isinstance和issubclass，__getattribute__，__getitem__,__setitem__,delitem__,__str__（三十五）

 

isinstance(obj,cls)检查是否obj是否是类 cls 的对象

issubclass(sub, super)检查sub类是否是 super 类的派生类

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

class SubFoo(Foo):
    def __init__(self):
        pass

f1 = Foo(2)
print(isinstance(f1,Foo)) # True
print(issubclass(SubFoo,Foo))  # True

 

__getattribute__

当__getattribute__与__getattr__同时存在,只会执行__getattrbute__,除非__getattribute__在执行过程中抛出异常AttributeError

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

    def __getattribute__(self, item):
        print('不管是否存在,我都会执行')

f1=Foo(10)
f1.x
f1.xxxxxx

class Foo:
    def __init__(self,x):
        self.x = x
    def __getattr__(self, item):
        print("执行__getattr...")
        #return self.__dict__[item]
    def __getattribute__(self, item):
        print("不管是否存在，都会执行__getattribute...")
        raise AttributeError("%s not exit" %(item))

class SubFoo(Foo):
    def __init__(self):
        pass

f1 = Foo(2)
f1.x
f1.y

'''
不管是否存在，都会执行__getattribute...
执行__getattr...
不管是否存在，都会执行__getattribute...
执行__getattr...
'''

 

item

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

    def __getitem__(self, item):
        print('__getitem__')
        return self.__dict__[item]
    def __setitem__(self, key, value):
        print('__setitem__')
        self.__dict__[key] = value
    def __delitem__(self, key):
        print('__delitem__')
        self.__dict__.pop(key)

f = Foo('lisi')
print(f.__dict__) # {'Name': 'lisi'}
f['age'] = 18 # __setitem__
print(f.__dict__) # {'Name': 'lisi', 'age': 18}

print(f['Name']) # __getitem__ lisi

del f['age'] # __delitem__

 

__str__,__repr__,__format__

改变对象的字符串显示__str__,__repr__

自定制格式化字符串__format__

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

    def __str__(self):
        return self.name

scl = School("CPU")
print(scl) # CPU

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

    # def __str__(self):
    #     return self.name

scl = School("CPU")
print(scl) # <__main__.School object at 0x000001D071CF5A58>

format_dict={
    'nat':'{obj.name}-{obj.addr}-{obj.type}',#学校名-学校地址-学校类型
    'tna':'{obj.type}:{obj.name}:{obj.addr}',#学校类型:学校名:学校地址
    'tan':'{obj.type}/{obj.addr}/{obj.name}',#学校类型/学校地址/学校名
}
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函数或者print函数--->obj.__str__()
repr或者交互式解释器--->obj.__repr__()
如果__str__没有被定义,那么就会使用__repr__来代替输出
注意:这俩方法的返回值必须是字符串,否则抛出异常
'''
print(format(s1,'nat'))
print(format(s1,'tna'))
print(format(s1,'tan'))
print(format(s1,'asfdasdffd'))

format_time = {
    'YMD':'{0.year}{0.month}{0.day}',
    'Y-M-D':'{0.year}-{0.month}-{0.day}',
    'Y:M:D':'{0.year}:{0.month}:{0.day}',
}

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 format_time:
            format_spec = 'YMD'
        return format_time[format_spec].format(self)

d = Date(2019, 3, 2)
print(format(d, 'Y-M-D')) # 2019-3-2
print(format(d, 'Y:M:D')) # 2019:3:2