def find_element(e, l):
    """ return the positions of e in l as a list of 2-tuples
    l must be a list of sublists.
    e is an element potentially present in the sublists. 
    find_element(1, [[3,2,1],[4],[0,1]]) -> [ (0,2), (2,1) ]
    find_element(1, []) -> []
    find_element(1, [ [1,1], [1] ]) -> [ (0,0), (0,1), (1,0) ] 
    """
    return [(i, j) for i, ll in enumerate(l) for j, ee in enumerate(ll) if e == ee]