python find root/parent based on list of tuples -

suppose have list of tuples in store keys (strings):

l=[     (a,b),     (b,c),     (c,d),     (d,e),     (e,f),     (w,x),     (w,t),     (t,q),     (q,r),     (q,u),  ] 

how can find relations (especially head) between tuples in list, eg:

a<-b<-c<-d<-e<-f w<(-x,t-<q-<(r,u)) 

so know f grand grand grand grand child of a?

regards js.

we'll have dictionary mapping names tonodes, , build nodes trees.

from collections import defaultdict class node:     def __init__(self):         children = []     def add_child(self, child):         self.children.append(child)     def ancestor_of(self, descendant):         if self == descendant:             return [self]         child in children:             c=child.ancestor_of(descendant)             if c:                 return [self, *c]         return none  node_dict = defaultdict(node) fst, snd in l: #assuming , b strings     d[fst].add_child(d[snd]) #query trees using ancestor_of