从项目创建dict：

>>> dict(product) # create a dict from all populated values
{'price': 1000, 'name': 'Desktop PC'}

从dicts创建项目：

>>> Product({'name': 'Laptop PC', 'price': 1500})
Product(price=1500, name='Laptop PC')

>>> Product({'name': 'Laptop PC', 'lala': 1500}) # warning: unknown field in dict
Traceback (most recent call last):
    ...
KeyError: 'Product does not support field: lala'