sets and subsets

[Peter Otten]

Bart Nessux wrote:

> By using lists, I can create sets of number. Suppose I have three lists.
> One list is the super-set, one is a set that contains all the numbers
> (just like the super-set) and the last is sub-set of the super-set. For
> example:
> 
> a = [1,2,3,4,5]       # The super-set.
> b = [1,2,3,4,5] # Looks just like the super-set, but it's not.
> c = [2,4]     # A sub-set
> 
> I'd like to remove 2 & 4 from set b BECAUSE they are present in set c...
> this would make the sets look like this:
> 
> a = [1,2,3,4,5]
> b = [1,3,5]
> c = [2,4]
> 
> How do I test set c to find what it contains and then look at set b to
> see if it contains any of those same numbers, and if so, remove them.

You want set operations, so why would you use lists?

>>> from sets import Set
>>> a = Set([1,2,3,4,5])
>>> c = Set([2,4])
>>> b = a - c
>>> b
Set([1, 3, 5])

Peter