5. File Processing

Used to process file content in the system

Under what circumstances do I need to process files?§ Read the configuration file § read the data information § analyze and process the log file § Save the data to the file Open a file
Method 1:Open ('filename', ['Mode']) Method 2:File ('filename', ['Mode']) Mode:A: append W: Write and replace old one R: read, default mode B: binary files +: read/write mode (R +: Read and append. W +: read and write. A +: readable and appendable) For example:

>>> open(‘/root/file.txt‘)<open file ‘/root/file.txt‘, mode ‘r‘ at 0x7fa536269540>>>> open(‘/root/file.txt‘,‘w‘)<open file ‘/root/file.txt‘, mode ‘w‘ at 0x7fa5362694b0>>>> file(‘/root/file.txt‘,‘a‘)<open file ‘/root/file.txt‘, mode ‘a‘ at 0x7fa536269540>

Read a file (Readline, readlines ): Readline reads a file in one row until it is read; Readlines reads the end of the text from the current line.

1. >>> a=open(‘/root/file.txt‘)
2. >>> a.readline()
3. ‘1:root:x:0:0:root:/root:/bin/bash\n‘
4. >>> a.readline()
5. ‘2:bin:x:1:1:bin:/bin:/sbin/nologin\n‘
6. >>> a.readlines()
7. [‘3:daemon:x:2:2:daemon:/sbin:/sbin/nologin\n‘,‘4:adm:x:3:4:adm:/var/adm:/sbin/nologin\n‘,‘5:lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin\n‘]
8. >>> a.readline()
9. ‘‘

Write () Write a row>>> A = open ('/root/file.txt', 'A') >>>. write ('6: mysql: X: 4: 7: LP:/var/spool/lpd:/sbin/nologin \ n')>. close () truncate (n) file content is retained for only 2 Characters >>> A = open ('/root/file.txt', 'A') >>>. truncate (2) >>>. close () Seek (n) the cursor returns to the nth character at the beginning of the file. For example, seek (0) returns to the beginning.>>> A. Seek (0) >>> A. Readline () 'root: X: 0: 0: Root:/root:/bin/bash \ N' Exercise: print a complete file

1. #!/usr/bin/pythonfile=open(‘/root/file.txt‘,‘r‘)whileTrue:        line = file.readline()        if len(line)==0:break        print line,

Exercise: print files and use split (':') to implement functions similar to awk:

1. #!/usr/bin/pythonfile=open(‘/root/file.txt‘,‘r‘)whileTrue:        line = file.readline()        if len(line)==0:break        newline = line.split(‘:‘)        print newline[0],‘--‘,newline[1][[email protected] python_scripts]# python 8file.py root -- xbin -- xdaemon -- xadm -- xlp -- x

Exercises: Employee information is stored in the file emp.info. Read the file, list the employee IDs in the file, and output the employee details based on the employee ID.

1. [[email protected] python_scripts]# cat emp.info01      lk      18610314061     it02      tom     13539393939     net03      jack    15093949348     mark04      james   13892387464     sale

1. #!/usr/bin/pythonfile=open(‘/root/python_scripts/emp.info‘,‘r‘)emp_ids=[]whileTrue:        line=file.readline()        if len(line)==0:break        line=line.split()        emp_ids.append(line[0])print emp_idswhileTrue:        id = raw_input(‘input [id] to show info:‘)        file.seek(0)        whileTrue:                line=file.readline()                if len(line)==0:                        print ‘We dont have id ‘,id                        break                 if id == line.split()[0]:                        print line                        file.seek(0)                        id = raw_input(‘input [id] to show info:‘)

5. File Processing