High order reflection, magic class method day28

A, issubclass and isinstance

issubclass: determining the first parameter is not the second sub-type of parameter returns True or False

# issubclass

class Foo:
    pass
class Bar(Foo):
    pass
class Tt(Bar):
    pass
print(Bar.__bases__)
print(issubclass(Bar, Foo))
print(issubclass(Tt, objcet)

isinstance: determining the first parameter is not the second object parameters, return True or False

class Foo:
    pass
class Tt():
    pass

f = Foo()
print(isinstance(f, Foo))
print(isinstance(f, Tt))

Second, reflection

Reflection: is acquired by a string, setting, deleting object property or method

hasattr (): determining whether an attribute in an object, returns True or False

getattr (): get property methods or string, if acquired, it will return the corresponding property or method

setattr (): method to set properties or string

delattr (): method to delete an attribute or a string

class Foo:
    def run(self):
        print('run')
    def speak(self):
        print('speak')

p = Foo()
print(Foo.__dict__)
cmd = input('请输入命令：')

# 方案一：
print(Foo.__dict__[cmd])
Foo.__dict__[cmd](p)

# 方案二：
if hasattr(p, cmd):
    run = getattr(p, cmd)
    run()
else:
    print('该命令不存在')

# 通过用户输入key和value往对象中赋值
p = Foo()
key = input('请输入key：')
value = input('请输入value：')
setattr(p, key, value)
print(p.age)

# 动态的往对象中放方法
def test(a):
    print(a)
print(p.__dict__)
setattr(p, 'test', test)
print(p.__dict__)
p.test(0)

# 动态删除p中属性为变量a的属性
p.name = 'lqz'
p.age = 19
p.sex = 'male'
a = input('请输入要删除的属性：')
print(p.__dict__)
delattr(p, a)
print(p.__dict__)

Third, the built-in method

__str__: Rewrite print after print is __str__ return value without rewriting the return of the memory address of the object

__repr__ similar with str, direct write the variable name in an interactive command, execute __repr__

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

f = Foo('nick')
# print(f.__str__())
print(f)  # 相当于上面那句

__setattr__, __delattr__, __getattr__

Point intercept method:

If you go to fetch the object attributes, once to get any, will enter into __getattr__

If you object to assign attributes (add or modify), will enter into __setattr__

If the attribute deleted object, will enter __delattr__

class Foo:
    def __init__(self, name):
        self.name = name
    def __getattr__(self, item):
        return '你傻逼阿， 没有这个字段'
    def __setattr__(self, key, value):
        # self.key = value   无限递归
        self.__dict__[key] = value
    def __delattr__(self, item):
        # del self.item    无限递归
        self.__dict__.pop(item)
f1 = Foo(10)

When __item__ series of objects by [] brackets value assignment, remove the value of calls

class Foo：
    def __init__(self, name):
        self.name = name
    def __getitem__(self, item):
        name = getattr(self, item)
    def __setitem__(self, key, value):
        print('obj[key]=lqz赋值时，执行我')
        self.__dict__[key] = value
    def __delitem__(self, key):
         print('del obj[key]时，执行我')
         self.__dict__.pop(key)

__call__: Object brackets will call it

class Foo:
    def __call__(self):
        print('xxxx')
        
f = Foo()
f()

__enter__ and __exit__

Context Manager

Fourth, breakpoint debugging

First-class citizens: as long as it can be assigned to a variable thing, this thing called first-class citizens

Where you want to add breakpoint with a mouse click it, you'll see a red circle
where the red, to the implementation of the program will be suspended
before the power failure should be loaded error
green arrow indicates quickly jump to a breakpoint execution

Console error, click on the last line you can read, the cursor will quickly locate the error code, put on the error code, plus power, breakpoint debugging