Merging lists according to the first element

Question

So I have three lists:

lst1 = [(\'test1\', 0.2), (\'test7\', 0.2)]
lst2 = [(\'test1\', 5.2), (\'test2\', 11.1), (\'test7\', 0.2)]
lst3 = [(\'test1\', 19.2), (