[Tutor] Faster procedure to filter two lists . Please help

[Gonçalo Rodrigues]

Alan Gauld wrote:
> By missing out a loop(*) and some splits it should speed up 
> significantly for the cost of some small added complexity in building
>  the dictionaries in the first case.
> 
> (*)In fact 3 loops because you aren't doing len() which effectively 
> loops over the collection too.
> 

It this correct? Python lists are not linked-lists (as in Scheme, for
example). They are more like arrays (or vectors in C++/Java) with a
little more sofistication built into them to allow, for example, to
amortize over time a sequence of append operations. But in a nutshell,
len is actually a field in the underlying C object so len() is a
constant (O(1)) and as-fast-as-it-can-be operation.

Someone correct me, please, If I'm wrong.

Best regards,
G. Rodrigues