Change random.seed() so that it can get at the full range of possible
internal states. Put the old .seed() (which could only get at about
the square root of the # of possibilities) under the new name .whseed(),
for bit-level compatibility with older versions. This occurred to me
while reviewing effbot's book (he found himself stumbling over .seed()
more than once there ...).
diff --git a/Lib/random.py b/Lib/random.py
index b9359e4..427b731 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -66,10 +66,10 @@
>>> g = Random(42) # arbitrary
>>> g.random()
-0.24855401895528142
+0.25420336316883324
>>> g.jumpahead(6953607871644L - 1) # move *back* one
>>> g.random()
-0.24855401895528142
+0.25420336316883324
"""
# XXX The docstring sucks.
@@ -119,26 +119,31 @@
# different core generator should override the seed(), random(),
# getstate(), setstate() and jumpahead() methods.
- def __whseed(self, x=0, y=0, z=0):
- """Set the Wichmann-Hill seed from (x, y, z).
+ def seed(self, a=None):
+ """Initialize internal state from hashable object.
- These must be integers in the range [0, 256).
+ None or no argument seeds from current time.
+
+ If a is not None or an int or long, hash(a) is instead.
+
+ If a is an int or long, a is used directly. Distinct values between
+ 0 and 27814431486575L inclusive are guaranteed to yield distinct
+ internal states (this guarantee is specific to the default
+ Wichmann-Hill generator).
"""
- if not type(x) == type(y) == type(z) == type(0):
- raise TypeError('seeds must be integers')
- if not (0 <= x < 256 and 0 <= y < 256 and 0 <= z < 256):
- raise ValueError('seeds must be in range(0, 256)')
- if 0 == x == y == z:
+ if a is None:
# Initialize from current time
import time
- t = long(time.time()) * 256
- t = int((t&0xffffff) ^ (t>>24))
- t, x = divmod(t, 256)
- t, y = divmod(t, 256)
- t, z = divmod(t, 256)
- # Zero is a poor seed, so substitute 1
- self._seed = (x or 1, y or 1, z or 1)
+ a = long(time.time() * 256)
+
+ if type(a) not in (type(3), type(3L)):
+ a = hash(a)
+
+ a, x = divmod(a, 30268)
+ a, y = divmod(a, 30306)
+ a, z = divmod(a, 30322)
+ self._seed = int(x)+1, int(y)+1, int(z)+1
def random(self):
"""Get the next random number in the range [0.0, 1.0)."""
@@ -171,26 +176,6 @@
# never return 0.0 (asserted by Tim; proof too long for a comment).
return (x/30269.0 + y/30307.0 + z/30323.0) % 1.0
- def seed(self, a=None):
- """Seed from hashable object's hash code.
-
- None or no argument seeds from current time. It is not guaranteed
- that objects with distinct hash codes lead to distinct internal
- states.
- """
-
- if a is None:
- self.__whseed()
- return
- a = hash(a)
- a, x = divmod(a, 256)
- a, y = divmod(a, 256)
- a, z = divmod(a, 256)
- x = (x + a) % 256 or 1
- y = (y + a) % 256 or 1
- z = (z + a) % 256 or 1
- self.__whseed(x, y, z)
-
def getstate(self):
"""Return internal state; can be passed to setstate() later."""
return self.VERSION, self._seed, self.gauss_next
@@ -227,6 +212,50 @@
z = int(z * pow(170, n, 30323)) % 30323
self._seed = x, y, z
+ def __whseed(self, x=0, y=0, z=0):
+ """Set the Wichmann-Hill seed from (x, y, z).
+
+ These must be integers in the range [0, 256).
+ """
+
+ if not type(x) == type(y) == type(z) == type(0):
+ raise TypeError('seeds must be integers')
+ if not (0 <= x < 256 and 0 <= y < 256 and 0 <= z < 256):
+ raise ValueError('seeds must be in range(0, 256)')
+ if 0 == x == y == z:
+ # Initialize from current time
+ import time
+ t = long(time.time() * 256)
+ t = int((t&0xffffff) ^ (t>>24))
+ t, x = divmod(t, 256)
+ t, y = divmod(t, 256)
+ t, z = divmod(t, 256)
+ # Zero is a poor seed, so substitute 1
+ self._seed = (x or 1, y or 1, z or 1)
+
+ def whseed(self, a=None):
+ """Seed from hashable object's hash code.
+
+ None or no argument seeds from current time. It is not guaranteed
+ that objects with distinct hash codes lead to distinct internal
+ states.
+
+ This is obsolete, provided for compatibility with the seed routine
+ used prior to Python 2.1. Use the .seed() method instead.
+ """
+
+ if a is None:
+ self.__whseed()
+ return
+ a = hash(a)
+ a, x = divmod(a, 256)
+ a, y = divmod(a, 256)
+ a, z = divmod(a, 256)
+ x = (x + a) % 256 or 1
+ y = (y + a) % 256 or 1
+ z = (z + a) % 256 or 1
+ self.__whseed(x, y, z)
+
## ---- Methods below this point do not need to be overridden when
## ---- subclassing for the purpose of using a different core generator.
@@ -623,6 +652,7 @@
getstate = _inst.getstate
setstate = _inst.setstate
jumpahead = _inst.jumpahead
+whseed = _inst.whseed
if __name__ == '__main__':
_test()