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How to calculate the checksum of a file in Python

How to calculate the checksum of a file in Python.

Here's a step-by-step tutorial on how to calculate the checksum of a file in Python.

Step 1: Import the required modules​

To calculate the checksum of a file, we need to import the hashlib module, which provides various hashing algorithms.

import hashlib

Step 2: Open the file​

Next, we need to open the file for which we want to calculate the checksum. We can use the open() function in Python to do this. It takes two arguments - the filename and the mode in which the file should be opened. We will open the file in binary mode ('rb') to ensure that the file is read as binary data.

filename = 'path/to/your/file.ext'
with open(filename, 'rb') as file:
    # Code for checksum calculation goes here

Replace 'path/to/your/file.ext' with the actual path to your file.

Step 3: Initialize the hashing algorithm​

To calculate the checksum, we need to initialize the hashing algorithm. We can choose from various algorithms provided by the hashlib module, such as MD5, SHA-1, SHA-256, etc. In this example, we'll use the SHA-256 algorithm.

hash_algorithm = hashlib.sha256()

Step 4: Read the file in blocks and update the checksum​

To calculate the checksum, we'll read the file in blocks and update the checksum for each block. This is useful for large files, as it avoids loading the entire file into memory at once.

block_size = 4096
for block in iter(lambda: file.read(block_size), b''):
    hash_algorithm.update(block)

Here, block_size represents the size of each block. You can choose a suitable value based on your requirements.

Step 5: Get the final checksum​

After reading the entire file and updating the checksum, we can get the final checksum value using the hexdigest() method.

checksum = hash_algorithm.hexdigest()
print(f"The checksum of {filename} is: {checksum}")

The hexdigest() method returns the checksum as a hexadecimal string.

Complete code example​

Here's the complete code example that you can use to calculate the checksum of a file:

import hashlib

filename = 'path/to/your/file.ext'
hash_algorithm = hashlib.sha256()

with open(filename, 'rb') as file:
    block_size = 4096
    for block in iter(lambda: file.read(block_size), b''):
        hash_algorithm.update(block)

checksum = hash_algorithm.hexdigest()
print(f"The checksum of {filename} is: {checksum}")

Replace 'path/to/your/file.ext' with the actual path to your file.

That's it! You've successfully calculated the checksum of a file in Python.