Python攻克之路-文件操作

文件操作
一.文件操作的流程
1. 建立文件
2. 建立文件对象,就是打开文件open函数,即打开文件句柄
3.模式操作,如读r,写w
4.调用方法,如read()
5.关闭文件(.close把缓冲区的数据写入到磁盘,即使不手动做,python也会自动执行,前提是程序执行完,但是建议每次都手动加上)
注意：能调用方法的一定是对象,文件也是对象

In [6]: l1=[1,2,3] #对象
In [7]: l1.append('4') #调用的方法
In [8]: l1
Out[8]: [1, 2, 3, '4']

二.文件操作的模式
注：读模式只能读,写模式只能写

[root@zabbix day8]# cat file.txt
hello reid

1.读r：

In [15]: f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
In [16]: data=f.read(5) ##5显示多少个字符,在Py3中文和英文一样,默认是取所有
In [17]: print(data)
hello

2.写w：先把之前的清空,再写

[root@zabbix day8]# cat file-operate.py
#!/usr/local/python3/bin/python3
f=open('/root/py/fullstack_s2/week2/day8/file.txt','w')      ##对象创建时,就已经把文件内容清空,文件不存在就会创建文件
data=f.write('hello world')
print(data)
f.close()
[root@zabbix day8]# python3 file-operate.py
11
[root@zabbix day8]# cat file.txt
hello world[root@zabbix day8]###连续写不换行
[root@zabbix day8]# cat file-operate.py
#!/usr/local/python3/bin/python3
f=open('/root/py/fullstack_s2/week2/day8/file1.txt','w')
f.write('hello world')
f.write('tom')
f.close()
[root@zabbix day8]# python3 file-operate.py
[root@zabbix day8]# cat file1.txt
hello worldtom[root@zabbix day8]#

分析：文件在内存里,如划分成一行行的,每行里还划分成一个个格,如存一个hello,一个个单位的存储,存完后,如果后面还有存储它就会接着存,不会有任何东西,如果需要空格可以在里面加空格,然后空格就占用一个位置,可以加换行符,如果不加就会走到行的最大量才换.实际上python有一个指针,如在写文件时,都在开始处,如写hell,指针一开始在h,写到l时就停在l,再写其他就从l开始写

f.write('hello world \n')
f.write('tom')

3.追加a：在光标所在处开始追加

[root@zabbix day8]# cat file-operate.py
#!/usr/local/python3/bin/python3
f=open('/root/py/fullstack_s2/week2/day8/file1.txt','a') ##a追加
f.write('\n hello world \n')
f.write('tom')
f.close()[root@zabbix day8]# cat file1.txt
hello worldtom[root@zabbix day8]# [root@zabbix day8]# python3 file-operate.py
[root@zabbix day8]# cat file1.txt
hello worldtom
hello world

4. r+ 读写,光标默认在起始位置,常用的模式***

[root@zabbix day8]# cat file1.txt
hi reid
hello world
In [30]: f=open('/root/py/fullstack_s2/week2/day8/file1.txt','r+')
In [31]: print(f.readline())
hi reid
In [32]: f.write('tom')
Out[32]: 3
[root@zabbix day8]# cat file1.txt
hi reid
hello world
tom[root@zabbix day8]#

5. w+ 写读

[root@zabbix day8]# cat file1.txt
hi reid
hello world
In [34]: f=open('/root/py/fullstack_s2/week2/day8/file1.txt','w+') ##打开后,就直接格式化之前的内容
In [35]: print(f.readline()) ##直接读时为空
In [36]: f.write('tom') ##写入新内容
Out[36]: 3
In [37]: print(f.tell()) ##写入新内容后光标所在3,再读也是空
3
In [38]: print(f.readline())
In [39]: f.close()
[root@zabbix day8]# cat file1.txt
tom[root@zabbix day8]#

