Python object-oriented advanced programming--Custom classes

1.1   Custom Classes1.1.1   __str__

>>> class Student (object):

... def __init__ (self, name):

... self.name = name

...

>>> s = Student (' Daidai ')

>>> S.name

' Daidai '

>>> Student (' Daidai '). Name

' Daidai '

>>> Print (Student (' Daidai '))-- It's not good to print

<__main__. Student Object at0x2ac5ebc99128>

>>> class Student (object):

... def __init__ (self, name):

... self.name = name

... def __str__ (self):

... return ' Student object (name:%s) '%self.name

...

>>> Print (Student (' Daidai '))

Student Object (Name:daidai)

>>> s = Student (' Daidai ')

>>> S-- pointing to variables, still not good to see

<__main__. Student Object at0x2ac5ebc99160>

>>> S.name

' Daidai '

will be __str__ also point to __repr__

>>> class Student (object):

... def __init__ (self, name):

... self.name = name

... def __str__ (self):

... return ' Student object (name:%s) '% Self.name

... __repr__ = __str__

...

>>> Print (Student (' Daidai '))

Student Object (Name:daidai)

>>> s = Student (' Daidai ')

>>> S.name

' Daidai '

>>> s

Student Object (Name:daidai)

1.1.2   __iter__

if a class wants to be used for the for ... in loop, like a list or a tuple , you must implement a __iter__ () method that returns an iterative object, and then the Python for Loop constantly calls the iteration object's __next__ () method to get the next value of the loop until it exits the loop when the Stopiteration error is encountered.

Take the Fibonacci sequence for example.

>>> class Fib (object):

... def __init__ (self):

... self.a, self.b = 0, 1 # initialize a and b

... def __iter__ (self):

... return Self # returns the iteration object, which is itself an iterative object returned from its own

... def __next__ (self):

... self.a, self.b = self.b, SELF.A + self.b # calculate Next value

... if SELF.A > 10000: # exit loop condition

... raisestopiteration ();

... return SELF.A # returns the next value

...

>>> for N in Fib ():

... print (n)

...

1

1

2

3

5

8

13

21st

34

55

89

144

233

377

610

987

1597

2584

4181

6765

1.1.3   __getitem__

above The Fib instance feels like a list, but it is not possible to take an element by subscript.

You can do it by __getitem__ the method.

>>> class Fib (object):

... def __getitem__ (self, n):

... a, b = 1, 1

... for x in range (n):

... a, B = B, A + b

... return a

...

>>> f = Fib ()

>>> F[0]

1

>>> F[4]

5

>>> f[88]

1779979416004714189

1.1.4   __getattr__

Normally, when we call a method or property of a class, it will be an error if it does not exist.

>>> class Student (object):

... def __init__ (self):

... self.name = ' Daidai '

...

>>> s = Student ()

>>> Print (S.name)

Daidai

>>> Print (S.score)

Traceback (most recent):

File "<stdin>", line 1, in <module>

Attributeerror: ' Student ' object has Noattribute ' score '

plus __getattr__ Dynamic return property value

>>> class Student (object):

... def __init__ (self):

... self.name = ' Daidai '

... def __getattr__ (self, attr):-- python dynamically calls this method when the input score does not exist

... if attr = = ' Score ':

... return 98

...

>>> s = Student ()

>>> S.name

' Daidai '

>>> S.score

98

the __getattr__ return function is also possible

>>> class Student (object):

... def __getattr__ (self, attr):

... if attr = = ' age ':

... return lambda:24

...

>>> s = Student ()

>>> S.age

<functionStudent.__getattr__.<locals>.<lambda> at 0x2ac5ebc8e730>

>>> S.age ()

24

called only if no attribute is found __getattr__ , existing attributes, such as name, are not found in __getattr__ .

>>> class Student (object):

... def __getattr__ (self, attr):

... if attr = = ' age ':

... return lambda:24

... raise attributeerror (' \ ' student\ ' object has no attribute \ '%s\ '%attr)

...

>>>

>>> s = Student ()

>>> S.name

Traceback (most recent):

File "<stdin>", line 1, in <module>

File "<stdin>", line 5, in __getattr__

Attributeerror: ' Student ' object has noattribute ' name '

>>> S.age

<functionStudent.__getattr__.<locals>.<lambda> at 0x2ac5ebc8e488>

>>> S.age ()

24

1.1.5   __call__

the __call__ method can be invoked directly on the instance itself .

>>> class Student (object):

... def __init__ (self, name):

... self.name = name

... def __call__ (self):

... print (' My name is%s. '% self.name)

...

>>> s = Student (' Daidai ')

>>> s

<__main__. Student Object at0x2ac5ebc99748>

>>> S ()-- Direct Instance object invocation

My name is Daidai.

You can determine whether an object can be called by callable

>>>Callable (Student (' Daidai '))

True

>>> callable (max)

True

>>> Callable ((1, 2, 3))

False

>>> callable (' str ')

False

__call__ can also pass in Parameters

>>> class Student (object):

... def __init__ (self, name):

... self.name = name

... def __call__ (Self, others):

... print (' My name is%s,%s '% (Self.name, others))

...

>>>

>>> s = Student (' Daidai ')

>>> s (' so handsome. ')

My name is Daidai and so handsome.

This article is from the "90SirDB" blog, be sure to keep this source http://90sirdb.blog.51cto.com/8713279/1826210

Python object-oriented advanced programming--Custom classes