List current directory

Given a path to a directory the call to os.listdir(path) will return the names of the files, directories, symbolic links, etc. in that directory. In the simple case we can go over the elements using a for in loop and print out each one of them:

examples/python/ls_plain.py

#!/usr/bin/env python
from __future__ import print_function
import os

path = '.'

files = os.listdir(path)
for name in files:
    print(name)

In order to make the code Python 3 compatible I added from __future__ import print_function. The path is hard-code . indicating the current directory.

Otherwise the code seems to be straight forward.

List any directory

In order to make the script more flexible, let's accept an optional(!) directory name on the command line.

examples/python/ls_argv.py

#!/usr/bin/env python
from __future__ import print_function
import os,sys

path = '.'

if len(sys.argv) == 2:
    path = sys.argv[1]


files = os.listdir(path)
for name in files:
    print(name)

For this we also loaded the sys module and looked at the sys.argv. This array contains the list of things on the command-line excluding the python executable. So the first element (index 0) of this array is the name of the script, and if the user runs the script with a value on the command line then the length of the array will be 2 or more.

In this code we have path = '.' being the default value of path, but if there are two items on the command line, the script and presumably the path to another directory, then we replace the default value by the value provided on the command line.

The rest of the code is the same.

Check the inode for further details

In order to provide more information in the directory listing we have to check the inode table of the file. For this we need the path to the file which the the content of the path variable and the name of the file together. We use the os.path.join method that can join together two or more pieces of a directory path with the appropriate(!) connecting character. On Unix/Linux systems this will be a slash /, on MS Windows this will be a back-slash \ and on other operating systems it might be something else.

    full_path = os.path.join(path, name)
    print(full_path);

Then we call the os.stat method with the full path. It returns an object representing the content of the inode table of the give file or directory. This contains all the information about ownership of the file, right various groups have on the file, timestamps and a few more things.

The st_size method of this object returns the size of the file in bytes.

The inode.st_mode returns a number representing the rights on this file and the type of this file. we can use bitwise operations with the appropriate values to know which bit is set. I wrote a lot more about this in the article about stat in Node.js.

In these two line we check if the given thing is a file or a directory. (We have not dealt with symbolic links or other things that might be in the filesystem.

    print('  ' + ('f' if inode.st_mode & 0100000 else '-' ))
    print('  ' + ('d' if inode.st_mode & 0040000 else '-' ))

In case you are not familiar with this syntax the A if COND else B is the ternary operator of Python.

The alternative, and probably much more readable way is to call the os.path.isdir and os.path.isfile for the appropriate boolean (True or False) value, and to call the os.path.getsize method to fetch the size of the file.

The full script can be seen here:

examples/python/ls.py

#!/usr/bin/env python
from __future__ import print_function
import os,sys

path = '.'

if len(sys.argv) == 2:
    path = sys.argv[1]

files = os.listdir(path)
for name in files:
    print(name)

    full_path = os.path.join(path, name)
    print(full_path)

    inode = os.stat(full_path)
    print('  ' + str(inode.st_size))
    print('  ' + str(inode.st_mode))
    print('  ' + ('f' if inode.st_mode & 0100000 else '-' ))
    print('  ' + ('d' if inode.st_mode & 0040000 else '-' ))

    if os.path.isdir(full_path):
        print('    dir')
    elif os.path.isfile(full_path):
        print('    file')
    print('    ' + str(os.path.getsize(full_path)))