pprint for dict in sorted order or insert order?

[josephsmeng]

BPO	30670
Nosy	@rhettinger, @serhiy-storchaka, @josephsmeng, @pombredanne, @aaronchall, @eamanu, @remilapeyre, @tirkarthi, @ewjoachim
PRs	bpo-30670: Add pp function to the pprint module #11769 bpo-30670: Add pp function to the pprint module #11769 bpo-30670: Add pp function to the pprint module #11769 bpo-30670: Fix typo in pprint docs #12500

^{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 2019-03-22.17:24:37.317>
created_at = <Date 2017-06-15.02:15:55.228>
labels = ['3.8', 'type-bug', 'library']
title = 'pprint for dict in sorted order or insert order?'
updated_at = <Date 2019-03-23.01:17:06.773>
user = 'https://github.com/josephsmeng'

bugs.python.org fields:

activity = <Date 2019-03-23.01:17:06.773>
actor = 'xavierguihot'
assignee = 'none'
closed = True
closed_date = <Date 2019-03-22.17:24:37.317>
closer = 'rhettinger'
components = ['Library (Lib)']
creation = <Date 2017-06-15.02:15:55.228>
creator = 'josephsmeng'
dependencies = []
files = []
hgrepos = []
issue_num = 30670
keywords = ['patch', 'patch', 'patch']
message_count = 19.0
messages = ['296056', '296065', '296068', '305440', '305442', '310898', '327904', '334588', '334605', '334689', '334693', '334846', '334854', '334932', '334933', '334936', '334937', '338614', '338615']
nosy_count = 11.0
nosy_names = ['rhettinger', 'serhiy.storchaka', 'josephsmeng', 'pombredanne', 'Aaron Hall', 'eamanu', 'remi.lapeyre', 'xtreak', 'Jan-Hein B\xc3\xbchrman', 'Valentin Beyer', 'ewjoachim']
pr_nums = ['11769', '11769', '11769', '12500']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue30670'
versions = ['Python 3.8']

[josephsmeng]

start from 3.6+, dict keys are ordered heir creation order.
the builtin print function works as we expected, but for
pprint, the keys is sorted. should we using the sorted version
or just obey the creation order as builtin print?

[rhettinger]

Until dict insertion order is guaranteed, it doesn't make sense to change pprint().

[serhiy-storchaka]

Concur with Raymond.

[aaronchall]

If/when order is guaranteed (3.7?) we should have a pprint that respects current order,

-or-

we should get an improved pprint (maybe named pp or print?) that understands mappings and other abstract data types.

I had a conversation about pprint at the Python meetup last night. It kinda went like this: https://www.youtube.com/watch?v=NpYEJx7PkWE

Maybe now's the time for improved behavior?

[serhiy-storchaka]

A year ago I proposed to add a method for detecting whether a dict preserves an order and in what sense. [1] But this idea was rejected.

[1] https://mail.python.org/pipermail/python-dev/2016-October/146597.html

[pombredanne]

IMHO since Guido said that dictionary order is guaranteed going forward [1], the order should now be preserved in 3.6+

Getting a sorted pprint'ed dict in a Py3.6.1 was a surprise to me coming from Python2.

The default ordered dict is to me the killer feature of 3 and a major driver to migrate from 2.

[1] https://mail.python.org/pipermail/python-dev/2017-December/151286.html

[Jan-HeinBhrman]

@terry.reedy - If I understand correctly, this issue was closed by you awaiting what would happen with the dict insertion order after 3.6.

It has been decided that dict insertion will stay for now and in the future. >>> Should this issue now be reopened?

And I would favor backward compatibility (key sort order) with an additional keyword for pprint to display it "unsorted" order (from pprint perspective, insertion order for dicts and OrderedDicts, and whatever other order for whatever other dicts).

[ValentinBeyer]

Please reopen this.
With version 3.7 and guaranteed dict order pprint should not sort by key.

[josephsmeng]

I reopened this issue, and change affected versions to 3.6, 3.7 and 3.8.