resultats = {'Dupont':{'DS1' : [15.5, 4],
                       'DM1' : [14.5, 1],
                       'DS2' : [13, 4],
                       'PROJET1' : [16, 3],
                       'DS3' : [14, 4]},
             'Durand':{'DS1' : [6 , 4],
                       'DM1' : [14.5, 1],
                       'DS2' : [8, 4],
                       'PROJET1' : [9, 3],
                       'IE1' : [7, 2],
                       'DS3' : [8, 4],
                       'DS4' :[15, 4]}}


def moyenne(nom):
    if nom in ...:
        notes = resultats[nom]
        total_points = ...
        total_coefficients = ...
        for ...  in notes.values():
            note , coefficient = valeurs
            total_points = total_points + ... * coefficient
            total_coefficients = ... + coefficient
        return round( ... / total_coefficients , 1 )
    else:
        return -1