>>> from polinomis import Polinomi

>>> p = Polinomi()
>>> p.grau()
0
>>> p[5]
0
>>> p[3] = 2
>>> p[3]
2
>>> p[2] = 7
>>> p[2]
7
>>> p.grau()
3
>>> p[3] = 0
>>> p[3]
0
>>> p.grau()
2