Python Learning Path 19-File IO

This blog will cover Python's file processing and related input and output, which will involve file objects (its built-in functions, built-in methods and properties), standard file and file system access methods, and file execution. (Welcome everyone to my new blog to take a walk)

File Object

The file object can be used not only to access normal disk files, but also to access "files" on any other type of abstraction. The built-in function open () returns a file object that is used for subsequent related operations of the file.

File built-in functions (open () and files ())

As a key, the built-in function open () and file () provide a common interface for initializing input/output (I/O) operations. The open () function returns a file file object when the file is successfully opened, and throws a IOError exception if unsuccessful. The syntax for the open () function is as follows:
file_object = open(file_name, access_mode="r", buffering=-1)
file_name is the file name of the file that will be opened, either a relative path or an absolute path. Access_mode is also a string that represents the open file mode, with "R" (for Read), "W" (For Write), "a" (for append). with "R" The file opened by the schema must be present. Open the file in "W" mode, if the file does not exist, it will be created, if the file already exists, then the file is emptied to write data. " A "mode is similar to" w ", the only difference is that" a "is adding data at the end of the file and does not empty the original data of the file. If the file does not exist, create it. Access_mode defaults to" R ". The buffering is used to indicate the buffering method used to access the file. Where 0 means no buffering, 1 means that only one row of data is buffered, and any other numeric value greater than 1 represents the buffer size using the given value. This parameter is not provided or a negative value is used to represent the system default buffering mechanism. See in more detail:

File built-in methods

After open () executes successfully and returns a file object, all subsequent operations on the file are carried out through this handle. There are 4 types of file methods: input, output, move within the file, and iterate.

Input

The read () method is used to read bytes directly into a string, reading a given number of bytes at most. The size parameter is not given (default is-1) or the size value is negative, and the file is read until the end.
The ReadLine () method reads a line of the file, and then the entire line (including the line terminator) is returned as a string. Similar to the Read () method, it also has an optional size parameter, which defaults to-1, which represents the end of the read line. If the parameter is provided, such as 5, it will read only 5 characters of that line
The ReadLines () method does not return a string like the other two methods. He would read all the lines (remaining) and then return them as a list of strings. Its optional parameter sizhint represents the maximum byte size returned. If it is greater than 0, Then all the rows returned should have sizeint bytes.

Output

Wirte () The function of the built-in method is the opposite of Read () and ReadLine (). It writes a string containing text data or binary data blocks to a file.
As with ReadLines (), the Writelines () method is a list-based operation that takes a list of strings as parameters and writes them to the file. But the line terminator does not automatically join, and if necessary, you must call the Writelines () money at the end of each line with a line terminator .

Moving within files

The Seek () method (similar to the fseek () function in C) can move the file pointer to a different location in the file. The offset byte represents the relative offset to a position. The default value for the position is 0, which means that from the beginning of the file (that is, the absolute offset), 1 represents the current position, 2 delegates are counted from the end of the file.
The Tell () method complements the Seek () method, which tells you where the current file pointer is located in the file – in bytes from the beginning of the file.

File iterations

File iterations are so easy for programmers to access files:

f = open("test.txt""r")forin f:    print eachLine

Other

Close () ends the access to it by closing the file.
The Fileno () method returns a descriptor for the open file. This is an integer
Calling the flush () method directly writes the data in the internal buffer to the file immediately, rather than passively waiting for the output buffer to be written.

It's time for a vote.

The above pull so much, or hands-on practice intuitive, to write some demo

>>> f = open ("Test","R") >>> Fileno (f) Traceback (most recent): File"<stdin>", line1,inch<module>nameerror:name' Fileno 'is not defined>>> F.fileno ()3>>> F.tell ()0>>> forEachlineinchF:...Print Eachline,...This file just forTest.line1Line2@line3!line4*end!!! >>> F.tell () $>>> F.seek (0,0) >>> F.tell ()0>>>

>>> f = open("newfile""w")>>> f.write("This is a test")>>> f.tell()14>>> f.writelines(["line1""line2""line3"])>>> f.close()>>> f = open("newfile""r"forin f:...     print eachLine,...

File built-in properties

File objects In addition to methods, there are some data properties. These properties hold additional data related to the file object.

properties of the file object	Description
File.closed	Represents a file to close
File.encodeing	The encoding used by the file
File.mode	Access mode when the file is opened
File.name	Filename
File.newline	To read to the line terminator is none, only one line terminator is a string, and when the file has multiple line separators, it is a list that contains all the currently encountered line Terminators

Standard file

Standard files have these 3: standard input, standard output, standard error
A handle to these files can be accessed through the SYS module in Python. Sys.stdin, sys.stdout, sys.error represent standard input, standard output, standard error, respectively. In general, the print statement is output to Sys.stdout, raw_ Input () is received from Sys.stdin.

