common element in some lists

[Gribouillis]

Convert to set

>>> L = ["caoutchouc", "metro-boulot-dodo", "yaourth", "automobile"]
>>> set.intersection(*(set(x) for x in L))
{'u', 't', 'o'}

Actually, you can convert only the first one to set

>>> set(L[0]).intersection(*L[1:])
{'u', 't', 'o'}