python学习第四天笔记整理

一、迭代器及生成器

#迭代器：迭代的工具

#1 什么是迭代：指的是一个重复的过程，每一次重复称为一次迭代，并且每一次重复的结果是下一次重复的初始值
# while True:
# print('=====>')

# l=['a','b','c']
# count=0
# while count < len(l):
# print(l[count])
# count+=1

#2 为什么要有迭代器？
#对于序列类型：str，list，tuple，可以依赖索引来迭代取值，
# 但是对于dict，set，文件,python必须为我们提供一种不依赖于索引的迭代取值的方式-》迭代器

#3 可迭代的对象(下列都是)：obj.__iter__
# name='egon'
# l=[1,2,3]
# t=(1,2,3)
# d={'name':'egon','age':18,'sex':'male'}
# s={'a','b','c'}
# f=open('a.txt','w',encoding='utf-8')
#
# name.__iter__
# l.__iter__
# t.__iter__
# d.__iter__
# s.__iter__
# f.__iter__

#4 迭代器对象（文件是）：obj.__iter__,obj.__next__
# f.__iter__
# f.__next__

#总结：
#1 可迭代对象不一定是迭代器对象
#2 迭代器对象一定是可迭代的对象
#3 调用obj.__iter__()方法,得到的是迭代器对象(对于迭代器对象，执行__iter__得到的仍然是它本身)

# d={'name':'egon','age':18,'sex':'male'}
# d_iter=d.__iter__()

# f=open('a.txt','w',encoding='utf-8')
# f_iter=f.__iter__().__iter__().__iter__().__iter__()
#
# print(f_iter is f)

# d={'name':'egon','age':18,'sex':'male'}
# d_iter=d.__iter__()
#
# print(d_iter.__next__())
# print(d_iter.__next__())
# print(d_iter.__next__())
# print(d_iter.__next__()) #迭代器d_iter没有值了，就会抛出异常StopIteration

# f=open('a.txt','r',encoding='utf-8')
# print(f.__next__())
# print(f.__next__())
# print(f.__next__())
# print(f.__next__())
# f.close()

# l=['a','b','c']
# l_iter=l.__iter__()
#
# print(l_iter.__next__())
# print(l_iter.__next__())
# print(l_iter.__next__())
# print(l_iter.__next__())

# d={'name':'egon','age':18,'sex':'male'}
# d_iter=iter(d) #d_iter=d.__iter__()
#
# #len(obj) 等同于obj.__len__()
#
# while True:
# try:
# print(next(d_iter)) #print(d_iter.__next__())
# except StopIteration:
# break
#
# print('=>>>')
# print('=>>>')
# print('=>>>')
# print('=>>>')

#for循环详解:
#1、调用in后的obj_iter=obj.__iter__()
#2、k=obj_iter.__next__()
#3、捕捉StopIteration异常，结束迭代
# d={'name':'egon','age':18,'sex':'male'}
# for k in d:
# print(k)

#总结迭代器的优缺点：
#优点:
#1、提供一种统一的、不依赖于索引的取值方式，为for循环的实现提供了依据
#2、迭代器同一时间在内存中只有一个值——》更节省内存，

#缺点：
#1、只能往后取，并且是一次性的
#2、不能统计值的个数，即长度

# l=[1,2,3,4,5,6]
# l[0]
# l[1]
# l[2]
# l[0]

# l_iter=l.__iter__()
# # print(l_iter)
# print(next(l_iter))
# print(next(l_iter))
# print(next(l_iter))
# print(next(l_iter))
# print(next(l_iter))
# print(next(l_iter))
# print(next(l_iter))
#
# l_iter=l.__iter__()
# print(next(l_iter))
# print(next(l_iter))
# print(next(l_iter))

# print(len(l_iter))

生成器

#1 什么是生成器：只要在函数体内出现yield关键字，那么再执行函数就不会执行函数代码，会得到一个结果，该结果就是生成器
def func():
print('=====>1')
yield 1
print('=====>2')
yield 2
print('=====>3')
yield 3

#生成器就是迭代器
# g=func()
#
# res1=next(g)
# print(res1)
#
#
# res2=next(g)
# print(res2)
#
#
# res3=next(g)
# print(res3)

