Removing None objects from a sequence

[J. Cliff Dyer]

On Mon, 2008-12-15 at 02:11 +0000, Lie Ryan wrote:
> On Fri, 12 Dec 2008 22:55:20 +0000, Steven D'Aprano wrote:
> 
> > On Fri, 12 Dec 2008 21:18:36 +0000, Lie Ryan wrote:
> >> Personally, I'd prefer VB's version:
> >> foo IsNot bar
> >> 
> >> or in pseudo-python
> >> foo isnot bar
> >> 
> >> since that would make it less ambiguous.
> > 
> > "a is not b" is no more ambiguous than "1+2*3". True, there's ambiguity
> > if you are ignorant of the precedence rules, but that's no worse than
> > saying that "+" is ambiguous if you don't know what "+" means.
> > 
> > "What's this 'is' operator??? It's ambiguous, it could mean ANYTHING!!!
> > Panic panic panic panic!!!"
> > 
> > *wink*
> > 
> > You're allowed to assume the normal conventions, and (lucky for me!)
> > despite being Dutch Guido choose to assume the normal English convention
> > that "a is not b" means the same as "not (a is b)" rather than "a is
> > (not b)". That's probably because the use-cases for the second would be
> > rather rare.
> > 
> > So given the normal precedence rules of Python, there is no ambiguity.
> > True, you have to learn the rules, but that's no hardship.
> 
> *I* know about the precedence rule, but a newbie or a tired programmer 
> might not. He might want to reverse the truth value of argument b but 
> instead has just reversed the whole expression. Probably in a slightly 
> convoluted code like this:
> 
> if a is not(b and c): 
>    ...
> 

A newbie might make that mistake, but a tired programmer would be
testing for equality rather than identity in that case, and if she
weren't, she'd have to fix her code in the morning anyway.

Cheers,
Cliff