bytes does not implement __bytes__()

[FHTMitchell]

BPO	33055
Nosy	@terryjreedy, @serhiy-storchaka, @FHTMitchell
Superseder	bpo-24234: Should we define complex.complex and bytes.bytes?

^{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 2018-03-29.00:04:41.868>
created_at = <Date 2018-03-12.14:28:02.041>
labels = ['interpreter-core', '3.8', 'type-bug', '3.7']
title = 'bytes does not implement __bytes__()'
updated_at = <Date 2018-03-29.00:04:41.867>
user = 'https://github.com/FHTMitchell'

bugs.python.org fields:

activity = <Date 2018-03-29.00:04:41.867>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2018-03-29.00:04:41.868>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2018-03-12.14:28:02.041>
creator = 'FHTMitchell'
dependencies = []
files = []
hgrepos = []
issue_num = 33055
keywords = []
message_count = 4.0
messages = ['313653', '313666', '313977', '314624']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'serhiy.storchaka', 'FHTMitchell']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '24234'
type = 'behavior'
url = 'https://bugs.python.org/issue33055'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[FHTMitchell]

Every object which has a corresponding dunder protocol also implements said protocol with one exception:

>>> 'hello'.__str__()
'hello'

>>> (3.14).__float__()
3.14

>>> (101).__int__()
101

>>> True.__bool__()
True

>>> iter(range(10)).__iter__()
<range_iterator at 0xf6b08b0>

>> b'hello'.__bytes__()
---------------------------------------------------------------------------

AttributeError                            Traceback (most recent call last)
----> 1 b'hello'.__bytes__()

AttributeError: 'bytes' object has no attribute '__bytes__'

This was brought up on SO as being inconsistent: https://stackoverflow.com/questions/49236655/bytes-doesnt-have-bytes-method/49237034?noredirect=1#comment85477673_49237034

[serhiy-storchaka]

This isn't one exception. For example complex doesn't have the __complex__ method.

__str__, __float__, __int__ and __bool__ are implemented in str, float, int and bool because there are corresponding special slots in a type object. But __bytes__ and __complex__ were added later and they have no slots. Calling them for bytes and complex will slowdown creating new object.

The user code rarely needs to call these methods directly. Just call bytes(), complex(), str(), float(), etc.

[terryjreedy]

It is against Guido's general policy to add things not needed purely for consistency. Unless there is a compelling use case, I think this should be closed.

FHTM: I don't think Serhiy posts on SO, so you might consider adding his answer to yours, or make it a separate answer.

[serhiy-storchaka]

In any case this is a duplicate of 24234