#yield的功能：
#1、yield为我们提供了一种自定义迭代器对象的方法
#2、yield与return的区别1：yield可以返回多次值 #2：函数暂停与再继续的状态是由yield帮我们保存的

# obj=range(1,1000000000000000000000000000000000000000000000000000000000000000,2)
# obj_iter=obj.__iter__()
# print(next(obj_iter))
# print(next(obj_iter))
# print(next(obj_iter))
# print(next(obj_iter))
# print(next(obj_iter))

# def my_range(start,stop,step=1):
# while start < stop:
# yield start #start=1
# start+=step #start=3
#
#
# g=my_range(1,5,2)
# print(g)

# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))
# for i in my_range(1,5,2):
# print(i)

#小练习：:tail -f access.log | grep '404'
# import time
# def tail(filepath):
# with open(filepath,'rb') as f:
# f.seek(0,2)
# while True:
# line=f.readline()
# if line:
# yield line
# else:
# time.sleep(0.05)
#
# def grep(lines,pattern):
# for line in lines:
# line=line.decode('utf-8')
# if pattern in line:
# yield line
#
#
# lines=grep(tail('access.log'),'404')
#
# for line in lines:
# print(line)

#了解知识点：yield表达式形式的用法
def eater(name):
print('%s ready to eat' %name)
food_list=[]
while True:
food=yield food_list#food=yield='一盆骨头'
food_list.append(food)
print('%s start to eat %s' %(name,food))

e=eater('alex')

#首先初始化：
print(e.send(None)) # next(e)
#然后e.send:1 从暂停的位置将值传给yield 2、与next一样
print(e.send('一桶泔水'))
print(e.send('一盆骨头'))

二、面向过程编程

#grep -rl 'python' /etc
#补充：os.walk
# import os
# g=os.walk(r'D:\video\python20期\day4\a')
# # print(next(g))
# # print(next(g))
# # print(next(g))
# # print(next(g))
# for pardir,_,files in g:
# for file in files:
# abs_path=r'%s\\%s' %(pardir,file)
# print(abs_path)

#分析一：

# #第一步：拿到一个文件夹下所有的文件的绝对路径
# import os
#
# def search(target): #r'D:\video\python20期\day4\a'
# while True:
# filepath=yield #fllepath=yield=r'D:\video\python20期\day4\a'
# g=os.walk(filepath)
# for pardir, _, files in g:
# for file in files:
# abs_path = r'%s\%s' % (pardir, file)
# # print(abs_path)
# target.send(abs_path)
#
# # search(r'D:\video\python20期\day4\a')
# # search(r'D:\video\python20期\day4')
#
#
# #第二步：打开文件拿到文件对象f
# def opener():
# while True:
# abs_path=yield
# print('opener func--->',abs_path)
#
#
# target=opener()
# next(target) #target.send('xxxx')
#
# g=search(target)
# next(g)
# g.send(r'D:\video\python20期\day4\a')

#分析二：
# 第一步：拿到一个文件夹下所有的文件的绝对路径
import os
def init(func):
def inner(*args,**kwargs):
g=func(*args,**kwargs)
next(g)
return g
return inner

@init
def search(target): # r'D:\video\python20期\day4\a'
while True:
filepath = yield
g = os.walk(filepath)
for pardir, _, files in g:
for file in files:
abs_path = r'%s\%s' % (pardir, file)
#把abs_path传给下一个阶段
target.send(abs_path)

# 第二步：打开文件拿到文件对象f
@init
def opener(target):
while True:
abs_path = yield
with open(abs_path,'rb') as f:
#把(abs_path,f)传给下一个阶段
target.send((abs_path,f))

#第三步：读取f的每一行内容
@init
def cat(target):
while True:
abs_path,f=yield
for line in f:
#把(abs_path,line)传给下一个阶段
res=target.send((abs_path,line))
#满足某种条件，break掉for循环
if res:
break

#第四步：判断'python' in line
@init
def grep(target,pattern):
pattern = pattern.encode('utf-8')
res=False
while True:
abs_path,line=yield res
res=False
if pattern in line:
#把abs_path传给下一个阶段
res=True
target.send(abs_path)

