Python Standard Library

The os Module

The os module provides a unified interface to many operating system functions.

Most of the functions in this module are implemented by platform-specific modules, such as posix or nt. The os module automatically loads the right implementation module when it is first imported.

Working with Files

The built-in open function lets you create, open, and modify files, as shown in Example 1-27. This module adds those extra functions you need to rename and remove files.

Example 1-27. Using the os Module to Rename and Remove Files

File: os-example-3.py

import os
import string

def replace(file, search_for, replace_with):
    # replace strings in a text file

    back = os.path.splitext(file)[0] + ".bak"
    temp = os.path.splitext(file)[0] + ".tmp"

    try:
        # remove old temp file, if any
        os.remove(temp)
    except os.error:
        pass

    fi = open(file)
    fo = open(temp, "w")

    for s in fi.readlines():
        fo.write(string.replace(s, search_for, replace_with))

    fi.close()
    fo.close()

    try:
        # remove old backup file, if any
        os.remove(back)
    except os.error:
        pass

    # rename original to backup...
    os.rename(file, back)

    # ...and temporary to original
    os.rename(temp, file)

#
# try it out!

file = "samples/sample.txt"

replace(file, "hello", "tjena")
replace(file, "tjena", "hello")

Working with Directories

The os module also contains many functions that work on entire directories.

The listdir function returns a list of all filenames in a given directory, as shown in Example 1-28. The current and parent directory markers used ...