Grouping pairs - suggested tools

[Astley Le Jasper]

I have a list of tuples that indicate a relationship, ie a is related
to b, b is related to c etc etc. What I want to do is cluster these
relationships into groups.  An item will only be associated with a
single cluster.

Before I started, I wondered if there was any particular tool within
Python I should be looking at. I don't expect anyone to code this for
me, just say ... "you need to look at using x". I was going to use
populate a dictionary and

Sorry for being so vague.

Example Data:
[(a,b)
(a,c)
(a,d)
(b,c)
(b,d)
(c,d)
(e,f)
(e,g)
(f,g)
(h,i)]

Output (grouping id, item ref)
(1,a),
(1,b),
(1,c),
(1,d),
(2,e),
(2,f),
(2,g),
(3,h),
(3,i)