把光标重新移动：

[root@zabbix day8]# cat file1.txt
tom
In [41]: f=open('/root/py/fullstack_s2/week2/day8/file1.txt','w+')
In [42]: f.write('reid \n')
Out[42]: 6
In [43]: print(f.readline())
In [44]: f.seek(0)
Out[44]: 0
In [45]: print(f.readline())
reid
In [46]: f.close()

6. a+ 追加可读,光标默认是在最后

[root@zabbix day8]# cat file1.txt
reid
In [47]: f=open('/root/py/fullstack_s2/week2/day8/file1.txt','a+')
In [48]: print(f.tell())
6
In [49]: print(f.readline())

三.文件操作具体方法

1.readline按行读

[root@zabbix day8]# cat file-operate.py
#!/usr/local/python3/bin/python3
f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
print(f.readline())
print(f.readline())
f.close()[root@zabbix day8]# python3 file-operate.py
I heard the echo, from the valleys and the heartOpen to the lonely soul of sickle harvesting

2.read按字符读

[root@zabbix day8]# cat file-operate.py
#!/usr/local/python3/bin/python3
f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
print(f.read(5))
print(f.read(5))
f.close()
[root@zabbix day8]# python3 file-operate.py
I hea 读到5个字符时,还有一个换行符
rd th

3.readlines输出列表

In [1]: f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
In [2]: print(f.readlines())
['I heard the echo, from the valleys and the heart\n', 'Open to the lonely soul of sickle harvesting\n', 'Repeat outrightly, but also repeat the well-being of\n', 'Eventually swaying in the desert oasis\n']

4.使用for循环使用readlines直接读列表里的内容

In [3]: f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
In [4]: for i in f.readlines():
...: print(i)
...:
I heard the echo, from the valleys and the heart       ##打印时本身就有一个换行,再加print默认有个换行Open to the lonely soul of sickle harvestingRepeat outrightly, but also repeat the well-being ofEventually swaying in the desert oasis

strip()把末尾的换行自动去掉

In [7]: f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
In [8]: for i in f.readlines():
...: print(i.strip())
...:
I heard the echo, from the valleys and the heart
Open to the lonely soul of sickle harvesting
Repeat outrightly, but also repeat the well-being of
Eventually swaying in the desert oasis

5.实现处理文件中某一行,增加一个字符串

#!/usr/local/python3/bin/python3
num=0
f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
for i in f.readlines():num +=1             ##每读一行就加1if num == 2:        ##读到第2行时就加上需要加的字符串print(i.strip(),'======reid') else:print(i.strip())
f.close()
[root@zabbix day8]# python3 file-operate.py
I heard the echo, from the valleys and the heart
Open to the lonely soul of sickle harvesting ======reid
Repeat outrightly, but also repeat the well-being of
Eventually swaying in the desert oasis

优化一：

[root@zabbix day8]# cat file-operate.py
#!/usr/local/python3/bin/python3
num=0
f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
for i in f.readlines():num +=1if num == 2:i='+++++'.join((i.strip(),'reid'))   ##直接使用i=,节省了一个Print，字符串拼接时使用joinprint(i.strip())
f.close()
[root@zabbix day8]# python3 file-operate.py
I heard the echo, from the valleys and the heart
Open to the lonely soul of sickle harvesting+++++reid
Repeat outrightly, but also repeat the well-being of
Eventually swaying in the desert oasis

优化二:

