Read and write operations for python--files

Python provides the necessary functions and methods for basic file operation by default

How to open the file:

Open (Name[,mode[buf]]) Name: File path mode: Open mode buf: buffer buffering size

File read mode:

Read ([size]): Read file (read size byte, read all by default)

ReadLine ([size]): reads a row

ReadLine ([size]): Read buffer buf (IO. Default_set_buffer), returns the list of each row

ITER: Using an iterator to traverse the Read file F.open (name); iter_f = iter (f); Using the for line in Iter_f Loop iterator

With open (' pi_digits.txt ') as F: # Default mode is ' R ', read-only mode

Contents = F.read () # reads the entire contents of the file

File Write Method:

Write (str): Writes a string to a file

Writelines (sequence_of_strings): Writes multiple lines to a file, with arguments as objects that can be iterated

When write (str) is called, the Python interpreter calls the system call to write the contents to disk, but the Linux kernel has a file caching mechanism, so caches the kernel buffers, and when close () or flush () is called, the content is actually written to the file

or write -in data volume greater than or equal to write cache, write cache will also be synchronized to disk

Purpose of closing the file

1: Write cache sync to disk

The number of open files per process in the 2:linux system is limited

3: If the number of open files to the system limit, the open file will fail

Python file pointer operation:

Seek (Offset[,whence]) move the file pointer

Offset: Offsets, can be a negative number

Whence: Offset relative position

How the Python file pointer is positioned:

Os. Seek_set start position relative to the file 0

Os. Seek_cur relative to the current position of the file 1

Os. Seek_end position relative to end of file 2

Python file properties:

File.fileno (): File descriptor;

File.mode: File open permission;

File.encoding: File encoding method;

File.closed: Whether the file is closed;

Python Standard Files:

Standard input file: Sys.stdin; Read-only descriptor is 0

Standard output file: sys.stdout; Write-only descriptor is 1

Standard error file: Sys.stderr; Write-only descriptor is 2

Python command-line arguments:

The SYS module provides the SYS.ARGV property, which allows you to get command-line arguments. SYS.ARGV is a string sequence that holds the command-line arguments, where sys.argv[0] is the file name and 1~n is the true argument

Python File Encoding method

The default encoding format for Python files is ASCII format, to be written in Chinese you can convert the encoding format

1. A = Unicode.encode (U ' hello ', ' utf-8 ') conversion, a Chinese character occupies 3 bytes in ASCII code and 2 bytes in Unicode.

2. Create a file in utf-8 format directly. Create the specified encoding format file using the methods provided by the codecs module:

Codecs.open (fname, mode, encoding, errors, buffering): Open a file using the specified encoding format

3. You can also create a file in the specified encoding format using the system-provided open () function:

Open (file, mode= ' R ', Buffering=-1, Encoding=none, Errors=none, Newline=none, Closefd=true, Opener=none)

Simple Linux File system

Here is the process for Python action files

  .python  file access 1. In Python to access the file, the first to open the file, that is, openr:  read-only w:  write only, the file already exists is emptied, does not exist create a: Append, write to the end of the file. If the file exists, go to chase     add at the end of the file. File does not exist to create    +-: update (Readable writable)  r+: Open in read/write mode w+: Open in read/write mode (see W) A + : Open in read-write mode (see a) RB: Open WB in binary read mode: Open in binary write mode ab: Open in binary append mode (see a) rb+: Open in binary read/write mode (see r+) wb+: Open in binary read-write mode (see w+) ab+: Open in binary read/write mode (see A +)  2. Open the file. Open opening file read reading file, close file  import codecsfd = Codecs.open (' 2.txt ') print Fd.read () fd.close ()  >>> 11111222233333aaaaabbbbbcccccc 3. What are the methods of viewing a file  import CODECSFD = Codecs.open (' b.txt ') print fd.read () print dir (FD) Fd.close ()  >>> 111112222333333[' close ', ' Closed ', ' encoding ', ' errors ', ' Fileno ', ' flush ', ' isatty ' , ' mode ', ' name ', ' newlines ', ' next ', ' read ', ' Readinto ', ' readline ', ' readlines ', ' seek ', ' softspace ', ' Tell ', ' truncate ' , ' write ', ' writelines ', ' Xreadlines '] 1>fd.read () method, the Read () method reads the entire document. &NBSP;FD = Codecs.open (' 2.txt ') Text = Fd.read () print type (text)  >>><type ' str ' &GT;&NBSP;&NThe Bsp;2>replace () function replaces an element in the file. Opens the file, reads it, and then operates on the entire string. Replace 1 in 2.txt file with Z&NBSP;FD = Codecs.open (' 2.txt ') a1 = Fd.read () Print a1a2 = A1.replace (' 1 ', ' Z ') print A2 >>> 11111222233333aaaaabbbbbcccccc zzzzz222233333aaaaabbbbbcccccc 3> Write files, Codecs.open () function, avoid file garbled  fd = Codecs.open (' 3.txt ', ' W ') fd.write (' liuzhenchuan\n ') fd.write (' Hello world\n ') Fd.write (' xiaban\n ') fd.close ()  >>> Liuzhenchuanhello worldxiaban  4>fd.readlines () method, Read the file, and finally put the contents of each line of the file as a string in a list &NBSP;FD = open (' 3.txt ') print fd.readlines () fd.close ()  >>> [' liuzhenchuan\n ', ' Hello world\n ', ' xiaban\n ']  5>fd.readline () method, read file, read file line, type string >>> l   6> #fd. ReadLine () method, reads the file line, returns a string .          # Fd.next () method, reads the next line of the file, returns a string  fd = Codecs.open (' 3.txt ', ' R ') print Fd.readline () print fd.next () fd.close ()   >>> liuzhenchuan     Hello world  7> #write () method, mustMust pass in a string.  fd = Codecs.open (' 5.txt ', ' w+ ') fd.write (' a\nb\nc\n ') fd.close ()  >>> a     b    c   #writelines () method, must pass in a list/sequence FD = Codecs.open (' 6.txt ', ' W ') fd.writelines ([' 123\n ', ' 234\n ', ' 345\n ']) fd.close ()  >>> 123    234    345  8 >with usage, do not need to use Fd.close () to close the file with Codecs.open (' 3.txt ', ' RB ') as fd:    print fd.read ()      Fd.close ()  >>> liuzhenchuanhello worldxiaban  9> Print file line number and file contents with Codecs.open (' 2. TXT ') as fd:    for Line,value in Enumerate (FD):        print line, value, >>> 0 liuzhenchuan    1 Hello world    2 xiaban  10> Filter the contents of a file line with Codecs.open (' 3.txt ') as fd:    for Line,value in Enumerate (FD):     & nbsp;   if line = = 3-2:            Print value >>> Hello world  11> import the Linecache module, using the Linecache.getline () method, Get the contents of a fixed line of files import linecachecount = Linecache.getline (' 3.txt ', 1) print count >>> Liuzhenchuan

Read and write operations for python--files