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

The random module now imports the _sha2 module lazily in theRandom.seed() method for str, bytes and bytearray seeds. It alsoimports lazily the warnings module in the _randbelow() method forclasses without getrandbits(). Lazy import makes Python startupfaster and reduces the number of imported modules at startup.

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`‎Lib/random.py`

Lines changed: 15 additions & 11 deletions

Original file line number	Diff line number	Diff line change
`@@ -50,7 +50,6 @@`
`50`	`50`	`# Adrian Baddeley. Adapted by Raymond Hettinger for use with`
`51`	`51`	`# the Mersenne Twister and os.urandom() core generators.`
`52`	`52`
`53`		`-fromwarningsimportwarnas_warn`
`54`	`53`	`frommathimportlogas_log,expas_exp,pias_pi,eas_e,ceilas_ceil`
`55`	`54`	`frommathimportsqrtas_sqrt,acosas_acos,cosas_cos,sinas_sin`
`56`	`55`	`frommathimporttauasTWOPI,flooras_floor,isfiniteas_isfinite`
`@@ -63,13 +62,6 @@`
`63`	`62`	`importosas_os`
`64`	`63`	`import_random`
`65`	`64`
`66`		`-try:`
`67`		`-# hashlib is pretty heavy to load, try lean internal module first`
`68`		`-from_sha2importsha512as_sha512`
`69`		`-exceptImportError:`
`70`		`-# fallback to official implementation`
`71`		`-fromhashlibimportsha512as_sha512`
`72`		`-`
`73`	`65`	`__all__= [`
`74`	`66`	`"Random",`
`75`	`67`	`"SystemRandom",`
`@@ -105,6 +97,7 @@`
`105`	`97`	`BPF=53# Number of bits in a float`
`106`	`98`	`RECIP_BPF=2**-BPF`
`107`	`99`	`_ONE=1`
	`100`	`+_sha512=None`
`108`	`101`
`109`	`102`
`110`	`103`	`classRandom(_random.Random):`
`@@ -159,6 +152,16 @@ def seed(self, a=None, version=2):`
`159`	`152`	`a=-2ifx==-1elsex`
`160`	`153`
`161`	`154`	`elifversion==2andisinstance(a, (str,bytes,bytearray)):`
	`155`	`+global_sha512`
	`156`	`+if_sha512isNone:`
	`157`	`+try:`
	`158`	`+# hashlib is pretty heavy to load, try lean internal`
	`159`	`+# module first`
	`160`	`+from_sha2importsha512as_sha512`
	`161`	`+exceptImportError:`
	`162`	`+# fallback to official implementation`
	`163`	`+fromhashlibimportsha512as_sha512`
	`164`	`+`
`162`	`165`	`ifisinstance(a,str):`
`163`	`166`	`a=a.encode()`
`164`	`167`	`a=int.from_bytes(a+_sha512(a).digest())`
`@@ -257,9 +260,10 @@ def _randbelow_without_getrandbits(self, n, maxsize=1<<BPF):`
`257`	`260`
`258`	`261`	`random=self.random`
`259`	`262`	`ifn>=maxsize:`
`260`		`-_warn("Underlying random() generator does not supply\n"`
`261`		`-"enough bits to choose from a population range this large.\n"`
`262`		`-"To remove the range limitation, add a getrandbits() method.")`
	`263`	`+fromwarningsimportwarn`
	`264`	`+warn("Underlying random() generator does not supply\n"`
	`265`	`+"enough bits to choose from a population range this large.\n"`
	`266`	`+"To remove the range limitation, add a getrandbits() method.")`
`263`	`267`	`return_floor(random()*n)`
`264`	`268`	`rem=maxsize%n`
`265`	`269`	`limit= (maxsize-rem)/maxsize# int(limit * maxsize) % n == 0`

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`‎Lib/random.py`

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