lambda , sorted , filter , map函数，递归遍历一个目录

1，lambda函数

• lambda只能处理简单的函数

　　

#一个简单的函数
def func(x,y):
    return x+y
#用lambda实现
lambda x,y : x+y

2，sorted排序函数

• sorted函数
  sorted函数是排序的，是排序一个iterable类型的数据，一般的iterable类型的数据都要这个sort方法，sorted函数能自定义排序的规则

  #sorted函数的类型
  sorted(iterable,key=none,reverse=False)
  
  lst = [{"id":1,"name":"shuai","age":25},{"id":3,"name":"xiang","age":18},{"id":2,"name":"aoli","age":27}]
  
  #按年龄排序
  l1 = sorted(lst,key=lambda dic : dic["age"])
  print(l1)
  #按名字首字母排序
  l2 = sorted(lst,key=lambda dic : dic["name"][0])
  print(l2)

   

3，filter函数

• filter函数
  

  通过函数func判断iterable里面的元素是否符合

  #filter(func,iterable)
  
  
  lst = [19,20,18,30,25,17]
  def func(age):
      return age >18
  
  f = filter(func,lst)
  print(f)
  print("__iter__" in dir(f))
  for i in f:
      print(i)

   

 4，map函数

• map映射函数
  

  #map(func,iterable)
  
  lst = [1,5,3,5,4,8,7,9]
  l1 = map(lambda x : x**2,lst)
  print(list(l1))

   

5，递归

　　递归主要特点是自己调用自己，一定要有指定的结束，Python中官方表示的最深递归次数为1000

　　一个递归的死循环　

ceng = 1
def fun(ceng):
    print(ceng)
    fun(ceng+1)
fun(ceng)


运行结果
995
996
997
998Traceback (most recent call last):
  File "E:/python_iteam/LivePython/day6/目录/递归.py", line 26, in <module>
    fun(ceng)
  File "E:/python_iteam/LivePython/day6/目录/递归.py", line 25, in fun
    fun(ceng+1)
  File "E:/python_iteam/LivePython/day6/目录/递归.py", line 25, in fun
    fun(ceng+1)
  File "E:/python_iteam/LivePython/day6/目录/递归.py", line 25, in fun
    fun(ceng+1)
  [Previous line repeated 994 more times]
  File "E:/python_iteam/LivePython/day6/目录/递归.py", line 24, in fun
    print(ceng)
RecursionError: maximum recursion depth exceeded while calling a Python object

 

　　通过递归，遍历一个文件夹里的所有文件

　　

import os
def func(file_dir,ceng):
    
    list = os.listdir(file_dir)#通过os模块，得到目录下面的目录，以list表示
    for file in list:#循环list，区分文件和目录
        file_path = os.path.join(file_dir,file)#得到绝对路径
        if os.path.isdir(file_path):
            print("\t"*ceng+"%s :" %file)
            func(file_path,ceng+1)#递归函数
        else:
            print("\t"*ceng+"%s"%file)

func("F:\\",0)

 

 

6，二分法查找

 

1. 第一种，直接循环
   

   list = [1,3,4,5,6,8,9,10,24,34,45,54,63]
   lift = 0
   right = len(list)
   n = int(input("请输入一个数："))
   while lift < right:
       mid = (lift + right) // 2
       if list[mid] > n:
           right = mid
       elif list[mid] < n :
           lift = mid + 1
       else:
           print("找到了数%s,下标是%s" %(list[mid],mid))
           break
   else:
       print("list里没有这个数")

    

2. 第二种，通过函数递归，建立一个新的list
   

   list = [1,3,4,5,6,8,9,10,24,34,45,54,63]
   lift = 0
   right = len(list)
   n = int(input("请输入一个数："))
   def func(list,n):
       lift = 0
       right = len(list)
       mid = (lift + right)//2
       if mid > 0:
           if list[mid] > n:
               new_list = list[:mid]
               func(new_list,n)
           elif list[mid] < n:
               new_list = list[mid+1:]
               func(new_list,n)
           elif list[mid] == n:
               print("找到了数%s" %list[mid])
       else:
           print("找不到")
   func(list,n)

    

3. 第三种，通过函数递归，给出左右
   

   list = [1,3,4,5,6,8,9,10,24,34,45,54,63]
   lift = 0
   right = len(list)
   n = int(input("请输入一个数："))
   
   def func(list,lift,right,n):
       mid = (lift+right)//2
       if lift < right:
           if list[mid] > n:
               right = mid
               func(list, lift, right, n)
           elif list[mid] < n :
               lift = mid+1
               func(list, lift, right, n)
           elif list[mid] == n :
               print("找到了%s,位置%s" %(list[mid],mid))
       else:
           print("没找到")
   func(list,lift,right,n)