Integer division numerical error

[jfu334]

BPO	43116
Nosy	@mdickinson

^{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 2021-02-03.14:03:28.166>
created_at = <Date 2021-02-03.13:49:36.044>
labels = ['3.8', 'type-bug', '3.7', '3.9', 'invalid']
title = 'Integer division numerical error'
updated_at = <Date 2021-02-03.14:03:28.165>
user = 'https://bugs.python.org/jfu334'

bugs.python.org fields:

activity = <Date 2021-02-03.14:03:28.165>
actor = 'mark.dickinson'
assignee = 'none'
closed = True
closed_date = <Date 2021-02-03.14:03:28.166>
closer = 'mark.dickinson'
components = []
creation = <Date 2021-02-03.13:49:36.044>
creator = 'jfu33.4'
dependencies = []
files = []
hgrepos = []
issue_num = 43116
keywords = []
message_count = 2.0
messages = ['386204', '386208']
nosy_count = 2.0
nosy_names = ['mark.dickinson', 'jfu33.4']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43116'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[jfu334]

I'm a bit confused because this seems to be too obvious to be a bug:

[code]
>>> -2094820900 // 1298
-1613884
>>> -2094820900 // -1298
1613883
[/code]

Obviously there is a +/- 1 difference in the result.

Tested with Python 3.7, 3.8 and 3.9 on Debian Bullseye. Am I missing something?

[mdickinson]

Python's // operator does floor division: that is, the (true) quotient is converted to an integer by taking the floor (rounding towards -infinity) instead of truncating (rounding towards zero).

So indeed it's not a bug. The behaviour is documented here: https://docs.python.org/3/reference/expressions.html#binary-arithmetic-operations

See also bpo-43034