`hashlib`

The Python hashlib module provides a common interface to many secure hash and message digest algorithms, such as SHA-256 and MD5.

These algorithms allow you to generate fixed-size hash values from arbitrary input data, which is useful for data integrity checks, password storage, and more.

Here’s a quick example:

Python
      
>>> import hashlib
>>> hashlib.sha256(b"Real Python").hexdigest()
'4a2b42c72ead91c16165d81622a347d5d65addb3a6984927b8322af26827baf3'

Key Features

Provides a common API for many hash algorithms
Supports secure hash functions like SHA-256, SHA-512, and others
Includes the MD5 algorithm for legacy purposes
Allows creating hash objects for iterative data feeding

Frequently Used Classes and Functions

Object	Type	Description
`hashlib.new()`	Function	Creates a hash object for a given algorithm name
`hashlib.sha256()`	Function	Creates a SHA-256 hash object
`hashlib.md5()`	Function	Creates an MD5 hash object
`hashlib.algorithms_guaranteed`	Constant	Set of algorithms guaranteed to be supported

Examples

Using md5 for a quick checksum (not secure for cryptographic purposes):

Python
      
>>> hash_object = hashlib.md5(b"Real Python")
>>> hash_object.hexdigest()
'5245ae598714e551418aa6d5cc2cf5bc'

Iteratively updating a hash object:

Python
      
        
      
    
>>> hash_object = hashlib.sha256()
>>> hash_object.update(b"Real ")
>>> hash_object.update(b"Python")
>>> hash_object.hexdigest()
'4a2b42c72ead91c16165d81622a347d5d65addb3a6984927b8322af26827baf3'

Common Use Cases

Verifying data integrity with checksums
Storing passwords securely using dedicated password hashing algorithms
Creating unique identifiers for data

Real-World Example

Suppose you want to verify the integrity of a downloaded file by comparing its SHA-256 hash to a known value. Here’s how you could accomplish this using hashlib:

Python
      
        
      
    
>>> import hashlib

>>> def calculate_file_hash(file_path):
...     hash_obj = hashlib.sha256()
...     with open(file_path, "rb") as file:
...         while chunk := file.read(8192):
...             hash_obj.update(chunk)
...     return hash_obj.hexdigest()

>>> known_hash = "expected_sha256_hash_value"
>>> file_hash = calculate_file_hash("downloaded_file.txt")
>>> file_hash == known_hash
True

In this example, you use hashlib to compute the SHA-256 hash of a file in chunks, ensuring efficient memory usage for large files. This allows you to verify the file’s integrity by comparing the computed hash to a known value.

Tutorial

Build a Hash Table in Python With TDD

In this step-by-step tutorial, you'll implement the classic hash table data structure using Python. Along the way, you'll learn how to cope with various challenges such as hash code collisions while practicing test-driven development (TDD).

intermediate data-structures

By Leodanis Pozo Ramos • Updated July 9, 2025

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hashlib