cross-type comparison is different in python minor versions

[secalert]

BPO	23620
Nosy	@bitdancer
Files	python-float-decimal-comparison.txt

^{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 2015-03-09.13:14:03.682>
created_at = <Date 2015-03-09.10:35:47.270>
labels = ['interpreter-core', 'type-bug', 'invalid']
title = 'cross-type comparison is different in python minor versions'
updated_at = <Date 2015-03-09.13:14:03.680>
user = 'https://bugs.python.org/secalert'

bugs.python.org fields:

activity = <Date 2015-03-09.13:14:03.680>
actor = 'r.david.murray'
assignee = 'none'
closed = True
closed_date = <Date 2015-03-09.13:14:03.682>
closer = 'r.david.murray'
components = ['Interpreter Core']
creation = <Date 2015-03-09.10:35:47.270>
creator = 'secalert'
dependencies = []
files = ['38405']
hgrepos = []
issue_num = 23620
keywords = []
message_count = 2.0
messages = ['237632', '237644']
nosy_count = 2.0
nosy_names = ['r.david.murray', 'secalert']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue23620'
versions = ['Python 3.4']

[secalert]

Python internal compare function does not verify if a comparison of two objects is done by using object of the same type.

In this case python does not know how to compare DECIMAL and FLOATS and returns a FALSE instead of returning an Error.

Python should have strict rules to only allow comparison between objects is aware of but depending on the version of Python we have different behaviors:

# Output:
# Python 2.6.5 32bit -- WRONG: FLOAT seems comparable with DECIMAL (WRONG)
# Python 2.7.2 32bit -- WRONG: FLOAT seems comparable with DECIMAL (WRONG)
# Python 3.1.2 32bit -- CORRECT: FLOAT is NOT comparable with DECIMAL (CORRECT)
# Python 3.4.0 ([GCC 4.8.2] on linux) 32bit -- WRONG: FLOAT seems comparable with DECIMAL (WRONG)

A proof of concept code-snippet is attached.

[bitdancer]

In Python2, all objects were comparable (except DateTime stuff...and maybe there was one other exception, I forget). We did indeed decide this was a bug and fixed it in Python3. Now objects of different types are comparable if only if at least one of them supports being compared with the other. Python does, however, know how to compare Float and Decimal correctly, since Python 3.2 (see the What's New document for Python 3.2).