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Issue #29023: Clarify that ints and longs are always deterministic seeds for random.

This commit is contained in:
Raymond Hettinger 2017-01-06 16:13:37 -08:00
parent 9220111fc5
commit 9b7ae96b98
2 changed files with 13 additions and 11 deletions
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18
Doc/library/random.rst
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@ -71,17 +71,17 @@ from sources provided by the operating system.
Bookkeeping functions: Bookkeeping functions:
.. function:: seed([x]) .. function:: seed(a=None)
Initialize the basic random number generator. Optional argument *x* can be any Initialize internal state of the random number generator.
:term:`hashable` object. If *x* is omitted or ``None``, current system time is used;
current system time is also used to initialize the generator when the module is
first imported. If randomness sources are provided by the operating system,
they are used instead of the system time (see the :func:`os.urandom` function
for details on availability).
If a :term:`hashable` object is given, deterministic results are only assured ``None`` or no argument seeds from current time or from an operating
when :envvar:`PYTHONHASHSEED` is disabled. system specific randomness source if available (see the :func:`os.urandom`
function for details on availability).
If *a* is not ``None`` or an :class:`int` or a :class:`long`, then
``hash(a)`` is used instead. Note that the hash values for some types
are nondeterministic when :envvar:`PYTHONHASHSEED` is enabled.
.. versionchanged:: 2.4 .. versionchanged:: 2.4
formerly, operating system resources were not used. formerly, operating system resources were not used.

6
Lib/random.py
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@ -98,12 +98,14 @@ class Random(_random.Random):
self.gauss_next = None self.gauss_next = None
def seed(self, a=None): def seed(self, a=None):
"""Initialize internal state from hashable object. """Initialize internal state of the random number generator.
None or no argument seeds from current time or from an operating None or no argument seeds from current time or from an operating
system specific randomness source if available. system specific randomness source if available.
If a is not None or an int or long, hash(a) is used instead. If a is not None or is an int or long, hash(a) is used instead.
Hash values for some types are nondeterministic when the
PYTHONHASHSEED environment variable is enabled.
""" """
if a is None: if a is None: