"in" operator doesn't return boolean

[DamjanKoir]

BPO	14247
Nosy	@birkenfeld

^{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 2012-03-10.18:11:06.673>
created_at = <Date 2012-03-10.18:01:02.115>
labels = ['invalid']
title = '"in" operator doesn\'t return boolean'
updated_at = <Date 2012-03-10.18:11:06.671>
user = 'https://bugs.python.org/DamjanKoir'

bugs.python.org fields:

activity = <Date 2012-03-10.18:11:06.671>
actor = 'georg.brandl'
assignee = 'none'
closed = True
closed_date = <Date 2012-03-10.18:11:06.673>
closer = 'georg.brandl'
components = ['None']
creation = <Date 2012-03-10.18:01:02.115>
creator = 'Damjan.Ko\xc5\xa1ir'
dependencies = []
files = []
hgrepos = []
issue_num = 14247
keywords = []
message_count = 2.0
messages = ['155329', '155332']
nosy_count = 2.0
nosy_names = ['georg.brandl', 'Damjan.Ko\xc5\xa1ir']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue14247'
versions = ['Python 2.7']

[DamjanKoir]

In operator acts like it doesn't return a boolean value

>>> 3 in [1,2,3] == True
False

and even

>>> 3 in [1,2,3] == 3 in [1,2,3]
False

but somehow if you add ( ) it starts working

>>> (3 in [1,2,3]) == True
True

Tested on OSX 10.7 Python 2.7.1

[birkenfeld]

Chaining comparison operators inserts implicit "and" conditions:

a OP b OP c OP d

is equivalent to

(a OP b) and (b OP c) and (c OP d)

This is most useful with ==, <, <= and so forth, but "in" and "is" also count as comparison ops and have the same precedence.