.19:10:57.980>
labels = ['3.7', '3.8', 'type-bug', 'library', '3.9']
title = 'json fails to encode dictionary view types'
updated_at = <Date 2020-01-04.02:32:27.301>
user = 'https://bugs.python.org/jogo'

bugs.python.org fields:

activity = <Date 2020-01-04.02:32:27.301>
actor = 'methane'
assignee = 'none'
closed = True
closed_date = <Date 2020-01-04.02:32:27.302>
closer = 'methane'
components = ['Library (Lib)']
creation = <Date 2020-01-02.19:10:57.980>
creator = 'jogo'
dependencies = []
files = []
hgrepos = []
issue_num = 39196
keywords = []
message_count = 3.0
messages = ['359212', '359216', '359272']
nosy_count = 3.0
nosy_names = ['methane', 'serhiy.storchaka', 'jogo']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue39196'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9']

[jogo]

Python 3 fails to encode dictionary view objects. Assuming this is an expected behavior, what is the thinking behind it? I was unable to find any documentation around this.

import json; json.dumps({}.values())
"TypeError: Object of type dict_values is not JSON serializable"

[serhiy-storchaka]

To handle non-standard types you can implement the default() method in the subclass of json.JSONEncoder (https://docs.python.org/3/library/json.html#json.JSONEncoder.default) or pass the corresponding argument to json.JSONEncoder() or json.dumps().

[methane]

If we support more types by default, user can not customize serialization of the type using default option.
That's why we don't accept "any iterable" but only list and tuple.