From 32704bf4ebd680f47cc4ba80ef786ef74fd0d974 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Sat, 2 May 2015 19:33:25 +0300
Subject: [PATCH] Add weakref support for Symbols, fix sympy/sympy#8825

At this commit::

    $ ./bin/isympy -q
    Python console for SymPy 0.7.6-git (Python 2.7.3-64-bit) (ground types: python)

    >>> import weakref
    >>> d = weakref.WeakKeyDictionary([(x,1), (y, 2)])
    >>> print(d.items())
    [(x, 1), (y, 2)]
    >>> del x
    >>> print(d.items())
    [(y, 2)]
---
 sympy/core/symbol.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sympy/core/symbol.py b/sympy/core/symbol.py
index eb8d802e1cc..d8e111ed777 100644
--- a/sympy/core/symbol.py
+++ b/sympy/core/symbol.py
@@ -34,7 +34,7 @@ class Symbol(AtomicExpr, Boolean):
 
     is_comparable = False
 
-    __slots__ = ['name']
+    __slots__ = ['name', '__weakref__']
 
     is_Symbol = True