Write a singleton mode
class Stu():
def __new__(cls, *args, **kwargs):
if not hasattr(cls,'inst'):
cls.inst=object.__new__(cls)
return cls.inst
def show(self,name):
self.name=name
zs=Stu('Zhang San')
ls=Stu('Li Si')
print(zs is ls)
print(zs==ls)
__call to write a Fibonacci sequence
class Feibo():
def __init__(self):
pass
def __call__(self,n):
a,b=1,1
lb=[]
if n==1:
lb.append(1)
elif n==2:
lb.append(1)
lb.append(1)
else:
x=1
while x<=n:
lb.append(a)
a,b=b,a+b
x+=1
return lb
a=Feibo()
print(a(5))
3. How to destroy an object
4. Write the method of str
class A():
def __init__(self,name,age):
self.name=name
self.age=age
def __str__(self):
return 'My name is{},This year{}year'.format(self.name,self.age)
def __repr__(self):
return 'Full name{},Age{}'.format(self.name,self.age)
zs=A('Zhang San',19)
ls=A('Li Si',10)
print('%s'%zs)#Call str
print('%r'%ls)#Call repr. When str is not available, call repr by default
5. Hash() function
class A():
def __init__(self,name,age):
self.name=name
self.age=age
def __eq__(self, other):
return self.__dict__==other.__dict__
def __hash__(self):
return hash(self.name)
a=A('Zhang San',19)
b=A('Li Si',20)
c=A('Zhang San',19)
d={a,b,c}
print(a==c)#True
print(a is c)#False, different address
print(d)
issubclass(B, A) determines whether B is A subclass of A
isintance (c,A) judge whether c is an example of class A
enumerate function
a='abc'
for x,y in enumerate(a):
print(x,y)
dir, view available functions
print(dir([].__iter__()))
print(dir({}))
print(dir(()))
#Iterator is to print one by one to reduce memory consumption
a=[1,3,4] b=a.__iter__() print(next(b)) print(b.__next__()) a='123' b=list(a) c=tuple(a) print(c)
Write a Fibonacci sequence by iteration
class Feibo():
def __init__(self,num):
self.num=num
self.current=1
self.a=1
self.b=1
def __iter__(self):
return self
def __next__(self):
if self.current<=self.num:
ret=self.a
self.a,self.b=self.b,self.a+self.b
self.current+=1
return ret
else:
raise StopIteration#Stop iteration
for x in Feibo(5):
print(x)
Generator, yeld generator, the principle is to stop at first, do other things, and then come back
def han():
i=0
while i<10:
yield i
i+=1
b=han()
print(next(b))
print(next(b))
##eg:
def hanshu():
yield 1
yield 2
a=hanshu()
print(next(a))
print(next(a))
##Use of send method
def bingqilin():
a=0
b=yield a
print('b-----',b)
yield 2
yield 3
x=bingqilin()
print(next(x))#0
y=x.send(999)to B Assign 999 and 2 to y
print(y)#2
print(next(x))#3
#send method eg
def jisuan():
get_num=0
count=1
avg=0
total=0
while True:
get_num=yield avg
total=total+get_num
avg=total/count
count+=1
b=jisuan()
next(b)
print(b.send(10))
print(b.send(20))
print(b.send(30))
eg:
def qushu():
for x in 'abc':
yield x
for x in range(5):
yield x
b=qushu()
for i in b:
print(i)
Use of yeld from
def gen():
yield from 'asf'
yield from range(3)
for x in gen():
print(x)
#Expressions for generators
a=[i for i in range(3)] print(a)#[0,1,2] c=(i for i in range(3))#Generator Expressions print(c)
Decorator
Three elements of closure
1. Closure function, must have nested function
2. For embedded functions, the variables of the outer function must be referenced
3. The closure function returns the address of the embedded function (function name)
def hanshu1(tax):
name='Zhang San'
def hanshu2(a,b):
c=(a+b)*tax
return c
print(hanshu2.__closure__)#Judge whether it is a closure function, with call it is a closure
return hanshu2
a=hanshu1(0.2)
y=a(5,6)
print(y)#0.2*(5+6)
b=hanshu1(0.3)
z=b(5,6)
print(z)#0.3*(5+6)
Decorator
import time
def hehe(f):
def haha():
a=time.time()
print('11111')
f()##The meaning of this sentence is to jump back to the modified function, execute the modified function, and then execute the following statement
b=time.time()
print('2222222222',b-a)
return haha
@hehe#The function hs is used to modify hehe, so first find hehe
def hs():
print('start')
he=0
for i in range(5):
he+=1
print('End')
hs()
@hehe##(the meaning of this sentence is to modify the hehe function with hs1, so find the hehe function first.)
