Add IS (NOT) DISTINCT FROM operators

None / True / False render as literals.
For SQLite, "IS" is used as SQLite lacks
"IS DISTINCT FROM" but its "IS" operator acts
this way for NULL.

Doctext-author: Mike Bayer <mike_mp@zzzcomputing.com>
Change-Id: I9227b81f7207b42627a0349d14d40b46aa756cce
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/248

1 files changed, 33 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/operators.py b/lib/sqlalchemy/sql/operators.py
index 80f08a97c..bf470710d 100644
--- a/lib/sqlalchemy/sql/operators.py
+++ b/lib/sqlalchemy/sql/operators.py
@@ -311,6 +311,28 @@ class ColumnOperators(Operators):
         """
         return self.operate(ne, other)
 
+    def is_distinct_from(self, other):
+        """Implement the ``IS DISTINCT FROM`` operator.
+
+        Renders "a IS DISTINCT FROM b" on most platforms;
+        on some such as SQLite may render "a IS NOT b".
+
+        .. versionadded:: 1.1
+
+        """
+        return self.operate(is_distinct_from, other)
+
+    def isnot_distinct_from(self, other):
+        """Implement the ``IS NOT DISTINCT FROM`` operator.
+
+        Renders "a IS NOT DISTINCT FROM b" on most platforms;
+        on some such as SQLite may render "a IS b".
+
+        .. versionadded:: 1.1
+
+        """
+        return self.operate(isnot_distinct_from, other)
+
     def __gt__(self, other):
         """Implement the ``>`` operator.
 
@@ -722,6 +744,15 @@ def istrue(a):
 def isfalse(a):
     raise NotImplementedError()
 
+
+def is_distinct_from(a, b):
+    return a.is_distinct_from(b)
+
+
+def isnot_distinct_from(a, b):
+    return a.isnot_distinct_from(b)
+
+
 def is_(a, b):
     return a.is_(b)
 
@@ -931,6 +962,8 @@ _PRECEDENCE = {
 
     eq: 5,
     ne: 5,
+    is_distinct_from: 5,
+    isnot_distinct_from: 5,
     gt: 5,
     lt: 5,
     ge: 5,