Python中面向对象你应该知道的一下知识

> a = [1,2,3]
> b = [1,2,3]
> a == b
True
# a和b是否是同一个对象
> a is b
False
# a和b的地址其实是不一样的
> id(a)
4498717128
> id(b)
4446861832

> a = -5
> b = -5
> a == b
True
> a is b
True
> a = -6
> b = -6
> a == b
True
> a is b
False

> a='123'
> b='123'
> a==b
True
> a is b
True
> id(a)
4446903800
> id(b)
4446903800
> x = 'long char'
> y = 'long char'
> x == y
True
> x is y
False

import datetime
> today = datetime.date.today()
> today
datetime.date(2019, 7, 7)
> print(today)
2019-07-07
> str(today)
'2019-07-07'
> repr(today)
'datetime.date(2019, 7, 7)'

> now = datetime.date(2019, 7, 7)
> now
datetime.date(2019, 7, 7)

> a = [1,2,3]
> b = list(a)
> a[1]=200
> a
[1, 200, 3]
> b
[1, 2, 3]

> a = [[1,2,3],[4,5,6],[7,8,9]]
> b = list(a)
> a == b
True
> a is b
False

> a[1][2]='x'
> a
[[1, 2, 3], [4, 5, 'x'], [7, 8, 9]]
> b
[[1, 2, 3], [4, 5, 'x'], [7, 8, 9]]

> import copy
> a = [[1,2,3],[4,5,6],[7,8,9]]
> b = copy.deepcopy(a)
> a
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
> b
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
> a[1][2]='change'
> a
[[1, 2, 3], [4, 5, 'change'], [7, 8, 9]]
> b
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# 定义了基类Base
> class Base:
	def foo(self):
		raise NotImplemented
	def bar(self):
		raise NotImplemented

# 定义实现类
> class Concrete(Base):
	def foo(self):
		print('called foo')
  
  # 实现类并没有实现bar方法
	
> c = Concrete()
> c.foo()
called foo
> c.bar()
Traceback (most recent call last):
 File "<pyshell#391>", line 1, in <module>
  c.bar()
 File "<pyshell#384>", line 5, in bar
  raise NotImplemented
TypeError: exceptions must derive from BaseException

from abc import ABC
# 定义基类，继承于ABC
> class Base(ABC):
	@abstractmethod
	def foo(self):
		pass
	@abstractmethod
	def bar(self):
		pass

	
> class Concrete(Base):
	def foo(self):
		print("called foo")
	# 实现类并没有实现bar方法

> c = Concrete()
Traceback (most recent call last):
 File "<pyshell#357>", line 1, in <module>
  c = Concrete()
TypeError: Can't instantiate abstract class Concrete with abstract methods bar

> from collections import namedtuple
> Point = namedtuple('Point','x y z')
> p = Point(1,3,5)
> p
Point(x=1, y=3, z=5)
> p.x
1
> p.y = 3.5
AttributeError: can't set attribute
# 可以看出通过namedtuple定义对象，就是一个class类型的
> type(p)
<class '__main__.Point'>

# 转化为dict
> p._asdict()
OrderedDict([('x', 1), ('y', 3), ('z', 5)])
# 更新或替换某个属性值
> p._replace(x=111)
Point(x=111, y=3, z=5)
# 使用_make创建新对象
> Point._make([333,666,999])
Point(x=333, y=666, z=999)

> class Cat:
	num_legs = 4
	
> class Cat:
	num_legs = 4
	def __init__(self,name):
		self.name = name

> tom = Cat('tom')
> jack = Cat('jack')
> tom.name,jack.name
('tom', 'jack')
> tom.num_legs,jack.num_legs
(4, 4)
> Cat.num_legs
4

> Cat.num_legs = 6
> tom.num_legs,jack.num_legs
(6, 6)
> tom.num_legs = 2
> tom.num_legs,jack.num_legs
(2, 6)
> Cat.num_legs
6

> class MyClass:
	def method(self):
		print(f"instance method at {self}" )
	@classmethod
	def classmethod(cls):
		print(f'classmethod at {cls}')
	@staticmethod
	def staticmethod():
		print('staticmethod')

		
> mc = MyClass()
> mc.method
<bound method MyClass.method of <__main__.MyClass object at 0x10c280b00
> mc.classmethod
<bound method MyClass.classmethod of <class '__main__.MyClass'
> mc.staticmethod
<function MyClass.staticmethod at 0x1090d4378>

> mc.method()
instance method at <__main__.MyClass object at 0x10910ada0>
> MyClass.method(mc)
instance method at <__main__.MyClass object at 0x10910ada0>

> MyClass.classmethod()
classmethod at <class '__main__.MyClass'>
> MyClass.staticmethod()
staticmethod