Command-line arguments

I believe that the students familiar with C language are familiar with command line parameters, in C language, argc and argv respectively represent the number of parameters and parameter vectors. The argv variable represents an array of strings that consist of each parameter entered from a command line, and the ARGC variable represents the number of arguments entered. In Python, The ARGC is not there. The SYS.ARGV in Pyhton is quite the argv of C, and Len (SYS.ARGV) is the equivalent of ARGC in C. In short:
-SYS.ARGV is a list of command line arguments
-Len (SYS.ARGV) is the number of command line arguments

Look at a small example:

##argvTest.pyimport sysprint"you entered""arguments..."print"they were: ", str(sys.argv)

likai@likai:~/python$ 4344.445were:  [‘argvTest.py‘‘43‘‘test‘‘44.44‘‘haha‘]

File system

Access to file systems is mostly implemented through Python's OS modules. This module is the primary interface for Python to access the operating system functionality. The OS module is actually just the front end of the module that is actually loaded, and the specific implementation relies on the specific operating system.
The OS module can manage the process and process runtime environment, and the OS module is responsible for most of the file system operations. Of course, this blog is mainly about OS file system operation. These actions include deleting/renaming files, traversing the directory tree, and managing file permissions.
Another module, Os.path, can do some action on the pathname. It provides functions such as managing and manipulating various parts of the file path name, obtaining file or subdirectory information, file path queries, and so on.

File/directory Access functions for OS modules

function	Description
File processing
Mkfifo ()/mknod ()	Create a named pipe/create a file node
Remove ()/unlink ()	deleting files
Rename ()/renames ()	Renaming files
Stat ()	Return file information
Sysmlink ()	Creating Symbolic Links
Utime ()	Update Time stamp
Tmpfile ()	Create disease open (' w+b ') a new temporary file
Walk ()	Generate all file names under a directory tree
Directory/Folder
ChDir ()	Change the current working directory
Chroot ()	Change the root directory of the current process
GETCWD ()	Return to current working directory
mkdir ()/mkdirs ()	Create a directory/multi-level catalog
RmDir ()/rmdirs ()	Delete directory/multi-level directory
Access/Permissions
Access ()	Verify Permissions
chmod ()	Change permissions
Chown ()	Change owner
Umask ()	Set default Permissions
File descriptor Operations
Open ()	The underlying operating system open
Read ()/write ()	Read/write Data
DUP ()/DUP32 ()	Copy file descriptor/function same, but copy to another file descriptor
Device number
Makedev ()	Create an original device number from the major and minor device numbers
Major ()/minor ()	Get the Major/minor device number from the original device number

Path name access functions in the Os.path module

function	Description
Separated
BaseName ()	Remove directory path, return file name
DirName ()	Remove file name, return directory path
Join ()	Make separate parts a path name
Split ()	Returns (DirName (), basename ()) tuples
Splitdrive ()	Return (dirvename, pathname) tuples
Splitext ()	Return (filenameextension) tuples
Information
Getatime ()	Return last access time
Getctime ()	Return file creation time
Getmtime ()	Return file modification Time
GetSize ()	Return file size
Inquire
Exists ()	Specifies whether the path exists
Isabs ()	Specifies whether the path is an absolute path
Isdir ()	Specifies whether the path exists and is a directory
Isfile ()	Specifies whether the path exists and is a file
Islink ()	Specifies whether the path exists and is a symbolic link
Ismount ()	Specifies whether the path exists and is a mount point
Samefile ()	Two path names pointing to the same file

End

Finally end this blog with an example of Python core programming

#!/usr/bin/env PythonimportOS forTmpdirinch('/tmp ',' C:/windows/temp '):if OS. Path.isdir (Tmpdir): BreakElse:Print ' No temp directory available 'Tmpdir ="'ifTmpdirOS. ChDir (tmpdir) CWD =OS. GETCWD ()Print ' * * * Current temporary directory '    PrintCwdPrint ' * * * * Creating example Directory ... '    OS. mkdir (' Example ')OS. ChDir (' Example ') CWD =OS. GETCWD ()Print ' * * * New working directory: '    PrintCwdPrint ' * * * original directory listing: '    Print OS. Listdir (CWD)Print ' * * * * Creating test file ... 'File = Open (' Test ',' W ') File.write (' foo\n ') File.write (' bar\n ') File.close ()Print ' * * * updated directory listing: '    Print OS. Listdir (CWD)Print "* * * * renaming ' test ' to ' filetest.txt '"    OS. Rename (' Test ',' Filetest.txt ')Print ' * * * updated directory listing: '    Print OS. Listdir (CWD) path =OS. Path.join (CWD,OS. Listdir (CWD) [0])Print ' * * * full file pathname: '    PrintPathPrint ' * * * (pathname, basename) = = '    Print OS. Path.split (Path)Print ' * * * (filename, extension) = = '    Print OS. Path.splitext (OS. Path.basename (Path))Print ' * * * * displaying file contents: 'File = open (path) Alllines = File.readlines () file.close () forEachlineinchAlllines:PrintEachline,Print ' * * * deleting test file '    OS. Remove (Path)Print ' * * * updated directory listing: '    Print OS. Listdir (CWD)OS. ChDir (OS. Pardir)Print ' * * * deleting Test directory '    OS. RmDir (' Example ')Print ' * * * done '

Output Results (Linux)

Likai@likai-lenovo-g490:~/python$pythonospathex.py*** Current Temporary Directory/tmp*** Creating Example Directory ...*** New Working Directory:/tmp/example*** Original Directory listing:[]*** Creating testfile...*** Updated Directory listing:[' Test ']*** Renaming' Test 'To' Filetest.txt '*** Updated Directory listing:[' Filetest.txt ']*** Fullfilepathname:/tmp/example/filetest. txt*** (Pathname,basename) == ('/tmp/example ',' Filetest.txt ')*** (filename, extension) = = (' Filetest ','. txt ')*** DisplayingfileContents:foobar*** Deleting testfile*** Updated directory listing:[]*** Deleting Test directory*** Done

Python Learning Path 19-File IO