os.path.join() / os.path.exists() / os.path.basename()

import os

# Joins path components together.
os.path.join(path1, path2, ...)

# Checks whether a file or directory exists.
os.path.exists(path)

# Returns the last component of a path (the filename).
os.path.basename(path)

# Returns the directory portion of a path.
os.path.dirname(path)

# Splits a path into the filename and extension.
os.path.splitext(path)

# Converts a path to an absolute path.
os.path.abspath(path)

import os

# Use join() to build a path safely.
base_dir = '/Users/user/documents'
filename = 'report.txt'
full_path = os.path.join(base_dir, 'reports', filename)
print(full_path)  # Outputs: /Users/user/documents/reports/report.txt

# Use exists() to check whether a file exists.
print(os.path.exists('/Users/user/documents'))  # Outputs True if it exists.
print(os.path.exists('/nonexistent/path'))       # Outputs False.

# Use basename() and dirname() to decompose a path.
path = '/var/www/html/index.php'
print(os.path.basename(path))  # Outputs: index.php
print(os.path.dirname(path))   # Outputs: /var/www/html

# Use splitext() to extract the file extension.
name, ext = os.path.splitext('photo.jpg')
print(name)  # Outputs: photo
print(ext)   # Outputs: .jpg

# Generate a new filename with a different extension.
src = 'document.txt'
dst = os.path.splitext(src)[0] + '.md'
print(dst)  # Outputs: document.md

# Use abspath() to get the absolute path.
print(os.path.abspath('.'))         # Outputs the absolute path of the current directory.
print(os.path.abspath('../data'))   # Converts the relative path to an absolute path.

# Use isfile() and isdir() to check the type.
print(os.path.isfile('/etc/hosts'))   # Outputs True if it is a file.
print(os.path.isdir('/etc'))          # Outputs True if it is a directory.

os.path.join() uses the OS-appropriate separator (backslash \ on Windows, forward slash / on Mac/Linux) to join paths. Building paths with string concatenation (the + operator) can break across environments, so always use os.path.join() for safe, portable code.

Since Python 3.4, the pathlib module provides the same functionality in a more object-oriented style. New code is encouraged to use pathlib.Path. That said, os.path remains widely used for compatibility with existing code and third-party libraries.

For modern path handling, see pathlib.Path(). For directory operations, see os.listdir() / os.makedirs() / os.remove().