File Handling in Python

File handling in Python allows you to work with files—reading, writing, appending, and managing data stored in files. Python provides built-in functions and methods for file handling, making it easy to manage files and directories.

Basics of File Handling

1. Opening a File
   Use the open() function to open a file.

   file = open("filename", mode)
   

   • filename: Name or path of the file.
   • mode: Specifies the mode for file operations:
     • 'r': Read (default).
     • 'w': Write (creates/overwrites the file).
     • 'a': Append (adds to the file if it exists).
     • 'x': Create (fails if the file exists).
     • 'b': Binary mode (e.g., 'rb', 'wb').
     • 't': Text mode (default, e.g., 'rt').

2. Closing a File
   Always close files after use to release resources:

   file.close()
   

3. Using with Statement
   The with statement ensures files are properly closed after their block of code is executed:

   with open("filename", "mode") as file:
       # Perform file operations
   

Common File Operations

1. Reading from a File

# Read the entire file
with open("example.txt", "r") as file:
    content = file.read()
    print(content)

# Read line by line
with open("example.txt", "r") as file:
    for line in file:
        print(line.strip())

2. Writing to a File

# Write to a new or existing file (overwrites content)
with open("example.txt", "w") as file:
    file.write("This is a new line.\n")
    file.write("Another line.\n")

3. Appending to a File

# Add content to an existing file
with open("example.txt", "a") as file:
    file.write("This line is appended.\n")

File Methods

• read(size): Reads size characters or bytes (default is the entire file).
• readline(): Reads a single line from the file.
• readlines(): Reads all lines as a list.
• write(string): Writes a string to the file.
• writelines(lines): Writes a list of strings to the file.

Copying Content from One File to Another

with open("source.txt", "r") as source:
    content = source.read()

with open("destination.txt", "w") as destination:
    destination.write(content)

Checking File Existence

Use the os module to check if a file exists:

import os

if os.path.exists("example.txt"):
    print("File exists.")
else:
    print("File does not exist.")

Modes Summary