[Tutor] longest common substring

[Dave Angel]

On 11/13/2011 08:06 AM, lina wrote:
> <SNIP>
> Finally, if I am not wrong again, I feel I am kinda of starting
> figuring out what's going on. Why it's None.
>
> The main mistake here I use result = result.append(something)
> the "="
>
> I checked the print(id(result)) and print(id(result.append()),
>
> For the NoneType they shared the same id 8823392 in my laptop. is it
> temporary address?
>
None is a unique object, deliberately.  No matter how many times people 
create None, it'll always be the same object.  So
     a= None
     b = x.append(y)
     a is b           #(true)
     id(a) == id(b)        #(true)

Similarly  True and False are unique objects.

Other objects which are equal to each other may or may not have the same 
ID;  you should not count on it.  For example,
     x = 45+3
     y = 6*8

Checking  (x==y) is true, of course.  But checking (x is y) is 
indeterminate.  It may be true for the first ten tests you do, and false 
next time

-- 

DaveA