at what complexity, a comparison fails ?

[Steven D'Aprano]

On Mon, 31 Dec 2007 11:45:55 +0100, Stef Mientki wrote:

> hello,
> 
> I had a program that worked perfectly well. In this program modules were
> dynamically added, just by putting the file in a predefined directory.
> 
> Now one of the interface mechanisms was to see if some parameter was
> changed in a an instance,
> by comparing the value from the instance with its previous value
> 
> This went all well, untill I added a too complex variable, then the
> program stopped working, without generating exceptions.

What do you mean "stopped working"?


> So it seems that comparing a too complex value isn't allowed. the
> variable was something like:
> 
>   A = [ <ndarray>, <ndarray>, ..., [<color>,<color>,...], [<float>,
> <float>, ... ] ]

Doesn't seem complex to me, and I daresay probably not to Python either 
-- although a lot depends on what "ndarray" and "colour" are.


> So what I need was something like:
>     if  A != A_prev :
>         ... do something
>         A_prev = A
> 
> And this crashes, or at least it doesn't work but also doesn't generate
> exceptions.

It "crashes"? Explain please.



> It does seems to work, if A only contains 1 array.
> 
> Why am I not allowed to compare A and A_prev ?? And in general, how
> complex might a list be to make a valid comparison, or what are the
> rules ?

As complicated as you like.



-- 
Steven