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):