Essential File Operations

Read File Contents #

Read entire file #

# Method 1: Using with statement (recommended)
with open('file.txt', 'r') as f:
    content = f.read()
    print(content)

# Method 2: Using pathlib (modern approach)
from pathlib import Path
content = Path('file.txt').read_text()
print(content)

Read file line by line #

# Method 1: Iterate over file object
with open('file.txt', 'r') as f:
    for line in f:
        print(line.strip())  # strip() removes newline

# Method 2: Read all lines into list
with open('file.txt', 'r') as f:
    lines = f.readlines()
    for line in lines:
        print(line.strip())

# Method 3: Using pathlib
from pathlib import Path
lines = Path('file.txt').read_text().splitlines()
for line in lines:
    print(line)

Write to Files #

Write text to file #

# Overwrite existing file
with open('output.txt', 'w') as f:
    f.write('Hello, World!\n')
    f.write('Second line\n')

# Append to existing file
with open('output.txt', 'a') as f:
    f.write('Appended line\n')

# Using pathlib
from pathlib import Path
Path('output.txt').write_text('Hello, World!\n')

Write multiple lines #

lines = ['Line 1\n', 'Line 2\n', 'Line 3\n']

# Method 1
with open('output.txt', 'w') as f:
    f.writelines(lines)

# Method 2
with open('output.txt', 'w') as f:
    for line in lines:
        f.write(line)

# Method 3: Join and write
content = ''.join(lines)
with open('output.txt', 'w') as f:
    f.write(content)

Check File/Directory Existence #

import os
from pathlib import Path

# Check if file exists
if os.path.exists('file.txt'):
    print('File exists')

# Using pathlib (recommended)
file_path = Path('file.txt')
if file_path.exists():
    print('File exists')

# Check if it's a file vs directory
if file_path.is_file():
    print('It is a file')
elif file_path.is_dir():
    print('It is a directory')

Get File Information #

import os
from pathlib import Path

file_path = Path('file.txt')

# File size
size = file_path.stat().st_size
print(f'File size: {size} bytes')

# Last modified time
import datetime
modified_time = datetime.datetime.fromtimestamp(file_path.stat().st_mtime)
print(f'Last modified: {modified_time}')

# File extension
extension = file_path.suffix
print(f'Extension: {extension}')

# File name without extension
name = file_path.stem
print(f'Name: {name}')

Create Directories #

import os
from pathlib import Path

# Create single directory
os.makedirs('new_directory', exist_ok=True)

# Using pathlib
Path('new_directory').mkdir(exist_ok=True)

# Create nested directories
Path('parent/child/grandchild').mkdir(parents=True, exist_ok=True)

List Directory Contents #

import os
from pathlib import Path

# List all items
for item in os.listdir('.'):
    print(item)

# Using pathlib
for item in Path('.').iterdir():
    print(item.name)

# List only files
for item in Path('.').iterdir():
    if item.is_file():
        print(item.name)

# List files with specific extension
for item in Path('.').glob('*.py'):
    print(item.name)

Copy and Move Files #

import shutil
from pathlib import Path

# Copy file
shutil.copy2('source.txt', 'destination.txt')

# Copy entire directory
shutil.copytree('source_dir', 'destination_dir')

# Move/rename file
shutil.move('old_name.txt', 'new_name.txt')

# Using pathlib for rename
Path('old_name.txt').rename('new_name.txt')

Delete Files and Directories #

import os
import shutil
from pathlib import Path

# Delete file
os.remove('file.txt')
# or
Path('file.txt').unlink()

# Delete empty directory
os.rmdir('empty_directory')
# or
Path('empty_directory').rmdir()

# Delete directory and all contents
shutil.rmtree('directory_with_contents')

Safe File Operations with Error Handling #

from pathlib import Path

def safe_read_file(file_path):
    """Safely read a file with error handling."""
    try:
        path = Path(file_path)
        if not path.exists():
            return None, "File does not exist"
        
        content = path.read_text(encoding='utf-8')
        return content, None
    except PermissionError:
        return None, "Permission denied"
    except UnicodeDecodeError:
        return None, "Cannot decode file"
    except Exception as e:
        return None, f"Error reading file: {e}"

# Usage
content, error = safe_read_file('file.txt')
if error:
    print(f"Error: {error}")
else:
    print(content)

Working with CSV Files #

import csv
from pathlib import Path

# Read CSV
def read_csv(file_path):
    with open(file_path, 'r', newline='') as f:
        reader = csv.DictReader(f)
        return list(reader)

# Write CSV
def write_csv(file_path, data, fieldnames):
    with open(file_path, 'w', newline='') as f:
        writer = csv.DictWriter(f, fieldnames=fieldnames)
        writer.writeheader()
        writer.writerows(data)

# Example usage
data = [
    {'name': 'Alice', 'age': 30},
    {'name': 'Bob', 'age': 25}
]
write_csv('people.csv', data, ['name', 'age'])

Working with JSON Files #

import json
from pathlib import Path

# Read JSON
def read_json(file_path):
    with open(file_path, 'r') as f:
        return json.load(f)

# Write JSON
def write_json(file_path, data):
    with open(file_path, 'w') as f:
        json.dump(data, f, indent=2)

# Example usage
data = {'name': 'Alice', 'age': 30, 'city': 'New York'}
write_json('person.json', data)
loaded_data = read_json('person.json')