remove instanceof() in favor of memoized flags, part of [ticket:1566]

2 files changed, 28 insertions, 10 deletions

diff --git a/lib/sqlalchemy/schema.py b/lib/sqlalchemy/schema.py
index 845459e81..7965070d1 100644
--- a/lib/sqlalchemy/schema.py
+++ b/lib/sqlalchemy/schema.py
@@ -1043,6 +1043,8 @@ class DefaultGenerator(SchemaItem):
 
     __visit_name__ = 'default_generator'
 
+    is_sequence = False
+    
     def __init__(self, for_update=False):
         self.for_update = for_update
 
@@ -1084,7 +1086,15 @@ class ColumnDefault(DefaultGenerator):
         if util.callable(arg):
             arg = self._maybe_wrap_callable(arg)
         self.arg = arg
-
+    
+    @util.memoized_property
+    def is_callable(self):
+        return util.callable(self.arg)
+        
+    @util.memoized_property
+    def is_clause_element(self):
+        return isinstance(self.arg, expression.ClauseElement)
+        
     def _maybe_wrap_callable(self, fn):
         """Backward compat: Wrap callables that don't accept a context."""
 
@@ -1133,6 +1143,8 @@ class Sequence(DefaultGenerator):
 
     __visit_name__ = 'sequence'
 
+    is_sequence = True
+    
     def __init__(self, name, start=None, increment=None, schema=None,
                  optional=False, quote=None, metadata=None, for_update=False):
         super(Sequence, self).__init__(for_update=for_update)
@@ -1144,6 +1156,14 @@ class Sequence(DefaultGenerator):
         self.schema = schema
         self.metadata = metadata
 
+    @util.memoized_property
+    def is_callable(self):
+        return False
+
+    @util.memoized_property
+    def is_clause_element(self):
+        return False
+
     def __repr__(self):
         return "Sequence(%s)" % ', '.join(
             [repr(self.name)] +
diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 4cf4bd869..61c6c214f 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -823,13 +823,12 @@ class SQLCompiler(engine.Compiled):
                         ):
                         
                         if implicit_returning:
-                            if isinstance(c.default, schema.Sequence):
+                            if c.default is not None and c.default.is_sequence:
                                 proc = self.process(c.default)
                                 if proc is not None:
                                     values.append((c, proc))
                                 self.returning.append(c)
-                            elif isinstance(c.default, schema.ColumnDefault) and \
-                                        isinstance(c.default.arg, sql.ClauseElement):
+                            elif c.default is not None and c.default.is_clause_element:
                                 values.append((c, self.process(c.default.arg.self_group())))
                                 self.returning.append(c)
                             elif c.default is not None:
@@ -842,21 +841,20 @@ class SQLCompiler(engine.Compiled):
                                 c.default is not None and \
                                     (
                                         self.dialect.supports_sequences or 
-                                        not isinstance(c.default, schema.Sequence)
+                                        not c.default.is_sequence
                                     )
                                 ) or self.dialect.preexecute_autoincrement_sequences:
 
                                 values.append((c, self._create_crud_bind_param(c, None)))
                                 self.prefetch.append(c)
 
-                    elif isinstance(c.default, schema.Sequence):
+                    elif c.default is not None and c.default.is_sequence:
                         proc = self.process(c.default)
                         if proc is not None:
                             values.append((c, proc))
                             if not c.primary_key:
                                 self.postfetch.append(c)
-                    elif isinstance(c.default, schema.ColumnDefault) and \
-                            isinstance(c.default.arg, sql.ClauseElement):
+                    elif c.default is not None and c.default.is_clause_element:
                         values.append((c, self.process(c.default.arg.self_group())))
                         
                         if not c.primary_key:
@@ -869,8 +867,8 @@ class SQLCompiler(engine.Compiled):
                         if not c.primary_key:
                             self.postfetch.append(c)
                 elif self.isupdate:
-                    if isinstance(c.onupdate, schema.ColumnDefault):
-                        if isinstance(c.onupdate.arg, sql.ClauseElement):
+                    if c.onupdate is not None and not c.onupdate.is_sequence:
+                        if c.onupdate.is_clause_element:
                             values.append((c, self.process(c.onupdate.arg.self_group())))
                             self.postfetch.append(c)
                         else: