I have a list as a input made from tuples where the origin is the 1st object and the neighbour is the 2nd object of the tuple. for example :

inp : lst = [('a','b'),('b','a'),('c',''),('a','c')]
out : {'a': ('a', ['b', 'c']), 'b': ('b', ['a']), 'c': ('c', [])}

first i tried to cast the list into a dictonary, like this

dictonary = dict(lst)

but i got an error say that

dictionary update sequence element #0 has length 1; 2 is required

The simplest is probably inside a try / except block:

lst = [('a','b'),('b','a'),('c',''),('a','c')]out = dict()for k, v in lst:try:if v != '':out[k][1].append(v)else:out[k][1].append([])except KeyError:if v != '':out[k] = (k, [v])else:out[k] = (k, [])print out

Which gives:

{'a': ('a', ['b', 'c']), 'b': ('b', ['a']), 'c': ('c', [])}