checking if two things do not equal None

Rustom Mody rustompmody at gmail.com
Sun Mar 30 04:54:09 CEST 2014


On Sunday, March 30, 2014 8:09:45 AM UTC+5:30, Roy Smith wrote:
> I have no particular problem with

>  x < 2 < y

> because it fits the same pattern.  But, if you show me

>  a != None != b:

> my brain just goes into overload.  Honestly, I don't even know what that 
> means.  My brain keeps trying to stick a, None, and b on Mrs. Albaum's 
> number line and keeps walking into the wall.  If you (the editorial you) 
> tell me that my failure to grok that expression means I'm not fluent in 
> Python, well then, guilty as charged.

<Math Terminology>
A relation that is reflexive antisymmetric and transitive is a partial order
Strict order: Irreflexive asymmetric and transitive
Both are strongly related
For general R (partial) S (strict)

S from R
xSy = xRy ∧ x ≠ y
R from S
xRy = xSy ∨ x=y
</Math Terminology>

For both these chained comparisons are natural

!= is not transitive: 2 != 3 and 3  != 2 ⊬ 2 == 2

So for != chained comparisons are not natural (or IMHO appropriate)



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