python 的文件操作与函数（三）

Python学习

一： Python的 文件操作
二： Python的 函数
三： Python函数的局部变量

1. Python的 文件操作

• 1.1 读文件

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
f = open("yesterday","r",encoding="utf-8") # 打开文件
data = f.read()
print(data)

• 1.2 文件的写

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
f = open("yesterday1","w",encoding="utf-8") # 打开文件
f.write("zhangyy")
f.write("anebi")

• 1.3 文件的追加

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
f = open("yesterday1","a",encoding="utf-8") # 打开文件
f.write("homeupdate,")
f.write("yangyang")
print(f)

• 1.4 读取文件的前几行

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
# f = open("yesterday","r",encoding="utf-8").read()
f = open("yesterday","r",encoding="utf-8")
for i in range(6):
     print(f.readline())

• 1.5 分割线取值一

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
f = open("yesterday","r",encoding="utf-8")
for index,line in enumerate(f.readlines()):
      if index == 9:
          print('----分割线-----')
          continue
      print(line.strip())

• 1.6 分割线取值二

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
f = open("yesterday","r",encoding="utf-8")
count = 0
for line in f:
    if count == 9:
        print("----分割线-----")
        count +=1
        continue
    print(line)
    count +=1

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
f = open('yesterday','r',encoding='utf-8')
print(f.tell()) ### 定位标示符
print(f.read(5))
print(f.tell())
print(f.seek(0))  ### 光标返回

• 1.7 进度条的书写

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
import sys
import time
'''
f = open("yesterday2","w",encoding="utf-8") # 打开文件
f.write("hello1,\n")
f.write("hello2,\n")
'''
for i in range(20):
    sys.stdout.write("#")
    sys.stdout.flush()
    time.sleep(0.1)

• 1.8 截断文件

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
f = open("yesterday3","a",encoding="utf-8")
f.seek(10)
f.truncate(20)

• 1.9 读写文件

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
 f = open("yesterday2","r+",encoding="utf-8") # 读写文件
g = open("yesterday4",'w+',encoding="utf-8") # 写读文件
t = open("yesterday4",'a+',encoding="utf-8") # 追加读写
y = open("yesterday4",'rb') ## 以二进制的读写
r = open("yesterday4",'wb') ### 以二进制的方式写读
z = open("yesterday4",'wb') ### 以二进制的方式追加读写
r.write("hello binary\n".encode())
r.close()
'''
g.write("spark,\n")
g.write("spark,\n")
print(g.readline())
print(g.readline())
g.seek(5)
g.write("------hadoop-------")
print(g.readline())
g.seek(5)
'''

• 1.9 with 读写打开 文件

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
with open("yesterday","r",encoding="utf-8") as f:
   for line in f:
    print(line)
    # print(f.readline())

二： Python的函数

• 2.1 Python的函数

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
### 函数
def func1():
    print('in thi func1')
    return 0
# 过程  ---- 过程就是没用返回值的函数
def func2():
    print("in the func2")
x = func1()
y = func2()
print("from funcl return is %s" %x)
print('from fun2 return is %s' %y)

• 1.2 Python的返回值

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
def test1():
    pass
def test2():
    return 0
def test3():
    return 0,'hello',['a','b','c'],{'name':'alex'}
x=test1()
y=test2()
z=test3()
print(x)
print(y)
print(z)   
### python 的返回值最后 把所有的返回值 放到一个元组里面
#### 函数的返回值：
#### 默认没有返回值就是 none 
#### 返回值 = 1  默认的返回值 就是 一个object （对象）
#### 返回值 > 1  默认返回值就是就是一个元组 （tuple） 

• 1.3 python 的形式调用

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
def test(x,y,z):
    print(x)
    print(y)
    print(z)
# test(y=2,x=1) #与形参顺序无关
# test(1,2)  #与形参一一对应
#test(x=2,3)
test(3,z=2,y=6)

