Python File Methods

📖 Reading Methods

Different ways to read content from files

🔹 read() - Read All Content

# Read entire file at once
with open("story.txt", "r") as file:
    content = file.read()
    print(f"File content: {content}")
    print(f"Content length: {len(content)} characters")

# Read specific number of characters
with open("story.txt", "r") as file:
    first_10_chars = file.read(10)
    print(f"First 10 characters: {first_10_chars}")

🔹 readline() - Read One Line

# Read one line at a time
with open("names.txt", "r") as file:
    first_line = file.readline()
    second_line = file.readline()
    print(f"First name: {first_line.strip()}")
    print(f"Second name: {second_line.strip()}")

# Read lines in a loop
with open("names.txt", "r") as file:
    line_number = 1
    while True:
        line = file.readline()
        if not line:  # End of file
            break
        print(f"Line {line_number}: {line.strip()}")
        line_number += 1

🔹 readlines() - Read All Lines

# Read all lines into a list
with open("shopping.txt", "r") as file:
    items = file.readlines()
    print("Shopping list:")
    for i, item in enumerate(items, 1):
        print(f"{i}. {item.strip()}")

# Process each line
with open("numbers.txt", "r") as file:
    lines = file.readlines()
    numbers = [int(line.strip()) for line in lines]
    print(f"Sum of numbers: {sum(numbers)}")

✏️ Writing Methods

Different ways to write content to files

🔹 write() - Write String

# Write a single string
with open("output.txt", "w") as file:
    file.write("Hello, World!")
    file.write("\nThis is line 2")

# Write with formatting
name = "Alice"
age = 25
with open("profile.txt", "w") as file:
    file.write(f"Name: {name}\n")
    file.write(f"Age: {age}\n")
    
# Append to existing file
with open("log.txt", "a") as file:
    file.write("New log entry\n")

🔹 writelines() - Write List of Strings

# Write multiple lines at once
fruits = ["apple\n", "banana\n", "cherry\n"]
with open("fruits.txt", "w") as file:
    file.writelines(fruits)

# Write processed data
numbers = [1, 2, 3, 4, 5]
with open("squares.txt", "w") as file:
    lines = [f"{n} squared is {n**2}\n" for n in numbers]
    file.writelines(lines)

🔹 flush() - Force Write to Disk

# Ensure data is written immediately
with open("important.txt", "w") as file:
    file.write("Critical data")
    file.flush()  # Force write to disk now
    print("Data safely written!")

# Useful for real-time logging
import time
with open("realtime.log", "w") as file:
    for i in range(5):
        file.write(f"Event {i} at {time.time()}\n")
        file.flush()  # Write immediately
        time.sleep(1)

🎯 Position Methods

Navigate and control position within files

🔹 seek() - Move to Position

# Move to specific position
with open("data.txt", "r") as file:
    file.seek(0)    # Go to beginning
    first_char = file.read(1)
    
    file.seek(5)    # Go to position 5
    next_chars = file.read(3)
    
    print(f"First character: {first_char}")
    print(f"Characters 5-7: {next_chars}")

# Go to end of file
with open("data.txt", "r") as file:
    file.seek(0, 2)  # 2 means from end
    file_size = file.tell()
    print(f"File size: {file_size} bytes")

🔹 tell() - Get Current Position

# Track position while reading
with open("story.txt", "r") as file:
    print(f"Start position: {file.tell()}")
    
    first_line = file.readline()
    print(f"After first line: {file.tell()}")
    
    file.read(10)
    print(f"After reading 10 chars: {file.tell()}")

# Save and restore position
with open("data.txt", "r") as file:
    saved_position = file.tell()
    content = file.read(20)
    file.seek(saved_position)  # Go back
    same_content = file.read(20)
    print(f"Same content: {content == same_content}")

🔧 File Control Methods

Manage file state and properties

🔹 File Properties

# Check file properties
with open("example.txt", "r") as file:
    print(f"File name: {file.name}")
    print(f"File mode: {file.mode}")
    print(f"Is closed: {file.closed}")
    print(f"Is readable: {file.readable()}")
    print(f"Is writable: {file.writable()}")

# After closing
print(f"After context: {file.closed}")  # True

🔹 Manual File Handling

# Manual open/close (not recommended)
file = open("manual.txt", "w")
file.write("Manual handling")
print(f"Is closed: {file.closed}")  # False
file.close()
print(f"Is closed: {file.closed}")  # True

# Better: Use context manager
with open("auto.txt", "w") as file:
    file.write("Automatic handling")
# File automatically closed here

📋 File Modes

Different ways to open files

# Different file modes
# Read mode
with open("data.txt", "r") as file:
    content = file.read()

# Write mode (creates new or overwrites)
with open("output.txt", "w") as file:
    file.write("New content")

# Append mode (adds to end)
with open("log.txt", "a") as file:
    file.write("New log entry\n")

# Read and write mode
with open("data.txt", "r+") as file:
    content = file.read()
    file.write("\nAdded text")

# Binary mode for images, etc.
with open("image.jpg", "rb") as file:
    binary_data = file.read()
    print(f"File size: {len(binary_data)} bytes")

🛡️ Safe File Handling

Best practices for working with files

# Always use context managers
def safe_read_file(filename):
    """Safely read a file with error handling"""
    try:
        with open(filename, "r") as file:
            return file.read()
    except FileNotFoundError:
        return f"File {filename} not found"
    except PermissionError:
        return f"No permission to read {filename}"
    except Exception as e:
        return f"Error reading file: {e}"

# Test the function
content = safe_read_file("example.txt")
print(content)

# Check if file exists before opening
import os

def process_file(filename):
    """Process file only if it exists"""
    if os.path.exists(filename):
        with open(filename, "r") as file:
            lines = file.readlines()
            print(f"File has {len(lines)} lines")
    else:
        print(f"File {filename} does not exist")

process_file("data.txt")

# Create backup before writing
def safe_write_file(filename, content):
    """Write file with backup"""
    if os.path.exists(filename):
        # Create backup
        with open(filename, "r") as original:
            backup_content = original.read()
        with open(f"{filename}.backup", "w") as backup:
            backup.write(backup_content)
    
    # Write new content
    with open(filename, "w") as file:
        file.write(content)
    print(f"File {filename} updated safely")

safe_write_file("important.txt", "New important data")