gc.collect prints debug stats incorrectly

[chivay]

BPO	37990
Nosy	@ned-deily, @methane, @chivay
PRs	bpo-37990: fix gc stats #15626 [3.8] bpo-37990: fix gc stats (GH-15626) #15627

^{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 = 'https://github.com/methane'
closed_at = <Date 2019-08-31.01:53:18.110>
created_at = <Date 2019-08-30.21:22:40.527>
labels = ['interpreter-core', 'type-bug', '3.8', '3.9']
title = 'gc.collect prints debug stats incorrectly'
updated_at = <Date 2019-08-31.01:53:18.109>
user = 'https://github.com/chivay'

bugs.python.org fields:

activity = <Date 2019-08-31.01:53:18.109>
actor = 'methane'
assignee = 'methane'
closed = True
closed_date = <Date 2019-08-31.01:53:18.110>
closer = 'methane'
components = ['Interpreter Core']
creation = <Date 2019-08-30.21:22:40.527>
creator = 'chivay'
dependencies = []
files = []
hgrepos = []
issue_num = 37990
keywords = ['patch', '3.8regression']
message_count = 5.0
messages = ['350890', '350892', '350900', '350905', '350906']
nosy_count = 3.0
nosy_names = ['ned.deily', 'methane', 'chivay']
pr_nums = ['15626', '15627']
priority = 'high'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue37990'
versions = ['Python 3.8', 'Python 3.9']

[chivay]

Example:

Python 3.9.0a0 (heads/master:39d87b5471, Aug 30 2019, 23:19:13) 
[GCC 9.1.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import gc
>>> gc.set_debug(gc.DEBUG_STATS)
>>> gc.collect()
gc: collecting generation 2...
gc: objects in each generation: 589 4120 0
gc: objects in permanent generation: 0
gc: done, 0 unreachable, 0 uncollectable, %.4fs elapsed
0

[ned-deily]

Thanks for the report. It looks like this regression was introduced by the changes for bpo-37729.

[methane]

New changeset 013e52f by Inada Naoki in branch 'master':
bpo-37990: fix gc stats (GH-15626)
013e52f

[methane]

New changeset 97a31c7 by Inada Naoki in branch '3.8':
[3.8] bpo-37990: fix gc stats (GH-15626)
97a31c7

[methane]

Thank you for finding it!

My eyes were too focused on portability issue of "%zd"...