Python -Intersection of multiple lists?

Question

I am playing with python and am able to get the intersection of two lists:

result = set(a).intersection(b) 

Now if d is a list containing a and b and a third element c, is there an built-in function for finding the intersection of all the three lists inside d? So for instance,

d = [[1,2,3,4], [2,3,4], [3,4,5,6,7]] 

then the result should be

[3,4] 

Answer 1

set.intersection(*map(set,d)) 

Answer 2

for 2.4, you can just define an intersection function.

def intersect(*d):     sets = iter(map(set, d))     result = sets.next()     for s in sets:         result = result.intersection(s)     return result 

---

for newer versions of python:

the intersection method takes an arbitrary amount of arguments

result = set(d[0]).intersection(*d[1:]) 

alternatively, you can intersect the first set with itself to avoid slicing the list and making a copy:

result = set(d[0]).intersection(*d) 

I'm not really sure which would be more efficient and have a feeling that it would depend on the size of the d[0] and the size of the list unless python has an inbuilt check for it like

if s1 is s2:     return s1 

in the intersection method.

>>> d = [[1,2,3,4], [2,3,4], [3,4,5,6,7]] >>> set(d[0]).intersection(*d) set([3, 4]) >>> set(d[0]).intersection(*d[1:]) set([3, 4]) >>>