1.from types import MethodType

MethodType(method,class object)

explain:

bind method to instance of class, only this instance owns method.

2.class.method=methodDefined

explain:

bind method to class, all instances have this method.

3.__slots__ = ('a','b',....)

explain:

restrict the propertys of class, can only have a,b,... of ()

warning: this __slots__ does not affect child class.

if child class has __slots__ too, it will take __slots__ of parent too.

4.class Student(object):

name = 'Student'

>>> s = Student() # 创建实例s

>>> print(s.name) # 打印name属性，因为实例并没有name属性，所以会继续查找class的name属性

Student

>>> print(Student.name) # 打印类的name属性

Student

>>> s.name = 'Michael' # 给实例绑定name属性

>>> print(s.name) # 由于实例属性优先级比类属性高，因此，它会屏蔽掉类的name属性

Michael

>>> print(Student.name) # 但是类属性并未消失，用Student.name仍然可以访问

Student

>>> del s.name # 如果删除实例的name属性

>>> print(s.name) # 再次调用s.name，由于实例的name属性没有找到，类的name属性就显示出来了

Student

explain:

property of class and property of instance of class are different and separate.

5.@property and @name.setter

class Screen(object):

@property

def width(self):

return self._width

@width.setter

def width(self,value):

if not isinstance(value,(int,float)):

raise ValueError('width must be number')

self._width=value

@property

def height(self):

return self._height

@height.setter

def height(self,value):

if not isinstance(value,(int,float)):

raise ValueError('height must be number')

self._height=height

@property

def resolution(self):

return self._width*self._height

explain:

@property is getter, and it takes another property setter with format of name.setter

6.multiple inheritance

7.MixIn

network service class:TCPServer, UDPServer

multiple process and multiple thread:ForkingMixIn, ThreadingMixIn

multiple process TCP server:

class MyTCPServer(TCPServer, ForkingMixIn):

pass

multiple threads UDP server:

class MyUDPServer(UDPServer, ThreadingMixIn):

pass

8.__str__ and __repr__

class s(object):

pass

s1=s()

print(s1) will invoke print(s1.__str__())

s1 will invoke s1.__repr__()

__iter__

class Fib(object):

def __init__(self):

self.a, self.b=0,1

def __iter(self):

return self

def __next__(self):

self.a, self.b=self.b,self.a+self.b

if self.a>100000:

raise StopIteration()

return self.a

for n in Fib():

print(n)

output:

1

1

2

3

....

46368

75025

__getitem__

make instance can be used like list.

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] get 1

f[1] get 1

f[2] get 2

f[3] get 3

f[10] get 89

for slice

class Fib(object):

def __getitem__(self,n):

if isinstance(n,int):

a,b=1,1

for x in range(n):

a,b=b,a+b

return a

if isinstance(n,slice):

start=n.start

stop=n.stop

if start is None:

start=0

a,b=1,1

L=[]

for x in range(stop):

if x>=start:

L.append(a)

a,b=b,a+b

return L

9.enum

from enum import Enum

Month=Enum('M',('Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'))

for name,member in Month.__members__.items():

print(name,'=>',member,','member.value)

Jan => M.Jan , 1

Feb => M.Feb , 2

Mar => M.Mar , 3

Apr => M.Apr , 4

May => M.May , 5

Jun => M.Jun , 6

Jul => M.Jul , 7

Aug => M.Aug , 8

Sep => M.Sep , 9

Oct => M.Oct , 10

Nov => M.Nov , 11

Dec => M.Dec , 12

from enum import Enum, unique

@unique

class Weekday(Enum):

Sun = 0

Mon = 1

Tue = 2

Wed = 3

Thu = 4

Fri = 5

Sat = 6

Weekday(0) => Weekday.Sun

Weekday(1) => Weekday.Mon

...

Weekday(6) => Weekday.Sat

name: Sun, Mon, Tue,...

member: Weekday.Sun, Weekday.Mon,...

value: Weekday.Sun.value(0),.....

10.metaclass

class Field(object):

def __init__(self,name,column_type):

self.name=name

self.column_type=column_type

def __str__(self):

return '<%s:%s>' % (self.__class__.__name__,self.name)

class StringField(Field):

def __init__(self,name):

super(StringField,self).__init__(name,'varchar(100)')

class IntergerField(Field):

def __init__(self,name):

super(IntergerField,self).__init__(name,'bigint')

class ModelMetaclass(type):

def __new__(cls,name,bases,attrs):

if name=='Model':

return type.__new__(cls,name,bases,attrs)

print('Found model: %s' % name)

mappings=dict()

for k,v in attrs.items():

if isinstance(v,Field):

print('Found mapping: %s ==> %s' % (k,v))

mappings[k]=v

for k in mappings.keys():

attrs.pop(k)

attrs['__mappings__']=mappings

attrs['__table--']=name

return type.__new__(cls,name,bases,attrs)

class Model(dict,metaclass=ModelMetaclass):

def __init__(self,**kw):

super(Model,self).__init__(**kw)

def __getattr__(self,key):

try:

return self[key]

except KeyError:

raise AttributeError(r"'Model' object has no attribute '%s'" % key)

def __setattr__(self,key,value):

self[key]=value

def save(self):

fields=[]

params=[]

args=[]

for k,v in self.__mappings__.items():

fields.append(v.name)

params.append('?')

args.append(getarrt(self,k,None))

sql='insert into %s (%s) values (%s)' % (self.__table__, ','.join(fields), ','.join(params))

print('SQL: %s' % sql)

print('ARGS: %s' % str(args))

u = User(id=12345, name='Michael', email='[email protected]', password='my-pwd')

u.save()