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hashlib

The hashlib library provides cryptographic hash functions (MD5, SHA-1, SHA-256). Its constructors return hash objects rather than raw strings: call .hexdigest() (lowercase hex) or .digest() (raw binary as a bytes value) on the returned object to get the result.

Available Functions

Function Description
md5([data]) Create an MD5 hash object.
sha1([data]) Create a SHA-1 hash object.
sha256([data]) Create a SHA-256 hash object.

Functions

sha256([data])

Creates a SHA-256 hash object, optionally seeded with data.

Parameters:

  • data (str, bytes, or list, optional): Initial data to hash: a string (encoded as UTF-8), a bytes value, or a list of byte values (as returned by str.encode()).

Returns: Hash: an instance supporting .update(), .hexdigest(), .digest(), and .copy() (see Hash Object Methods below).

import hashlib

h = hashlib.sha256("hello")
print(h.hexdigest())  # "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
print(h.name)         # "sha256"
print(h.digest_size)  # 32

sha1([data])

Creates a SHA-1 hash object, optionally seeded with data.

Parameters:

  • data (str or list, optional): Initial data to hash.

Returns: Hash: .hexdigest() is 40 hex characters.

import hashlib

print(hashlib.sha1("hello").hexdigest())  # "aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d"

md5([data])

Creates an MD5 hash object, optionally seeded with data.

Parameters:

  • data (str or list, optional): Initial data to hash.

Returns: Hash: .hexdigest() is 32 hex characters.

import hashlib

print(hashlib.md5("hello").hexdigest())  # "5d41402abc4b2a76b9719d911017c592"

Hash Object Methods

Objects returned by md5(), sha1(), and sha256() support:

Method / Field Description
.update(data) Feed more data into the hash. Returns None.
.hexdigest() Return the digest as a lowercase hex string.
.digest() Return the digest as a bytes value.
.copy() Return an independent copy of the hash object.
.name Algorithm name, e.g. "sha256".
.digest_size Digest size in bytes (md5 16, sha1 20, sha256 32).
.block_size Block size in bytes (64 for all supported algorithms). 
import hashlib

# Build a hash incrementally
h = hashlib.sha256()
h.update("foo")
h.update("bar")
assert h.hexdigest() == hashlib.sha256("foobar").hexdigest()

# copy() is independent
c = h.copy()
h.update("baz")
assert c.hexdigest() == hashlib.sha256("foobar").hexdigest()
assert h.hexdigest() == hashlib.sha256("foobarbaz").hexdigest()

See Also

  • hmac: message authentication codes, often paired with hashlib constructors.
  • base64: Base64 encoding and decoding.
  • bytes: the binary type returned by .digest().