>>> from delegats import percent_nuls

>>> d =  {'Anna': 3, 'Arnau':0, 'Enric': 5, 'Josep': 1,
... 'Pol': 1, 'Roger': 2, 'Zaira': 0, 'nuls': 1}
>>> print("{:.2f}".format(percent_nuls(d)))
7.69