Python3 Learning Notes Custom class

__str__

class Student (object):     def __init__ (self, name):         = name    def__str__(self):        return'  Student Object (name:%s)' % self.name __repr__ = __str__

#作用: Internal information can be printed directly
Print (Student ('Michael')) Student object (Name:michael)

__getattr__

When a non-existent property is called, for example score , the Python interpreter attempts to invoke __getattr__(self, ‘score‘) the property, so that we have a chance to return score the value:

classStudent (object):def __init__(self): Self.name='Michael'    def __getattr__(self, attr):ifattr=='score':            return99

>>> s =Student ()
>>> S.name
'Michael'
>>> S.score
     about

#返回函数也是完全可以的:
Class  Student (object):    def__getattr__(self, attr):        if attr=='age':            returnLambda: 25
Just call the method to change to:
>>> S.age ()
25

Any call s.abc will be returned None , because the default return that we define is __getattr__ None . To allow class to respond to only a few specific properties, we are going to throw the error according to the Convention AttributeError :

class Student (object):     def __getattr__ (self, attr):         if attr=='age':            returnLambda: 25        raise attributeerror ('\ ' student\ ' object has no attribute \ '%s\ ' % attr

This actually allows all the properties and method invocations of a class to be dynamically processed, without any special means.

Action Example:

With completely dynamic __getattr__ , we can write a chain call:

classChain (object):def __init__(Self, path="'): Self._path=Pathdef __getattr__(self, path):returnChain ('%s/%s'%(Self._path, path))def __str__(self):returnSelf._path__repr__=__str__




>>> Chain (). Status.user.timeline. List
'/status/user/timeline/list '
In this way, regardless of the API changes, the SDK can be based on the URL to achieve a full dynamic call, and not with the increase of the API to change!

__call__

In any class, you can simply __call__() invoke the instance by defining a method.

class Student (object):     def __init__ (self, name):         = name    def__call__(self):        print('My Name is%s. ' % self.name)


The method is called as follows:
>>> s = Student (' Michael ')
# Self parameter do not pass in
Is Michael.

Python3 Learning Notes Custom class