Python os Module Essentials

import os
 
# Get variable
home = os.environ.get("HOME")
api_key = os.environ.get("API_KEY", "default")
 
# Set variable (current process only)
os.environ["MY_VAR"] = "value"
 
# Check if exists
if "DEBUG" in os.environ:
    debug_mode = True
 
# Get all
for key, value in os.environ.items():
    print(f"{key}={value}")

# Get current directory
cwd = os.getcwd()
 
# Change directory
os.chdir("/path/to/dir")
 
# Change and return (use contextlib for temp changes)
from contextlib import contextmanager
 
@contextmanager
def cd(path):
    old = os.getcwd()
    os.chdir(path)
    try:
        yield
    finally:
        os.chdir(old)
 
with cd("/tmp"):
    # Work in /tmp
    pass
# Back to original directory

import os.path
 
# Join paths
path = os.path.join("dir", "subdir", "file.txt")
 
# Split
dirname, filename = os.path.split("/path/to/file.txt")
# ("/path/to", "file.txt")
 
name, ext = os.path.splitext("file.txt")
# ("file", ".txt")
 
# Absolute path
os.path.abspath("relative/path")
 
# Normalize path
os.path.normpath("/path/../other/./file")  # "/other/file"
 
# Expand user
os.path.expanduser("~/documents")  # "/home/user/documents"
 
# Check paths
os.path.exists("/path/to/file")
os.path.isfile("/path/to/file")
os.path.isdir("/path/to/dir")
os.path.isabs("/absolute/path")

# List directory
files = os.listdir(".")
files = os.listdir("/path/to/dir")
 
# Create directory
os.mkdir("new_dir")
os.makedirs("path/to/nested/dir", exist_ok=True)
 
# Remove directory
os.rmdir("empty_dir")  # Must be empty
 
# Remove tree (use shutil)
import shutil
shutil.rmtree("dir_with_contents")

# Rename/move
os.rename("old_name.txt", "new_name.txt")
 
# Remove file
os.remove("file.txt")
os.unlink("file.txt")  # Same thing
 
# File info
stat = os.stat("file.txt")
stat.st_size   # Size in bytes
stat.st_mtime  # Modification time
stat.st_mode   # Permissions
 
# Check permissions
os.access("file.txt", os.R_OK)  # Readable?
os.access("file.txt", os.W_OK)  # Writable?
os.access("file.txt", os.X_OK)  # Executable?
 
# Change permissions
os.chmod("script.sh", 0o755)

# Walk all files recursively
for root, dirs, files in os.walk("."):
    for file in files:
        full_path = os.path.join(root, file)
        print(full_path)
    
    # Skip certain directories
    if ".git" in dirs:
        dirs.remove(".git")

# Platform
os.name          # "posix" or "nt"
os.uname()       # System info (Unix)
 
# User info
os.getuid()      # User ID (Unix)
os.getlogin()    # Login name
 
# Process info
os.getpid()      # Current process ID
os.getppid()     # Parent process ID
 
# CPU count
os.cpu_count()

import tempfile
 
# Get temp directory
temp_dir = tempfile.gettempdir()
 
# Create temp file
fd, path = tempfile.mkstemp(suffix=".txt")
os.close(fd)  # Close file descriptor
 
# Create temp directory
temp_dir = tempfile.mkdtemp()
 
# Context manager (auto-cleanup)
with tempfile.NamedTemporaryFile(delete=False) as f:
    f.write(b"data")
    temp_path = f.name

os.sep       # "/" on Unix, "\\" on Windows
os.pathsep   # ":" on Unix, ";" on Windows
os.linesep   # "\n" on Unix, "\r\n" on Windows

# Simple command (deprecated, use subprocess)
os.system("ls -la")
 
# Get output
stream = os.popen("ls")
output = stream.read()

def safe_remove(path):
    try:
        os.remove(path)
    except FileNotFoundError:
        pass

def ensure_dir(path):
    os.makedirs(path, exist_ok=True)

def find_files(directory, extension):
    for root, dirs, files in os.walk(directory):
        for file in files:
            if file.endswith(extension):
                yield os.path.join(root, file)
 
for py_file in find_files(".", ".py"):
    print(py_file)

def get_size(path):
    if os.path.isfile(path):
        return os.path.getsize(path)
    total = 0
    for root, dirs, files in os.walk(path):
        for file in files:
            total += os.path.getsize(os.path.join(root, file))
    return total

import os
 
# Environment
os.environ.get("VAR")
os.environ["VAR"] = "value"
 
# Paths
os.path.join("a", "b")
os.path.exists(path)
os.path.isfile(path)
os.path.isdir(path)
 
# Directories
os.getcwd()
os.chdir(path)
os.listdir(path)
os.makedirs(path, exist_ok=True)
 
# Files
os.remove(path)
os.rename(old, new)
os.stat(path)
 
# Walking
for root, dirs, files in os.walk(path):
    ...
 
# System
os.name
os.cpu_count()
os.getpid()