Teach the random module about os.urandom().
* Use it for seeding when it is available.
* Provide an alternate generator based on it.
diff --git a/Lib/random.py b/Lib/random.py
index 7ec6583..06990d2 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -49,7 +49,8 @@
"randrange","shuffle","normalvariate","lognormvariate",
"expovariate","vonmisesvariate","gammavariate",
"gauss","betavariate","paretovariate","weibullvariate",
- "getstate","setstate","jumpahead", "WichmannHill", "getrandbits"]
+ "getstate","setstate","jumpahead", "WichmannHill", "getrandbits",
+ "HardwareRandom"]
NV_MAGICCONST = 4 * _exp(-0.5)/_sqrt(2.0)
TWOPI = 2.0*_pi
@@ -57,6 +58,15 @@
SG_MAGICCONST = 1.0 + _log(4.5)
BPF = 53 # Number of bits in a float
+try:
+ from os import urandom as _urandom
+ from binascii import hexlify as _hexlify
+except ImportError:
+ _urandom = None
+else:
+ _tofloat = 2.0 ** (-7*8) # converts 7 byte integers to floats
+
+
# Translated by Guido van Rossum from C source provided by
# Adrian Baddeley. Adapted by Raymond Hettinger for use with
# the Mersenne Twister core generator.
@@ -94,14 +104,19 @@
def seed(self, a=None):
"""Initialize internal state from hashable object.
- None or no argument seeds from current time.
+ None or no argument seeds from current time or from a hardware
+ randomness source if available.
If a is not None or an int or long, hash(a) is used instead.
"""
if a is None:
- import time
- a = long(time.time() * 256) # use fractional seconds
+ if _urandom is None:
+ import time
+ a = long(time.time() * 256) # use fractional seconds
+ else:
+ a = long(_hexlify(_urandom(16)), 16)
+
super(Random, self).seed(a)
self.gauss_next = None
@@ -593,7 +608,8 @@
def seed(self, a=None):
"""Initialize internal state from hashable object.
- None or no argument seeds from current time.
+ None or no argument seeds from current time or from a hardware
+ randomness source if available.
If a is not None or an int or long, hash(a) is used instead.
@@ -604,9 +620,11 @@
"""
if a is None:
- # Initialize from current time
- import time
- a = long(time.time() * 256)
+ if _urandom is None:
+ import time
+ a = long(time.time() * 256) # use fractional seconds
+ else:
+ a = long(_hexlify(_urandom(16)), 16)
if not isinstance(a, (int, long)):
a = hash(a)
@@ -731,6 +749,42 @@
z = (z + a) % 256 or 1
self.__whseed(x, y, z)
+## -------------------- Hardware Random Source -------------------
+
+class HardwareRandom(Random):
+ """Alternate random number generator using hardware sources.
+
+ Not available on all systems (see os.urandom() for details).
+ """
+
+ def random(self):
+ """Get the next random number in the range [0.0, 1.0)."""
+ if _urandom is None:
+ raise NotImplementedError('Cannot find hardware entropy source')
+ return long(_hexlify(_urandom(7)), 16) * _tofloat
+
+ def getrandbits(self, k):
+ """getrandbits(k) -> x. Generates a long int with k random bits."""
+ if _urandom is None:
+ raise NotImplementedError('Cannot find hardware entropy source')
+ if k <= 0:
+ raise ValueError('number of bits must be greater than zero')
+ if k != int(k):
+ raise TypeError('number of bits should be an integer')
+ bytes = (k + 7) // 8 # bits / 8 and rounded up
+ x = long(_hexlify(_urandom(bytes)), 16)
+ return x >> (bytes * 8 - k) # trim excess bits
+
+ def _stub(self, *args, **kwds):
+ "Stub method. Not used for a hardware random number generator."
+ return None
+ seed = jumpahead = _stub
+
+ def _notimplemented(self, *args, **kwds):
+ "Method should not be called for a hardware random number generator."
+ raise NotImplementedError('Hardware entropy source does not have state.')
