Python3 the custom class

　　Such __slots__ see similar shaped like __xxx__ variable or function name it should be noted that these are special purpose in Python

　　Python There are many special-purpose functions that can help us custom class

　　__str__

　　Student define a class, an instance of printing

>>> class Student(object):
...     def __init__(self,name):
...         self.name=name
... 
>>> print(Student('Zhangsan'))
<__main__.Student object at 0x7f8a4830a748>

　　Print out <__ main __. Student object at 0x7f8a4830a748> does not look good, non-intuitive

　　How nice to print it? Only you need to define __str __ () method to return a nice string on it

>>> class Student(object):
...     def __init__(self,name):
...         self.name=name
...     def __str__(self):
...         return 'Student object(name:%s)' % self.name
... 
>>> 
>>> print(Student('Zhangsan'))
Student object(name:Zhangsan)

　　Examples of such print out, not only good-looking, and is easy to see inside instance important data

　　But if the direct knock variables in the terminal instead of print, or print out the same does not look good

>>> Student('Zhangsan')
<__main__.Student object at 0x7f8a4830a8d0>

　　This is because the call is not directly displayed variables __str__(), but __repr__(), the difference is __str__()returned to the user to see the string and __repr__()returns a string program developers to see, that is, __repr__()for debugging services.

The solution is to define a second __repr__(). But usually __str__(), and __repr__()the code is the same, so there is a lazy wording:

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

　　

　　__iter__

　　If you want a class to be used in for..in loops, similar to that list or tuple, you must implement a __iter __ () method, which returns an iterator object, and then, Python for loop iteration will continue to call the object __next __ () method to get the next cycle of value, until it encounters an error StopIteration exit the loop

Fib class (Object): 
    DEF __init __ (Self): 
        # initialize two counters 
        self.a, self.b = 0, 1 
    DEF the __iter __ (Self): 
        # iteration object instance itself, to return to their 
        return Self 
    DEF the __next __ (Self) : 
        self.a, self.b, self.b, =, + self.b, self.a 
        # set loop exit condition 
        IF self.a> 10000: 
            The raise the StopIteration () 
        return self.a 

for in n-Fib (): 
    Print (n- )

　　Export

>>> for n in Fib():
...     print(n)
...
1
1
2
3
5
...
46368
75025

　　

　　__grtitem__

　　Examples Although Fib can function in a for loop, and looks somewhat like a list, however, to use it as a list or not, for example, take the first 5 elements

>>> Fib()[5]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'Fib' object is not subscriptable

　　To remove the above list as performance index of the element in accordance with the need to achieve the __getitem __ () method 

　　special_getitem.py

class Fib(object):
    def __getitem__(self,n):
        a,b=1,1
        for x in range(n):
            a,b=b,a+b
        return a

　　Now, you can press any number to access the column marked one of the

>>> f[0]
1
>>> f[1]
1
>>> f[100]
573147844013817084101

　　However, there is a list of methods corresponding to the slice error determined Fib

>>> f[1:5]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in __getitem__
TypeError: 'slice' object cannot be interpreted as an integer