@classmethod隐含参数cls, 主要用在需要创建对象的情况，比如多个构造函数的情况，相当于C++重载
@staticmethod没有隐含参数，主要用在需要创建对象的情况，比如参数验证
class Date(object):
def __init__(self, day=0, month=0, year=0):
self.day = day
self.month = month
self.year = year
@classmethod
def from_string(cls, date_as_string):
day, month, year = map(int, date_as_string.split('-'))
date1 = cls(day, month, year)
return date1
@staticmethod
def is_date_valid(date_as_string):
day, month, year = map(int, date_as_string.split('-'))
return day <= 31 and month <= 12 and year <= 3999
date2 = Date.from_string('11-09-2012')
is_date = Date.is_date_valid('11-09-2012')
https://stackoverflow.com/questions/12179271/meaning-of-classmethod-and-staticmethod-for-beginner
