自定制format

'''format字符串格式化'''
m = '{0}{0}{0}'.format('ok')
print(m)

class Date:
   def __init__(self, year, mon, day):
      self.year = year
      self.mon = mon
      self.day = day

d1 = Date(2021, 4, 29)
n = '{}{}{}'.format(d1.year, d1.mon, d1.day)
n1 = '{0}{0}{0}'.format(d1) # <__main__.Date object at 0x0000021F8C078490> <__main__.Date object at 0x0000021F8C078490> <__main__.Date object at 0x0000021F8C078490>
n2 = '{0.year}{0.mon}{0.day}'.format(d1)
print(n)
print(n1)
print(n2)


'''自定制format'''
# 先定制一个格式字典
format_dic = {
   'ymd': '{0.year}/{0.mon}/{0.day}',
   'm-y-d': '{0.mon}-{0.year}-{0.day}',
   'y:m:d': '{0.year}:{0.mon}:{0.day}'
}

class Date_one:
   def __init__(self, year, mon, day):
      self.year = year
      self.mon = mon
      self.day = day

   def __format__(self, format_spec): # 参数为定制格式字典的key
      if not format_spec or format_spec not in format_dic: # 判断format_spec参数为空和不等于format_dic的key值的情况
         format_spec = 'ymd'
      fm = format_dic[format_spec] # 取到key对应的value，即格式本身
      return fm.format(self) # __format__必须要有返回值，且返回值必须为字符串类型

d2 = Date_one(2021, 4, 30)
print(format(d2))
print(format(d2, 'm-y-d'))
print(format(d2, 'y:m:d'))