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gh-111881: Import _sha2 lazily in random (#111889)

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The random module now imports the _sha2 module lazily in the
Random.seed() method for str, bytes and bytearray seeds. It also
imports lazily the warnings module in the _randbelow() method for
classes without getrandbits(). Lazy import makes Python startup
faster and reduces the number of imported modules at startup.
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Victor Stinner 2023-11-09 23:10:21 +01:00 • committed by GitHub
parent 0802fd6c8e
commit b9f814ce6f
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1 changed files with 15 additions and 11 deletions
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26
Lib/random.py
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@ -50,7 +50,6 @@ General notes on the underlying Mersenne Twister core generator:
# Adrian Baddeley. Adapted by Raymond Hettinger for use with # Adrian Baddeley. Adapted by Raymond Hettinger for use with
# the Mersenne Twister and os.urandom() core generators. # the Mersenne Twister and os.urandom() core generators.
from warnings import warn as _warn
from math import log as _log, exp as _exp, pi as _pi, e as _e, ceil as _ceil from math import log as _log, exp as _exp, pi as _pi, e as _e, ceil as _ceil
from math import sqrt as _sqrt, acos as _acos, cos as _cos, sin as _sin from math import sqrt as _sqrt, acos as _acos, cos as _cos, sin as _sin
from math import tau as TWOPI, floor as _floor, isfinite as _isfinite from math import tau as TWOPI, floor as _floor, isfinite as _isfinite
@ -63,13 +62,6 @@ from bisect import bisect as _bisect
import os as _os import os as _os
import _random import _random
try:
# hashlib is pretty heavy to load, try lean internal module first
from _sha2 import sha512 as _sha512
except ImportError:
# fallback to official implementation
from hashlib import sha512 as _sha512
__all__ = [ __all__ = [
"Random", "Random",
"SystemRandom", "SystemRandom",
@ -105,6 +97,7 @@ SG_MAGICCONST = 1.0 + _log(4.5)
BPF = 53 # Number of bits in a float BPF = 53 # Number of bits in a float
RECIP_BPF = 2 ** -BPF RECIP_BPF = 2 ** -BPF
_ONE = 1 _ONE = 1
_sha512 = None
class Random(_random.Random): class Random(_random.Random):
@ -159,6 +152,16 @@ class Random(_random.Random):
a = -2 if x == -1 else x a = -2 if x == -1 else x
elif version == 2 and isinstance(a, (str, bytes, bytearray)): elif version == 2 and isinstance(a, (str, bytes, bytearray)):
global _sha512
if _sha512 is None:
try:
# hashlib is pretty heavy to load, try lean internal
# module first
from _sha2 import sha512 as _sha512
except ImportError:
# fallback to official implementation
from hashlib import sha512 as _sha512
if isinstance(a, str): if isinstance(a, str):
a = a.encode() a = a.encode()
a = int.from_bytes(a + _sha512(a).digest()) a = int.from_bytes(a + _sha512(a).digest())
@ -257,9 +260,10 @@ class Random(_random.Random):
random = self.random random = self.random
if n >= maxsize: if n >= maxsize:
_warn("Underlying random() generator does not supply \n" from warnings import warn
"enough bits to choose from a population range this large.\n" warn("Underlying random() generator does not supply \n"
"To remove the range limitation, add a getrandbits() method.") "enough bits to choose from a population range this large.\n"
"To remove the range limitation, add a getrandbits() method.")
return _floor(random() * n) return _floor(random() * n)
rem = maxsize % n rem = maxsize % n
limit = (maxsize - rem) / maxsize # int(limit * maxsize) % n == 0 limit = (maxsize - rem) / maxsize # int(limit * maxsize) % n == 0