Can't use sort_keys in json.dumps with mismatched types

[yoann934]

BPO	38046
Nosy	@nicktimko, @MojoVampire
PRs	bpo-25457: Remove sorting bug in json._iterencode_dict #15691
Superseder	bpo-25457: json dump fails for mixed-type keys when sort_keys is specified
Files	json_bug_exemple.py

^{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 2019-09-06.20:13:55.539>
created_at = <Date 2019-09-06.18:56:05.445>
labels = ['type-bug', 'library', '3.9']
title = "Can't use sort_keys in json.dumps with mismatched types"
updated_at = <Date 2019-09-07.09:56:29.366>
user = 'https://bugs.python.org/yoann934'

bugs.python.org fields:

activity = <Date 2019-09-07.09:56:29.366>
actor = 'python-dev'
assignee = 'none'
closed = True
closed_date = <Date 2019-09-06.20:13:55.539>
closer = 'josh.r'
components = ['Library (Lib)']
creation = <Date 2019-09-06.18:56:05.445>
creator = 'yoann934'
dependencies = []
files = ['48596']
hgrepos = []
issue_num = 38046
keywords = []
message_count = 3.0
messages = ['351268', '351269', '351270']
nosy_count = 3.0
nosy_names = ['nicktimko', 'josh.r', 'yoann934']
pr_nums = ['15691']
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '25457'
type = 'behavior'
url = 'https://bugs.python.org/issue38046'
versions = ['Python 3.9']

[yoann934]

If the dict included both str and int keys, sorted returns this error :
TypeError: '<' not supported between instances of 'int' and 'str'

It is a little bit problematic when used with default library behavior, as jsonify in Flask.

possible solution :
try:
items = sorted(dct.items())
except(TypeError):
items = sorted(dct.items(), key=lambda kv: str(kv[0]))

[nicktimko]

It's not clear what you suggest, but it is likely better to alert the user that their keys have mismatched types than to suppress it by default.

Perhaps alongside the sort_keys argument, you would like a parameter that gets passed into sorted() when the items are sorted?

Perhaps an additional argument, or if sort_keys is a callable, use that as the key argument to sorted?

strange = {"1":"one", 2:"ii"}
json.dumps(strange, sort_keys=True, key=str)
json.dumps(strange, sort_keys=str)
# {"1": "one", 2: "ii"}

[MojoVampire]

This is an exact duplicate of bpo-25457.