• 1.4 python的默认参数用途

def conn(host,port=3306):
    pass
### #默认参数特点：调用函数的时候，默认参数非必须传递

• 1.4 取元组列表

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
def test1(x,*args):
    print(x)
    print(args)
test1(1,2,3,4,5,6,7)#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
#*args: 接收N 个 位置参数，转换成元组的方式
#*kwargs:接收N 关键字参数，转换成字典的方式
def test1(x,*args):
    print(x)
    print(args)
test1(1,2,3,4,5,6,7)
def test2(**kwargs):
    print(kwargs)
    print(kwargs['name']) ### 取值
test2(name="zhangyy",age="8",sex = "boy")
#test2(**{'name':'alex','age':8})
def test3(name,**kwargs):
    print(name)
    print(kwargs)
test3("alex",age =18,sex="boy")
def test4(name,age =18,**kwargs):
    print(name)
    print(age)
    print(kwargs)
test4("alex",sex="boy")
def test5(name,age=18,*args,**kwargs):
    print(name)
    print(age)
    print(args)
    print(kwargs)
test5('zhangyy',age=34,sex='boy',hobby='wtt')

三：Python函数的局部变量

• 3.1 局部变量

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
def change_name(name):
    print("before change",name)
    name = "flyfish"     #### 局部变量问题 ，只在函数内生效。
    print("after change",name)
name = "zhangyy"
change_name(name)
print(name)

• 3.2 局部变量提权

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
school = "edu,oldboy"
def change_name(name):
    global school   #### 更改 局部变量的 提权问题
    school = "mage linux"
    print("before change",name,school)
    name = "flyfish"
    age = 23
    print("after change",name)
name = "zhangyy"
change_name(name)
print(name)
print(school)
#### 不应该在函数里面改全局变量，特殊情况下才使用，一般不用

• 3.3 列表调用

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
bigdata = ["spark","hadoop","hue","oozie"]
def change_name():
    bigdata[0] = "zookeeper"
    print(bigdata)
change_name()
print(bigdata)
#### 列表，集合， 字典 ，包括 类都可以修改

• 3.4 函数的递归

递归的特性
1. 必须有一个明确的结束条件
2. 每次进入更深一层递归时，问题规模相比上次递归都应有所减少
3. 递归效率不高，递归层次过多会导致栈溢出（在计算机中，函数调用是通过栈（stack）这种数据结构实现的，每当进入一个函数调用，栈就会加一层栈帧，每当函数返回，栈就会减一层栈帧。由于栈的大小不是无限的，所以，递归调用的次数过多，会导致栈溢出）

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
data = [1, 3, 6, 7, 9, 12, 14, 16, 17, 18, 20, 21, 22, 23, 30, 32, 33, 35]
def binary_search(dataset, find_num):
    print(dataset)
    if len(dataset) > 1:
        mid = int(len(dataset) / 2)
        if dataset[mid] == find_num:  # find it
            print("找到数字", dataset[mid])
        elif dataset[mid] > find_num:  # 找的数在mid左面
            print("\033[31;1m找的数在mid[%s]左面\033[0m" % dataset[mid])
            return binary_search(dataset[0:mid], find_num)
        else:  # 找的数在mid右面
            print("\033[32;1m找的数在mid[%s]右面\033[0m" % dataset[mid])
            return binary_search(dataset[mid + 1:], find_num)
    else:
        if dataset[0] == find_num:  # find it
            print("找到数字啦", dataset[0])
        else:
            print("没的分了,要找的数字[%s]不在列表里" % find_num)
binary_search(data, 66)

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
def calc (n):
    print(n)
    if int (n/2) >0:
        return calc(int(n/2))
    print("-->",n)
calc(10)

• 3.5 函数的高阶

变量可以指向函数，函数的参数能接收变量，那么一个函数就可以接收另一个函数作为参数，这种函数就称之为高阶函数。

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author:zhangyy
def add(x, y, f):
    return f(x) + f(y)
res = add(3, -6, abs)
print(res)