#第五步：打印文件路径
@init
def printer():
while True:
abs_path=yield
print('<%s>' %abs_path)

g=search(opener(cat(grep(printer(),'python')))) #'python' in b'xxxxx'
g.send(r'D:\video\python20期\day4\a')

#面向过程编程：核心是过程二字，过程指的就是解决问题的步骤，即先干什么后干什么。。。。
#基于该思路编写程序就好比设计一条流水线，是一种机械式的思维方式

#优点：复杂的问题流程化、进而简单化
#缺点：可扩展性差
三、三元表达式

1、def my_max(x,y):
if x >= y:
return x
else:
return y

x=10
y=20

# res=x if x >= y else y
# print(res)

name=input('>>: ').strip()

res='Sb' if name == 'alex' else 'NB'
print(res)

2、列表推导式与生成器表达式

def my_max(x,y):
if x >= y:
return x
else:
return y

x=10
y=20

# res=x if x >= y else y
# print(res)

name=input('>>: ').strip()

res='Sb' if name == 'alex' else 'NB'
print(res)

四、递归调用

#递归调用：在调用一个函数的过程中，直接或者间接又调用该函数本身，称之为递归调用
#递归必备的两个阶段：1、递推 2、回溯

# import sys
# print(sys.getrecursionlimit())
# sys.setrecursionlimit(2000)
# print(sys.getrecursionlimit())

# def func(n):
# print('---->',n)
# func(n+1)
#
# func(0)

# def bar():
# print('from bar')
# func()
#
# def func():
# print('from func')
# bar()
#
# func()

# age(5) = age(4) + 2
# age(4) = age(3) + 2
# age(3) = age(2) + 2
# age(2) = age(1) + 2
#
# age(1) = 18

# age(n)=age(n-1)+2 # n > 1
# age(1) = 18 #n = 1

# def age(n):
# if n == 1:
# return 18
# return age(n-1) + 2
#
# res=age(5)
# print(res)

# l=[1,[2,[3,[4,[5,[6,[7,]]]]]]]
#
#
# def func(l):
# for item in l:
# if type(item) is list:
# func(item)
# else:
# print(item)

# def func():
# print('===>')
# func()
#
# func()
五、二分法

,,,,,,,,,] :
print(:],num)

elif num < l[mid_index]:
:mid_index],num)
else:
print()

六、匿名函数

,),

七、内置函数

#了解
# print(abs(-1))

# print(all([1,'a','b',0]))
# print(all([]))

# print(any([None,False,0,1]))
# print(any([]))

# print(bin(11))
# print(hex(11))
# print(oct(11))

# print('xxx'.encode('utf-8'))
# print(bytes('xxx',encoding='utf-8'))

# print(callable(max))

# print(chr(65))
# # print(chr(90))
# # print(chr(39))
# print(ord('A'))
# print(ord('@'))

# import os
# print(dir(os))

# s=set({1,2,3})
# s.add(4)
# print(s)

# s=frozenset({1,2,3}) #不可变集合

# print(hash('xxx'))

# l=[1,2,'a',4]
# print(list(reversed(l)))

# s=slice(1,5,2)
# l=['a','b','c','d','e']
#
# # print(l[1:5:2])
# # print(l[1:5:2])
#
# print(l[s])

# print(vars() is locals())

#面向对象
classmethod
staticmethod
property

hasattr
getattr
setattr
delattr

isinstance
issubclass

object

super

# obj.__dict__() #vars(obj)

#__import__
# choice=input('>>: ')
# print(choice,type(choice))
#
# # import 'time'
# m=__import__(choice)
# m.sleep(10)

#掌握：
#divmod
# print(divmod(10011,25))

#enumerate
# l=['a','b','c']

# for i in l:
# print(l.index(i),i,)

# for i,v in enumerate(l):
# print(i,v)

#eval:
# res=eval('[1,2,3]')
# print(res,type(res))

# res=exec('[1,2,3]')
# print(res)

#pow
# res=pow(2,3,3) # (2 ** 3 )%3
# print(res)

#round
# print(round(3.5))