Issue with Python’s Floor Division

[yaoway]

BPO	42788
Nosy	@rhettinger, @ericvsmith

^{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 2020-12-30.17:43:51.912>
created_at = <Date 2020-12-30.17:31:26.585>
labels = ['interpreter-core', 'invalid', 'type-bug', '3.8']
title = 'Issue with Python\xe2\x80\x99s Floor Division'
updated_at = <Date 2020-12-30.17:46:52.533>
user = 'https://bugs.python.org/yaoway'

bugs.python.org fields:

activity = <Date 2020-12-30.17:46:52.533>
actor = 'eric.smith'
assignee = 'none'
closed = True
closed_date = <Date 2020-12-30.17:43:51.912>
closer = 'rhettinger'
components = ['Interpreter Core']
creation = <Date 2020-12-30.17:31:26.585>
creator = 'yao_way'
dependencies = []
files = []
hgrepos = []
issue_num = 42788
keywords = []
message_count = 4.0
messages = ['384073', '384076', '384078', '384079']
nosy_count = 3.0
nosy_names = ['rhettinger', 'eric.smith', 'yao_way']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42788'
versions = ['Python 3.8']

[yaoway]

There might be an issue with Python’s floor division:
Experienced Behavior: >>> (1 / 1) // 1 --> 1.0; >>> (0 / 1) // 1 --> 0.0
Expected Behavior: >>> (1 / 1) // 1 --> 1; >>> (0 / 1) // 1 --> 0

[rhettinger]

The current behavior was specified in PEP-238:

int / int -> float
float // int -> float

See: https://www.python.org/dev/peps/pep-0238/#semantics-of-floor-division

[ericvsmith]

Regular division (/) yields a float, so 1 / 1 is 1.0.

https://docs.python.org/3/reference/expressions.html#binary-arithmetic-operations says that for floor division, the arguments are first converted to a common type, which here would be float.

So, your examples are basically:

>>> 1 / 1
1.0
>>> 1.0 // 1
1.0

>>> 0 / 1
0.0
>>> 0.0 // 1
0.0

This is working as expected, and is not a bug.

[ericvsmith]

Oops, my message collided with rhettinger.