python的魔术方法 __format__

__format__()方法

　　__format__()传参方法：someobject.__format__(specification)

　　specification为指定格式，当应用程序中出现"{0:specification}".format(someobject)或format(someobject, specification)时，会默认以这种方式调用

　　当specification为" "时，一种合理的返回值是return str(self),这为各种对象的字符串表示形式提供了明确的一致性

　　注意，"{0!s}".format()和"{0!r}".format()并不会调用__format__()方法，他们会直接调用__str__()或者__repr__()

　　例：自定义我们自己的__format__()格式

#coding=utf-8

class formatest:
    def __init__(self, name, age):
        self.name,self.age = name, age

    def __format__(self,specification):
        if specification == "":
            return str(self)

        strformat = specification.replace("%s",self.name).replace("%r",self.age)
        return strformat

if __name__ == "__main__":
    people = formatest("zhanglin", "31")
    print ("{}".format(people))
    print ("{0:%s-%r}".format(people))
    print (format(people, "%s-%r"))
    

　　例：格式化对象中的集合

#coding=utf-8

class people:
    def __init__(self, name, age):
        self.name,self.age = name, age

    def __format__(self,specification):
        if specification == "":
            return str(self)

        strformat = specification.replace("%s",self.name).replace("%r",self.age)
        return strformat

class hand:
    def __init__(self, *people):
        self.peoples = []
        self.peoples= list(people)
    def __format__(self, specification):
        if specification == "":
            return str(self)        
        return ",".join("{:{fs}}".format(c, fs=specification) for c in self.peoples)
  
if __name__ == "__main__":
    handobj = hand(people("zhangsan", "18"), people("lisi", "28"), people("zhanglin", "38"))
    print ("{:%s-%r}".format(handobj))