[Python-ideas] a bad feature in Python syntax

[David Mertz]

OK, I'm impressed!

I've written about and taught Python for almost 20 years.  I never realized
`in` was a chained comparison.  I'm pretty sure I've never seen it used
that way "in the wild."  I also never tried using `is` in a chained way
until just now.

That said, there are at least three things perverse about the examples
below, and they should *definitely* never be used in real code.

This is vaguely plausible (for variable defined in some more interesting
way where the substring relation is not so obvious; say content read from
files):

>>> a = "a"
>>> b = "abc"
>>> c = "abcde"
>>> a in b in c
True


On Tue, Feb 28, 2017 at 6:56 PM, 语言破碎处 <mlet_it_bew at 126.com> wrote:

> I'm bited once:
>     >>> '' in {} == False
>     False
>     >>> ('' in {}) == False
>     True
>
>     # '' in {} == False ==>> ('' in {}) and ({} == False) ==>> False!
>
> I think only compare operations should be chained.
>
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>
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