json.loads encoding parameter deprecation removal in Python 3.9

[tirkarthi]

BPO	39377
Nosy	@vstinner, @methane, @serhiy-storchaka, @ammaraskar, @tirkarthi
PRs	bpo-39377: json: Remove encoding option. #18075 bpo-39377: json: Update doc about the encoding option. #18076

^{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 2020-01-22.10:22:24.145>
created_at = <Date 2020-01-18.05:27:39.947>
labels = ['type-bug', 'library', '3.9']
title = 'json.loads encoding parameter deprecation removal in Python 3.9'
updated_at = <Date 2020-01-22.10:22:24.144>
user = 'https://github.com/tirkarthi'

bugs.python.org fields:

activity = <Date 2020-01-22.10:22:24.144>
actor = 'methane'
assignee = 'none'
closed = True
closed_date = <Date 2020-01-22.10:22:24.145>
closer = 'methane'
components = ['Library (Lib)']
creation = <Date 2020-01-18.05:27:39.947>
creator = 'xtreak'
dependencies = []
files = []
hgrepos = []
issue_num = 39377
keywords = ['patch']
message_count = 9.0
messages = ['360235', '360289', '360291', '360292', '360293', '360294', '360295', '360296', '360457']
nosy_count = 5.0
nosy_names = ['vstinner', 'methane', 'serhiy.storchaka', 'ammar2', 'xtreak']
pr_nums = ['18075', '18076']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue39377'
versions = ['Python 3.9']

[tirkarthi]

This is a followup of bpo-33461. The warning says about removal of the encoding parameter in 3.9 . It's already ignored since 3.1 hence I assume this should be raising a TypeError in 3.9 removing the deprecation warning. I am finding some projects using the encoding parameter though it has no effect. Since Python 3.9 has alpha 3 to be released it will be good to fix the deprecation in the early stage of release cycle.

[methane]

New changeset 5492bfc by Inada Naoki in branch 'master':
bpo-39377: json: Remove the encoding option. (GH-18075)
5492bfc

[tirkarthi]

Should we be raising an error if encoding is present on 3.9 as part of kwargs? It's obtrusive but for people going from Python 3.7 to 3.9 there will be no change and they will keep assuming encoding parameter is valid.

[ammaraskar]

Do you mean to say we should or shouldn't be raising an error? With Inada-san's change you get this:

>>> json.loads("true", encoding='utf8')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\ammar\workspace\cpython\lib\json\__init__.py", line 359, in loads
    return cls(**kw).decode(s)
TypeError: __init__() got an unexpected keyword argument 'encoding'

[methane]

If this broke some real-world software and the pain is high enough, we can revert the change and add one more deprecation period, like all other removals.

[tirkarthi]

Do you mean to say we should or shouldn't be raising an error? With Inada-san's change you get this:

Sorry, I misread the patch as only removal and didn't test the change completely.

I am filing issues on code that I can find using this pattern and will wait for the feedback during alpha cycle.

• Encoding parameter to json.loads is deprecated and will be removed in Python 3.9 ansible/ansible#66592
• Encoding parameter to json.loads is deprecated and will be removed in Python 3.9 jupyter/notebook#5165
• Encoding passed to json.loads was deprecated to be removed in Python 3.9 django-extensions/django-extensions#1465

[vstinner]

I reopen the issue.

New changeset 5492bfc by Inada Naoki in branch 'master':
bpo-39377: json: Remove the encoding option. (GH-18075)
5492bfc

Would you mind to document the removal in the following doc section?
https://docs.python.org/dev/whatsnew/3.9.html#removed

[serhiy-storchaka]

Please update the documentation which still mentions the encoding parameter.

[methane]

New changeset 5bbac8c by Inada Naoki in branch 'master':
bpo-39377: json: Update doc about the encoding option. (GH-18076)
5bbac8c