How to check whether a file exists?¶

The os module provides an easy way to interact with files, directories and other parts of your operating system. It contains many functions to list, change, copy, remove and examine files and directories.

import os

print(os.path.exists('README.rst'))

How to copy or remove a file?¶

os does these as well:

import os

os.system('python -c "print(6*7)"')

os.remove('copy.md')

How to loop over all files in a directory?¶

The following code prints all Python files in a given folder:

import os

for filename in os.listdir("/home/participant/"):
    if filename.endswith(".py"):
        print(filename)

How to run a command-line program from Python?¶

A very simple way to start other processes is the os.system() function. The following example starts a program to list contents of a folder and redirects the output to a file:

import os

os.system("ls -l > result.txt")

Warning

os.system does not allow for any communication with the running process. If it crashes or runs forever, your Python code won’t learn about it. A safer alternative is the subprocess module.