[Tutor] comparison function/built-in needed

[Kent Johnson]

joe_schmoe wrote:
> Greetings
> 
> I am attempting to compare the items in two lists across two criteria - 
> membership and position. For example:
> 
> list_a = [ 0, 4, 3, 6, 8 ]
> list_b = [ 1, 8, 4, 6, 2 ]
> 
> Membership = There are 3 items that are common to both lists, that is 3 
> items in list_a have membership in list_b (viz: 4, 6, 8);

Use sets:
  >>> list_a = [ 0, 4, 3, 6, 8 ]
  >>> list_b = [ 1, 8, 4, 6, 2 ]
  >>> set(list_a).intersection(list_b)
set([8, 4, 6])

> Position = There is 1 item in list_a that is also in the same position 
> in both lists (viz: 6).

Use zip() to iterate two lists in parallel and a list comprehension to accumulate the results:
  >>> [ a for a, b in zip(list_a, list_b) if a==b ]
[6]

or if you want the position of the item use enumerate() to get the index:
  >>> [ i for i, (a, b) in enumerate(zip(list_a, list_b)) if a==b ]
[3]

Kent