[Python-checkins] bpo-32554: Deprecate hashing arbitrary types in random.seed() (GH-15382)

[Raymond Hettinger]

https://github.com/python/cpython/commit/d0cdeaab76fef8a6e5a04665df226b6659111e4e
commit: d0cdeaab76fef8a6e5a04665df226b6659111e4e
branch: master
author: Raymond Hettinger <rhettinger at users.noreply.github.com>
committer: GitHub <noreply at github.com>
date: 2019-08-22T09:19:36-07:00
summary:

bpo-32554: Deprecate hashing arbitrary types in random.seed() (GH-15382)

files:
A Misc/NEWS.d/next/Library/2019-08-22-01-49-05.bpo-32554.4xiXyM.rst
M Doc/library/random.rst
M Doc/whatsnew/3.9.rst
M Lib/random.py

diff --git a/Doc/library/random.rst b/Doc/library/random.rst
index 90b86248e6e1..1bd1856937be 100644
--- a/Doc/library/random.rst
+++ b/Doc/library/random.rst
@@ -86,6 +86,11 @@ Bookkeeping functions
    .. versionchanged:: 3.2
       Moved to the version 2 scheme which uses all of the bits in a string seed.
 
+   .. deprecated:: 3.9
+      In the future, the *seed* must be one of the following types:
+      *NoneType*, :class:`int`, :class:`float`, :class:`str`,
+      :class:`bytes`, or :class:`bytearray`.
+
 .. function:: getstate()
 
    Return an object capturing the current internal state of the generator.  This
@@ -316,6 +321,11 @@ Alternative Generator
    Class that implements the default pseudo-random number generator used by the
    :mod:`random` module.
 
+   .. deprecated:: 3.9
+      In the future, the *seed* must be one of the following types:
+      :class:`NoneType`, :class:`int`, :class:`float`, :class:`str`,
+      :class:`bytes`, or :class:`bytearray`.
+
 .. class:: SystemRandom([seed])
 
    Class that uses the :func:`os.urandom` function for generating random numbers
diff --git a/Doc/whatsnew/3.9.rst b/Doc/whatsnew/3.9.rst
index 6615a2e28eff..05a17a5c7390 100644
--- a/Doc/whatsnew/3.9.rst
+++ b/Doc/whatsnew/3.9.rst
@@ -169,6 +169,12 @@ Deprecated
   of Python. For the majority of use cases users can leverage the Abstract Syntax
   Tree (AST) generation and compilation stage, using the :mod:`ast` module.
 
+* The :mod:`random` module currently accepts any hashable type as a
+  possible seed value.  Unfortunately, some of those types are not
+  guaranteed to have a deterministic hash value.  After Python 3.9,
+  the module will restrict its seeds to *None*, :class:`int`,
+  :class:`float`, :class:`str`, :class:`bytes`, and :class:`bytearray`.
+
 
 Removed
 =======
diff --git a/Lib/random.py b/Lib/random.py
index 365a01957203..be4401c554d7 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -121,7 +121,10 @@ def __init_subclass__(cls, /, **kwargs):
                 break
 
     def seed(self, a=None, version=2):
-        """Initialize internal state from hashable object.
+        """Initialize internal state from a seed.
+
+        The only supported seed types are None, int, float,
+        str, bytes, and bytearray.
 
         None or no argument seeds from current time or from an operating
         system specific randomness source if available.
@@ -143,12 +146,20 @@ def seed(self, a=None, version=2):
             x ^= len(a)
             a = -2 if x == -1 else x
 
-        if version == 2 and isinstance(a, (str, bytes, bytearray)):
+        elif version == 2 and isinstance(a, (str, bytes, bytearray)):
             if isinstance(a, str):
                 a = a.encode()
             a += _sha512(a).digest()
             a = int.from_bytes(a, 'big')
 
+        elif not isinstance(a, (type(None), int, float, str, bytes, bytearray)):
+            _warn('Seeding based on hashing is deprecated\n'
+                  'since Python 3.9 and will be removed in a subsequent '
+                  'version. The only \n'
+                  'supported seed types are: None, '
+                  'int, float, str, bytes, and bytearray.',
+                  DeprecationWarning, 2)
+
         super().seed(a)
         self.gauss_next = None
 
diff --git a/Misc/NEWS.d/next/Library/2019-08-22-01-49-05.bpo-32554.4xiXyM.rst b/Misc/NEWS.d/next/Library/2019-08-22-01-49-05.bpo-32554.4xiXyM.rst
new file mode 100644
index 000000000000..752cf48a4543
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-08-22-01-49-05.bpo-32554.4xiXyM.rst
@@ -0,0 +1 @@
+Deprecate having random.seed() call hash on arbitrary types.