def hs1():
print('iiiiiiiii')
print('yyyyyyyyy')
hs1()
#eg:
def decor(f):
def neibu(*args,**kwargs):
print('****')
f(*args,**kwargs)
print('*****')
return neibu
@decor
def yanchanghui(*args,**kwargs):
print(args)
for x in args:
print(x,end=' ')
print()
print(kwargs)
for k,v in kwargs.items():
print(k,v)
print('Vocal concert')
yanchanghui('Lau Andy','Sherry',age=18,address='Guangzhou')
Decorator with return value
def decor(f):
def neibu(name,age):
print('***')#1
r=f(name,age)
print('******')#4
return r#5
return neibu
@decor
def hanshu(name,age):
print(name,age,'Concert')#2
return name+str(age)#3
x=hanshu('Lau Andy',19)
print(x)
eg:
from functools import wraps
def decor(f):
@wraps(f)
def neibu(name,age):
print('***')
r=f(name,age)
print('*****')
return r
return neibu
@decor
def hanshu(name,age):
'''
:param name:
:param age:
:return:
'''
print(name,age,'Concert')
return name+str(age)
x=hanshu('Lau Andy',19)
print(x)
print(hanshu.__doc__)
print(hanshu.__name__)
eg:
def decor1(func):
def neib(name,age):
print('1')
ret =func(name,age)
print('2')
return ret
return neib
def decor2(func):
def neib(name,age):
print('1#')
ret=func(name,age)
print('2#')
return ret
return neib
@decor1
@decor2
def hello(name,age):
print('hello')
return name+str(age)
ret=hello('Lau Andy',19)
print(ret)
property method
class Stu():
def __init__(self,name,age):
self.name=name
self.__age=age
@property
def message(self):
print('I am here')
return self.__age
@message.setter
def message(self,x):
print('11111')
self.__age=x
s=Stu('Zhang San',19)
s.message=29
print(s.message)
print(s.name)
task
1. Iterator exercise
class PrimeNumbers:
def __init__(self, start, end):
self.start = start
self.end = end
def isPrimeNum(self, k):
if k < 2:
return False
for i in range(2, k):
if k % i == 0:
return False
return True
def __iter__(self):
for k in range(self.start, self.end + 1):
if self.isPrimeNum(k):
yield k
for x in PrimeNumbers(1, 10):
print(x)
2. Generator practice
Generator exercises
def read_file(fpath):
BLOCK_SIZE = 6
with open(fpath, 'r') as f:
while True:
block = f.read(BLOCK_SIZE)
if block:
yield block
else:
return
import os
g = read_file(os.getcwd() + '\\aa.txt')
for content in g:
print(content)
3. Decorator practice
from sys import stdout
def forever(fun):
def inner():
print("loop")
while True:
# nonlocal n
n = input("Enter the number of rows in the upper triangle of the diamond:")
if n == "q" or n == "exit":
print("Program exited!")
break
fun(n)
return inner
def verify_number(fun):
def inner(n):
print("Verify the validity of the input")
if isinstance(n, int) or n.isdigit(): # Determine whether the string is composed of pure integer numbers
n = int(n)
fun(n)
else:
print("Please input integer!!!")
return inner
@forever
@verify_number
def print_diamond(n):
for i in range(1, n + 1):
for j in range(1, n - i + 1):
stdout.write(' ')
for k in range(1, 2 * i - 1 + 1):
stdout.write('*')
print()
for i in range(1, n - 1 + 1):
for j in range(1, i + 1):
stdout.write(' ')
for k in range(1, 2 * (n - i) - 1 + 1):
stdout.write('*')
print()
print_diamond()