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- """Generate cryptographically strong pseudo-random numbers suitable for
- managing secrets such as account authentication, tokens, and similar.
- See PEP 506 for more information.
- https://www.python.org/dev/peps/pep-0506/
- """
- __all__ = ['choice', 'randbelow', 'randbits', 'SystemRandom',
- 'token_bytes', 'token_hex', 'token_urlsafe',
- 'compare_digest',
- ]
- import base64
- import binascii
- import os
- from hmac import compare_digest
- from random import SystemRandom
- _sysrand = SystemRandom()
- randbits = _sysrand.getrandbits
- choice = _sysrand.choice
- def randbelow(exclusive_upper_bound):
- """Return a random int in the range [0, n)."""
- if exclusive_upper_bound <= 0:
- raise ValueError("Upper bound must be positive.")
- return _sysrand._randbelow(exclusive_upper_bound)
- DEFAULT_ENTROPY = 32 # number of bytes to return by default
- def token_bytes(nbytes=None):
- """Return a random byte string containing *nbytes* bytes.
- If *nbytes* is ``None`` or not supplied, a reasonable
- default is used.
- >>> token_bytes(16) #doctest:+SKIP
- b'\\xebr\\x17D*t\\xae\\xd4\\xe3S\\xb6\\xe2\\xebP1\\x8b'
- """
- if nbytes is None:
- nbytes = DEFAULT_ENTROPY
- return os.urandom(nbytes)
- def token_hex(nbytes=None):
- """Return a random text string, in hexadecimal.
- The string has *nbytes* random bytes, each byte converted to two
- hex digits. If *nbytes* is ``None`` or not supplied, a reasonable
- default is used.
- >>> token_hex(16) #doctest:+SKIP
- 'f9bf78b9a18ce6d46a0cd2b0b86df9da'
- """
- return binascii.hexlify(token_bytes(nbytes)).decode('ascii')
- def token_urlsafe(nbytes=None):
- """Return a random URL-safe text string, in Base64 encoding.
- The string has *nbytes* random bytes. If *nbytes* is ``None``
- or not supplied, a reasonable default is used.
- >>> token_urlsafe(16) #doctest:+SKIP
- 'Drmhze6EPcv0fN_81Bj-nA'
- """
- tok = token_bytes(nbytes)
- return base64.urlsafe_b64encode(tok).rstrip(b'=').decode('ascii')
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