Exception handling on boolean comparisons

[CanisUrsa]

BPO	42394
Nosy	@stevendaprano, @CanisUrsa

^{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 2020-11-17.21:53:25.665>
created_at = <Date 2020-11-17.21:37:45.506>
labels = ['invalid', 'type-bug', '3.8']
title = 'Exception handling on boolean comparisons'
updated_at = <Date 2020-11-17.21:53:25.662>
user = 'https://github.com/CanisUrsa'

bugs.python.org fields:

activity = <Date 2020-11-17.21:53:25.662>
actor = 'steven.daprano'
assignee = 'none'
closed = True
closed_date = <Date 2020-11-17.21:53:25.665>
closer = 'steven.daprano'
components = []
creation = <Date 2020-11-17.21:37:45.506>
creator = 'CanisUrsa'
dependencies = []
files = []
hgrepos = []
issue_num = 42394
keywords = []
message_count = 2.0
messages = ['381289', '381291']
nosy_count = 2.0
nosy_names = ['steven.daprano', 'CanisUrsa']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42394'
versions = ['Python 3.8']

[CanisUrsa]

Python 3.8.6 will not produce an exception when comparing values in an and/or statement that normally produces an exception standalone.

val = 0
low = 1
high = "2"

The following makes sense:

val >= low : False
val <= high : Exception, cant compare int and str
val <= high and val >= low : Exception, cant compare int and str

The following doesn't make sense (doesn't produce an exception):

val >= low and val <= high : False

[stevendaprano]

This is not a bug, it is normal handling of and and or operators since Python 1.5 and possibly older.

The and and or operators are short-cut operators. This is intentional design, so we can write things like:

    if mylist and mylist[0] == value:

the mylist[0] == value expression is only evaluated if mylist is a truthy value.

This is all documented here:

https://docs.python.org/3/reference/expressions.html#boolean-operations