- use a different bitwise approach here that doesn't require iterating

through all possible set values

3 files changed, 16 insertions, 6 deletions

diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index 7836e9548..9c3f23cb2 100644
--- a/lib/sqlalchemy/dialects/mysql/base.py
+++ b/lib/sqlalchemy/dialects/mysql/base.py
@@ -1496,6 +1496,10 @@ class SET(_EnumeratedValues):
                 (value, 2 ** idx)
                 for idx, value in enumerate(self.values)
             )
+            self._bitmap.update(
+                (2 ** idx, value)
+                for idx, value in enumerate(self.values)
+            )
         kw.setdefault('length', length)
         super(SET, self).__init__(**kw)
 
@@ -1510,12 +1514,9 @@ class SET(_EnumeratedValues):
             def process(value):
                 if value is not None:
                     value = int(value)
+
                     return set(
-                        [
-                            elem
-                            for idx, elem in enumerate(self.values)
-                            if value & (2 ** idx)
-                        ]
+                        util.map_bits(self._bitmap.__getitem__, value)
                     )
                 else:
                     return None
diff --git a/lib/sqlalchemy/util/__init__.py b/lib/sqlalchemy/util/__init__.py
index dfed5b90a..7c85ef94b 100644
--- a/lib/sqlalchemy/util/__init__.py
+++ b/lib/sqlalchemy/util/__init__.py
@@ -36,7 +36,7 @@ from .langhelpers import iterate_attributes, class_hierarchy, \
     generic_repr, counter, PluginLoader, hybridproperty, hybridmethod, \
     safe_reraise,\
     get_callable_argspec, only_once, attrsetter, ellipses_string, \
-    warn_limited
+    warn_limited, map_bits
 
 from .deprecations import warn_deprecated, warn_pending_deprecation, \
     deprecated, pending_deprecation, inject_docstring_text
diff --git a/lib/sqlalchemy/util/langhelpers.py b/lib/sqlalchemy/util/langhelpers.py
index 7f57e501a..b708665f9 100644
--- a/lib/sqlalchemy/util/langhelpers.py
+++ b/lib/sqlalchemy/util/langhelpers.py
@@ -92,6 +92,15 @@ def _unique_symbols(used, *bases):
             raise NameError("exhausted namespace for symbol base %s" % base)
 
 
+def map_bits(fn, n):
+    """Call the given function given each nonzero bit from n."""
+
+    while n:
+        b = n & (~n + 1)
+        yield fn(b)
+        n ^= b
+
+
 def decorator(target):
     """A signature-matching decorator factory."""