python format自定义格式化

# #自定义格式化
# format_dic={
#     'ymd':'{0.year}{0.mon}{0.day}',
#     'm-d-y':'{0.mon}-{0.day}-{0.year}',
#     'y:m:d':'{0.year}:{0.mon}:{0.day}'
# 
# }
# 
# class Date:
#     def __init__(self,year,mon,day):
#         self.year=year
#         self.mon=mon
#         self.day=day
# 
#     def __format__(self, format_spec):
#         print('执行了')
#         print('-->',format_spec)
#         if not format_spec or format_spec not in format_dic:
#             format_spec='ymd'
#         fm=format_dic[format_spec]
#         return fm.format(self)
# d1=Date(2018,7,26)
# # format(d1)
# print(format(d1,'m-d-y'))
# print(format(d1,'y:m:d'))
# print(format(d1,'m-d--y'))
# print(format(d1))