[root@zabbix day8]# cat file-operate.py
#!/usr/local/python3/bin/python3
f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
data=f.readlines()
#只把文件读了一下,把内容取出来,马上就关闭,剩下就自己处理,使用文件的时间短,优化一是整个操作都在文件打开过程中,看实际,如果频繁操作效率不高
f.close
num=0
for i in data:num +=1if num == 2:i='+++++'.join((i.strip(),'reid'))print(i.strip())
f.close()
[root@zabbix day8]# python3 file-operate.py
I heard the echo, from the valleys and the heart
Open to the lonely soul of sickle harvesting+++++reid
Repeat outrightly, but also repeat the well-being of
Eventually swaying in the desert oasis##不使用定义变量：num,使用enumerate来接收两个变量
[root@zabbix day8]# cat file-operate.py
#!/usr/local/python3/bin/python3
f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
for i,v in enumerate(f.readlines()):if i == 2:v='   ******'.join((v.strip(),'reid'))print(v.strip())
f.close()
[root@zabbix day8]# python3 file-operate.py
I heard the echo, from the valleys and the heart
Open to the lonely soul of sickle harvesting
Repeat outrightly, but also repeat the well-being of   ******reid
Eventually swaying in the desert oasis

优化三：使用列表直接修改

In [9]: f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
In [10]: data=f.readlines()
In [11]: data[1]='Open to the lonely soul of sickle harvesting ppppppppppp'
In [12]: print(data)
['I heard the echo, from the valleys and the heart\n', 'Open to the lonely soul of sickle harvesting ppppppppppp', 'Repeat outrightly, but also repeat the well-being of\n', 'Eventually swaying in the desert oasis\n']

优化四：对readlines的优化方式：**** 推荐用法
注：readlines是把数据都读到内存里,如果文件大的话一下子就会崩溃

In [1]: f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
In [2]: for i in f: #文件本身在磁盘上,for i in f时没有对磁盘作任何操作...:     print(i.strip()) ##内部,python会对for做了特殊处理,把f做成迭代器,它会用时取一个,不用就不取,对于文件本用一行取一行,数据在磁盘,使用时在内存,使用算法计算实现...:
I heard the echo, from the valleys and the heart
Open to the lonely soul of sickle harvesting
Repeat outrightly, but also repeat the well-being of
Eventually swaying in the desert oasi

对某行处理：

[root@zabbix day8]# cat file-operate.py
#!/usr/local/python3/bin/python3
f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
num=0
for i in f:num +=1if num == 2:i='+++++'.join((i.strip(),'reid'))print(i.strip())
f.close()
[root@zabbix day8]# python3 file-operate.py
I heard the echo, from the valleys and the heart
Open to the lonely soul of sickle harvesting+++++reid
Repeat outrightly, but also repeat the well-being of
Eventually swaying in the desert oasis

summary: readlines与迭代器对比
readlines: 有一个文件,内容一行行在磁盘里存储着,使用readlines是完全把整个文件copy到内存里,对它进行操作,如果文件的太大就会影响性能
迭代器的实现：做一个迭代器在内存里,当使用第一行内容时,就取第一行的内容,取到放在内容后,可以对它进行应用,如print下,print完后,内存就没有相当于del,是解释器做的,再到下一行,整个处理的过程中只有一行的内容

6.tell: 用于检测当前光标的位置

In [1]: f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
In [2]: print(f.tell()) #开始是0
0
In [3]: print(f.read(10))
I heard th
#光标所在的位置,包括空格,在python3里,字符集为utf-8时,英文是1个字母1个字符,一个中文占3个字符,python2是中英一样
In [4]: print(f.tell())
10

7.seek调整光标 ****
使用场景：服务器客户端上传下载,如上传100M的文件,传到50M时断了,使用断点续传时,如果判断到它传了50M,可以使用seek调整到50M的位置

In [5]: f=open('/root/py/fullstack_s2/week2/day8/file.txt','r')
In [6]: print(f.tell())
0
In [7]: print(f.read(2))
I
In [8]: print(f.tell())
2
In [9]: f.seek(0)
Out[9]: 0
In [10]: print(f.tell())
0

8.文件操作之flush
场景分析：当f.write时是没有写到disk,直到f.close后才写到disk,是先写到缓存中,直到满了或者close,如果实时写到disk会影响性能,不过在数据安全性高的场景就需要实时写磁盘,使用flush方法来实现,当write一条数据后,使用flush就会把缓存更新,把数据存放到磁盘上去

