Question

I am using Python 2.5.4. From here: Python -Intersection of multiple lists?

I have this:

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

The following works as expected:

intersect([1,2,3,4], [2,3,4], [3,4,5,6,7])

But, I have something that looks more like the following:

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

If I call it like:

intersect(d)

I get:

TypeError: list objects are unhashable

How do I transform the d above into something intersect() can take?

Answer 1

You need to pass the contents of your list as separate parameters:

intersect(*d)

What happens otherwise is that the whole list is being used as one set instead. The *d syntax indicates to Python that you want to use d as a sequence of parameters to the function, instead using the whole d list as just one parameter.