Python File System Function: os Module

1. Classification of OS Module Method

(1) Catalogue:

    chdir() changes the working directory
    chroot() sets the root directory of the current process
    listdir() lists all file names in the specified directory
    mkdir() Creates the specified directory
    makedirs() Create multilevel directories
    getcwd() returns to the current working directory
    rmdir() Deletes the specified directory
    removedirs() deletes multilevel directories

(2) Documents:

    mkinfo() creates pipes
    mknod() Creates device files
    remove() delete files
    unlink() deletes linked files
    rename() rename
    stat() returns file status information
    symlink() creates symbolic links
    utime() update timestamp
    tmpfile() creates and opens (w+b) a new temporary file

(3) Access privileges

    access(path, mode) determines whether a specified user has access to os. access ('/tmp', 0) uid of 0 and whether a user has access to the / tmp directory
    chmod(path,mode) modifies the permission os.chmod('/tmp/s',0640) to change the permission / tmp/s to 640
    chown(path,uid,gid) modifies ownership and group  
    umask() sets the default permission mode os.umask(022)
    

(4) Equipment documents

    makedev() create device
    major() Specifies the device to get the master device number
    minor() specifies the device to get the secondary device number
    

(5) File descriptors

    open() Lower IO Open
    read() Lower IO reading
    write() Lower IO write

4 and 5 are relatively less used
 Supplement:
    os.walk() is equivalent to the tree command
    >>> import os
    >>> a1 = os.walk('/root')
    >>> a1.next()
    ('/root',
     ['.subversion', '.ssh', '.ipython', '.pki', '.cache'],
     ['test.py',
      '.bash_history',
      '.cshrc',
      '.bash_logout',
      '.tcshrc',
      '.bash_profile',
      '.mysql_history',
      '.bashrc',
      '.viminfo'])
    Returns a tuple consisting of (file name, [folder], [file])
    

2. path module in OS module

1) Related to file path

    basename()      Path base name
    dirname()       Path directory name
    join()          Consolidate filenames
    split()         Return dirname(),basename()tuple
    splitext()      Return(filename,extension)tuple
    
    //Example:
    >>> dir1 = os.path.dirname('/etc/sysconfig/iptables-config')
    >>> dir1
    '/etc/sysconfig'
    >>> file1 = os.path.basename('/etc/sysconfig/iptables-config')
    >>> file1
    'iptables-config'
    >>> os.path.join(dir1,file1)
     '/etc/sysconfig/iptables-config'
    >>> for filename in os.listdir('/tmp'):
            print os.path.join('/tmp',filename)

2) Information

    getatime() returns the last access time to the file
    getmtime() returns the last modification time of the file
    getctime() returns the last time the file was changed
    getsize() returns the size of the file

3) Query

    exists()        Determine whether the specified file exists    isabs()         Determine whether the specified path is an absolute path
    isdir()         Is it a directory?
    isfile()        Is it a document?
    islink()        Whether symbolic links exist or not
    ismount()       Is it a mount point?
    sanefile(f1,f2) Does the two paths point to the same file?
    
    //Example: To judge whether a file exists or not, open it, let the user input multiple lines of data repeatedly through the keyboard, and save it to this file.
    >>> import os 
    >>> import os.path
    >>> if os.path.isfile('/tmp/s'):
            f1 = open('/tmp/s','a+')
        while True:
            a2 = raw_input("Input >> ")
            if a2 == 'q' or a2 == 'quit' :
                break
            f1.write(a2+'\n')
        f1.close()
        

4) Object persistent storage

    The process of changing variables from memory to storage or transmission is called serialization.
    pickle,marshal,DBM Interface, shelve Modular
    
    pickle   Persistent storage of memory objects in files
    >>> import pickle
    >>> dict1 = {'x':1,'y':2,'z':'hello world'}
    >>> f1 = open('/tmp/s','a+')
    >>> pickle.dump(dict1,f1)           Keep dictionaries in files by passing
    >>> f1.close()
    # file /tmp/s
    /tmp/s: ASCII text
    # cat /tmp/s
    (dp0
    S'y'
    p1
    I2
    sS'x'
    p2
    I1
    sS'z'
    p3
    S'hello world'
    p4
    s.
    >>> f2 = open('/tmp/s','a+')
    >>> dict2 = pickle.load(f2)         Reloading
    >>> dict2
    {'x':1,'y':2,'z':'hello world'}