In [3]: f=open('test','w')
In [4]: f.write('reid is good')
Out[4]: 12
In [5]: f.write('hello')
Out[5]: 5
[root@zabbix day8]# cat test ##write后并没有写到disk
[root@zabbix day8]#
In [6]: f.flush() ##flush后把缓存的数据写到磁盘上
[root@zabbix day8]# cat test
reid is goodhello[root@zabbix day8]#

flush在进度条的使用

In [7]: import sys,time
In [8]: for i in range(30):
...: sys.stdout.write("*") #sys.stdout终端的输出
...: time.sleep(0.2)
****************************** ##这种情况,它是先写到缓存里,当30个完成写完,0.2*30=6秒钟后才统一显示实现进度条：
In [9]: for i in range(30):
...: sys.stdout.write("*")
...: sys.stdout.flush() ##加上flush后,就会每0.4秒打印一个*显示在终端
...: time.sleep(0.4)
...:
******************************另一种方法：
In [13]: for i in range(30):
...: print('*',end='',flush=True) #end等于空不换行,flush作为print的参数立刻刷新
...: time.sleep(0.1)
******************************

9.truncate():截断,取决于光标所在的位置开始截取
追加的情况：

[root@zabbix day8]# cat file1.txt
hello world
In [22]: f=open('/root/py/fullstack_s2/week2/day8/file1.txt','a')
In [23]: f.truncate(4)
Out[23]: 4
[root@zabbix day8]# cat file1.txt
hell[root@zabbix day8]#

写的情况：

[root@zabbix day8]# cat file1.txt
hello world
In [24]: f=open('/root/py/fullstack_s2/week2/day8/file1.txt','w')
In [25]: f.truncate(4)
Out[25]: 4
[root@zabbix day8]# cat file1.txt
[root@zabbix day8]#
In [26]: f.write('hi reid') ##先写再截取
Out[26]: 7
In [27]: f.truncate(4)
Out[27]: 4
[root@zabbix day8]# cat file1.txt
hi r[root@zabbix day8]#

10.with方法
在退出with语句后,会自动把文件进行关闭,不使用f.close()

In [153]: with open('file1.txt','r') as f:
...: print(f.readline())
...:
I heard the echo

在python2.7后,with可以同时对两个不同的对象操作

In [154]: with open('file1.txt','r') as f_read, open('file2.txt','w') as f_write:
...: for line in f_read:
...: f_write.write(line) ##读file1.txt文件,把每行写入file2.txt中

四.修改文件的思路(*****)
注：r与w的光标是不一致的,r是从起始开始,w写是从最后开始写的
思路一：直接在光标所在的位置修改

[root@zabbix day8]# cat file1.txt
I heard the echo
Open to the lonely
Repeat outrightly
Eventually swaying
In [66]: f=open('/root/py/fullstack_s2/week2/day8/file1.txt','r+')
In [67]: num=0
In [68]: for line in f:
...: num+=1
...: if num==3: ###按理论当num==3时,是光标所在行,当时在最后写
...: f.write(' ++++reid')
...: f.close()
[root@zabbix day8]# cat file1.txt
I heard the echo
Open to the lonely
Repeat outrightly
Eventually swaying
++++reid[root@zabbix day8]#[root@zabbix day8]# cat file1.txt
I heard the echo
Open to the lonely
Repeat outrightly
Eventually swaying
In [69]: f=open('/root/py/fullstack_s2/week2/day8/file1.txt','r+')
In [70]: num=0
In [71]: for line in f:
...: num+=1
...: if num==1: ##当num==1时,还是在最后一行写
...: f.write(' ++++reid')
...: f.close()
[root@zabbix day8]# cat file1.txt
I heard the echo
Open to the lonely
Repeat outrightly
Eventually swaying
++++reid[root@zabbix day8]#

