File Handling in Python

File handling refers to the process of performing operations on a file, such as creating, opening, reading, writing and closing it through a programming interface. It involves managing the data flow between the program and the file system on the storage device, ensuring that data is handled safely and efficiently.

Why do we need File Handling

• To store data permanently, even after the program ends.
• To access external files like .txt, .csv, .json, etc.
• To process large files efficiently without using much memory.
• To automate tasks like reading configs or saving outputs.
• To handle input/output in real-world applications and tools.

Opening a File

To open a file, we can use open() function, which requires file-path and mode as arguments:

Syntax:

file = open('filename.txt', 'mode')

• filename.txt: name (or path) of the file to be opened.
• mode: mode in which you want to open the file (read, write, append, etc.).

Note: If you don’t specify the mode, Python uses 'r' (read mode) by default.

Basic Example: Opening a File

f = open("geek.txt", "r")
print(f)

Explanation: This code opens file geek.txt in read mode. If the file exists, it returns a file object connected to that file; if the file does not exist, Python raises a FileNotFoundError.

Closing a File

The file.close() method closes the file and releases the system resources. If the file was opened in write or append mode, closing ensures that all changes are properly saved.

file = open("geek.txt", "r")
# Perform file operations
file.close()

We will also see later how closing can be handled automatically using the with statement and how to ensure files close properly using exception handling.

Checking File Properties

Once the file is open, we can check some of its properties:

f = open("geek.txt", "r")
print("Filename:", f.name)
print("Mode:", f.mode)
print("Is Closed?", f.closed)

f.close()
print("Is Closed?", f.closed)

Output:

Filename: geek.txt
Mode: r
Is Closed? False
Is Closed? True

Explanation:

• f.name: Returns the name of the file that was opened (in this case, "geek.txt").
• f.mode: Tells us the mode in which the file was opened. Here, it’s 'r' which means read mode.
• f.closed: Returns a boolean value- False when file is currently open otherwise True.

Reading a File

Reading a file can be achieved by file.read() which reads the entire content of the file. After reading, it’s good practice to close the file to free up system resources.

Example: Reading a File in Read Mode (r)

file = open("geek.txt", "r")
content = file.read()
print(content)
file.close()

Output:

Hello world
GeeksforGeeks
123 456

Writing a File

In Python, writing to a file is done using the mode "w". This creates a new file if it doesn’t exist, or overwrites the existing file if it does. The write() method is used to add content. After writing, make sure to close the file.

Example: Writing to a file (overwrites if file exists)

with open("geek.txt", "w") as file:
    file.write("Hello, Python!\n")
    file.write("File handling is easy with Python.")

print("File written successfully")

Output:

Hello, Python!
File handling is easy with Python.

Explanation:

• "w" mode opens the file for writing (overwrites existing content if the file already exists).
• write() method adds new text to the file.
• When using with, the file closes automatically at the end of the block.

Using with Statement

Instead of manually opening and closing the file, you can use the with statement, which automatically handles closing. This reduces the risk of file corruption and resource leakage.

Example: Let's assume we have a file named geek.txt that contains text "Hello, World!".

with open("geek.txt", "r") as file:
    content = file.read()
    print(content)

Output:

Hello, World!

Handling Exceptions When Closing a File

It's important to handle exceptions to ensure that files are closed properly, even if an error occurs during file operations. Here, the finally block ensures the file is closed even if an error occurs.

try:
    file = open("geek.txt", "r")
    content = file.read()
    print(content)
finally:
    file.close()

Output:

Hello, World!

Explanation:

• try: Starts the block to handle code that might raise an error.
• open(): Opens the file in read mode.
• read(): Reads the content of the file.
• finally: Ensures the code inside it runs no matter what.

Related articles: Modes in File Handling