Object-oriented advanced - built-in method (2)

七、__setitem__, __getitem__, __delitem__

　　item series

class Foo:
    def __init__(self, name):
        self.name = name

    def __getitem__(self, item):
        # print('getitem...')
        #print(item)

        return self. __dict__ .get(item) #The   dictionary get method will take the value if there is one, and no error will be reported if there is no

    def __setitem__(self, key, value):
        # print('setitem...')
        # print(key,value)
        self.__dict__[key] = value

    def __delitem__(self, key):
        # print('delitem...')
        # print(key)
        # self.__dict__.pop(key)
        del self.__dict__[key]

obj = Foo ( ' egon ' )


# 1. View attributes 
# obj. attribute name 
# The item series is to simulate the object as a dictionary, and you can access 
obj[ ' name ' ]    like a dictionary # complete the effect of obj.name value in this form """

getitem...
name
"""
print(obj['name'])

# 2. Set properties 
# obj.sex = 'male' 
obj[ ' sex ' ] = ' male '

print(obj.__dict__)
print(obj.sex)

# 3. Delete attribute 
# del obj.name 
del obj[ ' name ' ]
 print (obj. __dict__ )
 """
{'sex': 'male'}
"""

 

八 、 __ str__, __repr__, __format__

　　Change the object's string display __str__, __repr__
　　to customize the format string __format__

d = dict({ ' name ' : ' egon ' })
 print (isinstance(d, dict))   # True, d is an instance of class dict 
print (d)

class Foo:
     pass 
obj = Foo()
 print (obj)
 """ is also a print object, the display form is completely different, and printing always hopes to have a prompt function like the previous one.
{'name': 'egon'}
<__main__.Foo object at 0x10401ad68>
"""

# After the __str__ method is defined, the __str__ method under the object will be triggered when the object is printed, and the result of the string will be used as the result of printing. 
class People:
     def  __init__ (self, name, age):
        self.name = name
        self.age = age

    def  __str__ (self):   #Must return a string # print("Trigger __str__ method:") return ' <name:%s,age:%s> ' % (self.name, self.age)
        
         


obj = People('egon', 18)
print(obj)
"""
<name:egon,age:18>
"""

Study __str__

format_dict= {
     ' nat ' : ' {obj.name}-{obj.addr}-{obj.type} ' , #school name-school address-school type 
    ' tna ' : ' {obj.type}:{obj. name}:{obj.addr} ' , #School type:School name:School address 
    ' tan ' : ' {obj.type}/{obj.addr}/{obj.name} ' , #School type/School address/ school name 
}
 class School:
     def  __init__ (self,name,addr,type):
        self.name=name
        self.addr=addr
        self.type=type

    def __repr__(self):
        return 'School(%s,%s)' %(self.name,self.addr)
    def __str__(self):
        return '(%s,%s)' %(self.name,self.addr)

    def __format__(self, format_spec):
        # if format_spec
        if not format_spec or format_spec not in format_dict:
            format_spec='nat'
        fmt=format_dict[format_spec]
        return fmt.format(obj=self)

s1=School('oldboy1','北京','私立')
print('from repr: ',repr(s1))
print('from str: ',str(s1))
print(s1)

'''
str function or print function--->obj.__str__()
repr or interactive interpreter--->obj.__repr__()
If __str__ is not defined, then __repr__ will be used instead of output
Note: The return value of these two methods must be a string, otherwise an exception will be thrown
'''
print(format(s1,'nat'))
print(format(s1,'tna'))
print(format(s1,'tan'))
print(format(s1,'asfdasdffd'))

school class

date_dic={
    'ymd':'{0.year}:{0.month}:{0.day}',
    'dmy':'{0.day}/{0.month}/{0.year}',
    'mdy':'{0.month}-{0.day}-{0.year}',
}
class Date:
    def __init__(self,year,month,day):
        self.year=year
        self.month=month
        self.day=day

    def __format__(self, format_spec):
        if not format_spec or format_spec not in date_dic:
            format_spec='ymd'
        fmt=date_dic[format_spec]
        return fmt.format(self)

d1=Date(2016,12,29)
print(format(d1))
print('{:mdy}'.format(d1))

custom format exercise

class A:
    pass

class B(A):
    pass

print (issubclass(B,A)) # B is a subclass of A, returns True 

a1 = A()
 print (isinstance(a1,A)) # a1 is an instance of A

issubclass和isinstance

 

Nine, slots