General computer language, syntax question.

MRAB python at mrabarnett.plus.com
Mon Feb 29 09:07:02 EST 2016


On 2016-02-29 13:45, jonas.thornvall at gmail.com wrote:
> I have a problem programming uniform networks, "x nodes with y links" that turn out to be really hairy to solve for me and i feel i really lack the programming features
>
> "Actually i program in javascript" but the problem seem general for all programming languages including Pyhton.
>
> For a beautiful solution it would require "If in list/array return boolean" "If not in list/array return boolean".
>
> But there is no such feature Python nor Javascript, so instead i set boolean value "inlist" to false and loop thru, to see if it is already in list. If not it is added to list.
>
> So if the current node i generate links for is x and i try to generate a link to  node z, and z's links exhausted i will add it to exhausted list.
>
> And if there is node-x exhausted entries in list, well then script should break because it will lock into a cycle. The cyclic lockup is due to only a subset of the networks on the form (links*deep)+1=nodes is possible.
>
> So what i need is to know howto write "if list/array ***empty*** do {something}"
>
> I sure know howto check if an array have 1 element 2,3,4 but how do you check for empty.
>
> I think it is crazy that you can not do general comparissons of the type
> If in list/array
> If not in list/array
>
> But it is even more crazy that you can not check if list/array is empty, that is just madness.
>
Does this help?

 >>> items = ['a', 'b', 'c', 'd', 'e']
 >>> 'c' in items
True
 >>> 'f' in items
False
 >>> len(items)
5
 >>> len([])
0



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