+ getstate = setstate = _notimplemented
+
## -------------------- test program --------------------
def _test_generator(n, func, args):
diff --git a/Lib/test/test_random.py b/Lib/test/test_random.py
index ead0dca..0396e58 100644
--- a/Lib/test/test_random.py
+++ b/Lib/test/test_random.py
@@ -164,6 +164,107 @@
self.assertRaises(UserWarning, self.gen.randrange, 2**60)
warnings.filters[:] = oldfilters
+class HardwareRandom_TestBasicOps(TestBasicOps):
+ gen = random.HardwareRandom()
+
+ def test_autoseed(self):
+ # Doesn't need to do anything except not fail
+ self.gen.seed()
+
+ def test_saverestore(self):
+ self.assertRaises(NotImplementedError, self.gen.getstate)
+ self.assertRaises(NotImplementedError, self.gen.setstate, None)
+
+ def test_seedargs(self):
+ # Doesn't need to do anything except not fail
+ self.gen.seed(100)
+
+ def test_jumpahead(self):
+ # Doesn't need to do anything except not fail
+ self.gen.jumpahead(100)
+
+ def test_gauss(self):
+ self.gen.gauss_next = None
+ self.gen.seed(100)
+ self.assertEqual(self.gen.gauss_next, None)
+
+ def test_pickling(self):
+ self.assertRaises(NotImplementedError, pickle.dumps, self.gen)
+
+ def test_53_bits_per_float(self):
+ # This should pass whenever a C double has 53 bit precision.
+ span = 2 ** 53
+ cum = 0
+ for i in xrange(100):
+ cum |= int(self.gen.random() * span)
+ self.assertEqual(cum, span-1)
+
+ def test_bigrand(self):
+ # The randrange routine should build-up the required number of bits
+ # in stages so that all bit positions are active.
+ span = 2 ** 500
+ cum = 0
+ for i in xrange(100):
+ r = self.gen.randrange(span)
+ self.assert_(0 <= r < span)
+ cum |= r
+ self.assertEqual(cum, span-1)
+
+ def test_bigrand_ranges(self):
+ for i in [40,80, 160, 200, 211, 250, 375, 512, 550]:
+ start = self.gen.randrange(2 ** i)
+ stop = self.gen.randrange(2 ** (i-2))
+ if stop <= start:
+ return
+ self.assert_(start <= self.gen.randrange(start, stop) < stop)
+
+ def test_rangelimits(self):
+ for start, stop in [(-2,0), (-(2**60)-2,-(2**60)), (2**60,2**60+2)]:
+ self.assertEqual(set(range(start,stop)),
+ set([self.gen.randrange(start,stop) for i in xrange(100)]))
+
+ def test_genrandbits(self):
+ # Verify ranges
+ for k in xrange(1, 1000):
+ self.assert_(0 <= self.gen.getrandbits(k) < 2**k)
+
+ # Verify all bits active
+ getbits = self.gen.getrandbits
+ for span in [1, 2, 3, 4, 31, 32, 32, 52, 53, 54, 119, 127, 128, 129]:
+ cum = 0
+ for i in xrange(100):
+ cum |= getbits(span)
+ self.assertEqual(cum, 2**span-1)
+
+ # Verify argument checking
+ self.assertRaises(TypeError, self.gen.getrandbits)
+ self.assertRaises(TypeError, self.gen.getrandbits, 1, 2)
+ self.assertRaises(ValueError, self.gen.getrandbits, 0)
+ self.assertRaises(ValueError, self.gen.getrandbits, -1)
+ self.assertRaises(TypeError, self.gen.getrandbits, 10.1)
+
+ def test_randbelow_logic(self, _log=log, int=int):
+ # check bitcount transition points: 2**i and 2**(i+1)-1
+ # show that: k = int(1.001 + _log(n, 2))
+ # is equal to or one greater than the number of bits in n
+ for i in xrange(1, 1000):
+ n = 1L << i # check an exact power of two
+ numbits = i+1
+ k = int(1.00001 + _log(n, 2))
+ self.assertEqual(k, numbits)
+ self.assert_(n == 2**(k-1))
+
+ n += n - 1 # check 1 below the next power of two
+ k = int(1.00001 + _log(n, 2))
+ self.assert_(k in [numbits, numbits+1])
+ self.assert_(2**k > n > 2**(k-2))
+
+ n -= n >> 15 # check a little farther below the next power of two
+ k = int(1.00001 + _log(n, 2))
+ self.assertEqual(k, numbits) # note the stronger assertion
+ self.assert_(2**k > n > 2**(k-1)) # note the stronger assertion
+
+
class MersenneTwister_TestBasicOps(TestBasicOps):
gen = random.Random()
@@ -391,6 +492,7 @@
def test_main(verbose=None):
testclasses = (WichmannHill_TestBasicOps,
MersenneTwister_TestBasicOps,
+ HardwareRandom_TestBasicOps,
TestDistributions,
TestModule)
test_support.run_unittest(*testclasses)