思路二：创建新的文件,把旧文件每个读到一个新文件里,读到某一处理的行时,再处理,新的文件就修改完
注意：
a. 调用read,write的方法时,要是对象,如file文件,字符串不行
b. 创建一个新对象时,不要放进for循环中,否则会产生多个对象

[root@zabbix day8]# cat file1.txt
I heard the echo
Open to the lonely
Repeat outrightly
Eventually swaying[root@zabbix day8]# cat test.py
#!/usr/local/python3/bin/python3
f=open('/root/py/fullstack_s2/week2/day8/file1.txt','r')         ##从一个文件里读
f1=open('/root/py/fullstack_s2/week2/day8/file2.txt','w')        ##写入一个新创建的文件
num=0
for line in f:num+=1if num==3:                                                   ##当光标到第三行时操作#line='hello reid \n'    line=' '.join([line.strip(),'hello reid \n'])    f1.write(line)
f.close()
f1.close()[root@zabbix day8]# python3 test.py
[root@zabbix day8]# cat file2.txt
I heard the echo
Open to the lonely
Repeat outrightly hello reid  ###
Eventually swaying

转载于:https://www.cnblogs.com/reid21/articles/8506712.html

Python攻克之路-文件操作相关推荐

Python中的File(文件)操作
Python中的File(文件)操作针对磁盘中的文件的读写.文件I/O I 输入(input) O输出(Output) 文件操作步骤:1.打开文件 2.读写文件 3.关闭文件写入文件的操作:(把大 ...
详解Python中的File(文件)操作
目录 Python中的File(文件)操作写入文件的操作: 读取文件的操作: 一.文件操作相关函数 1. open() 打开文件 2. seek() 设置文件指针的位置 3. write() 写入内 ...
Python之路----文件操作
文件操作 1.能调用方法的一定是对象,比如数值.字符串.列表.元组.字典,甚至文件也是对象,Python中一切皆为对象. 1 str1 = 'hello' 2 str2 = 'world' 3 str ...
【八】Python全栈之路--文件操作
文章目录 1. 字典的相关函数 2. 集合的操作_函数 3. 文件基本操作 4. 文件扩展模式 1. 字典的相关函数字典的相关函数 # ### 字典的相关函数 dic = {} # 增 # 1.普通 ...
第三章：Python基础の函数和文件操作实战
本課主題 Set 集合和操作实战函数介紹和操作实战参数的深入介绍和操作实战 format 函数操作实战 lambda 表达式介绍文件操作函数介紹和操作实战本周作业 Set 集合和操作实战 Se ...
Python 开发-2 （文件操作，正则表达式，类，JSON，装饰器，异常处理，Socket）
文章目录文件操作递归创建目录删除文件或目录拷贝文件修改文件名或目录名文件路径名操作判断文件,目录是否存在文件大小与修改时间当前目录与目录切换遍历目录文件遍历目录下指定后缀目录文 ...
python处理二进制文件_python文件操作之二进制
列表项三元运算符号: a=3 b=7 val=a if a>b else val=b print(val) 文件处理首先给你一个文件,或者自己建立一个文件,那如何查看文件的内容呢? 1.安装 ...
python codecs.open()及文件操作-文本处理 with open
20210810 以二进制并追加的形式写入文件 20210731 f.write('\n') 换行写入 20210625 https://blog.csdn.net/a543402496/articl ...
Python基本语法_文件操作_读写函数详解
目录目录软件环境 file文件对象 open文件操作读文件 read读取所有文件内容 readline获取一行内容 readlines读取所有文件内容 readreadlinereadlines ...
【python教程】IO文件操作的常见用法
首先创建一个文件操作对象: f = open(file, mode, encoding) file指定文件的路径,可以是绝对路径,也可以是相对路径文件的常见mode: mode = "r& ...

Python攻克之路-文件操作

Python攻克之路-文件操作相关推荐

最新文章

热门文章