Python Language Tutorial => File Hashing

Example

A hash is a function that converts a variable length sequence of bytes to a fixed length sequence. Hashing files can be advantageous for many reasons. Hashes can be used to check if two files are identical or verify that the contents of a file haven't been corrupted or changed.

You can use hashlib to generate a hash for a file:

import hashlib

hasher = hashlib.new('sha256')
with open('myfile', 'r') as f:
    contents = f.read()
    hasher.update(contents)

print hasher.hexdigest()

For larger files, a buffer of fixed length can be used:

import hashlib
SIZE = 65536
hasher = hashlib.new('sha256')
with open('myfile', 'r') as f:
    buffer = f.read(SIZE)
    while len(buffer) > 0:
        hasher.update(buffer)
        buffer = f.read(SIZE)
print(hasher.hexdigest())

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Python Language Security and Cryptography File Hashing

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