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To: python-list@python.org
From: Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject: Re: True == 1 weirdness
Date: Wed, 16 Sep 2015 09:28:54 -0400
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Xref: csiph.com comp.lang.python:96679

On Wed, 16 Sep 2015 05:16:21 -0700 (PDT), "Blake T. Garretson"
<blake.garretson@gmail.com> declaimed the following:

>I am maintaining some old code where the programmer used 1 for True because booleans hadn't been added to Python yet.  I'm getting some weird behaviour, so I created some simple tests to illustrate my issue.
>
>>>> 1 in {1:1}        #test1
>True
>>>> 1 in {1:1} == 1   #test2
>False
>>>> (1 in {1:1}) == 1 #test3
>True
>>>> 1 in ({1:1} == 1) #test4
>Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
>TypeError: argument of type 'bool' is not iterable
>>>>
>
>You can see that in the first test we get True as expected.  The second test yield False, because True does not equal 1, apparently.  Fair enough.  But then the third test yields True.  Weird.  Okay, so maybe it was evaluating the right side first?  So I put the parens over to the right and it fails, so that wasn't it.  So why do the second and third test differ?

	Most likely, you've run into chained conditionals...

	a < x < b

is interpreted as

	a < x AND x < b

so...

	1 in {1:1} == 1

becomes

	1 in {1:1} AND {1:1} == 1

	True AND False
	False

	I'll admit, I didn't think the "in" operation took part in chaining.
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/