diff --git a/zipline/algorithm.py b/zipline/algorithm.py
index f4f26c02..fca53d4e 100644
--- a/zipline/algorithm.py
+++ b/zipline/algorithm.py
@@ -81,9 +81,8 @@ class TradingAlgorithm(object):
 
     def _create_generator(self, environment):
         """
-        Create trading environment, transforms and SimulatedTrading object.
-
-        Gets called by self.run().
+        Create a basic generator setup using the sources and
+        transforms attached to this algorithm.
         """
 
         self.date_sorted = date_sorted_sources(*self.sources)
@@ -96,6 +95,17 @@ class TradingAlgorithm(object):
 
         return self.trading_client.simulate(self.with_tnfms)
 
+    def get_generator(self, environment):
+        """
+        Override this method to add new logic to the construction
+        of the generator. Overrides can use the _create_generator
+        method to get a standard construction generator.
+        """
+        return self._create_generator(environment)
+
+    # TODO: make a new subclass, e.g. BatchAlgorithm, and move
+    # the run method to the subclass, and refactor to put the
+    # generator creation logic into get_generator.
     def run(self, source, start=None, end=None):
         """Run the algorithm.
 
diff --git a/zipline/finance/performance.py b/zipline/finance/performance.py
index 104caeb0..704383e5 100644
--- a/zipline/finance/performance.py
+++ b/zipline/finance/performance.py
@@ -404,9 +404,12 @@ class PerformancePeriod(object):
         self.ending_value = 0.0
         self.period_capital_used = 0.0
         self.pnl = 0.0
-        assert isinstance(initial_positions, positiondict)
         #sid => position object
-        self.positions = initial_positions
+        if not isinstance(initial_positions, positiondict):
+            self.positions = positiondict()
+            self.positions.update(initial_positions)
+        else:
+            self.positions = initial_positions
         self.starting_value = starting_value
         #cash balance at start of period
         self.starting_cash = starting_cash
@@ -435,8 +438,6 @@ class PerformancePeriod(object):
     def execute_transaction(self, txn):
         # Update Position
         # ----------------
-        #if txn.sid not in self.positions:
-        #    self.positions[txn.sid] = Position(txn.sid)
         self.positions[txn.sid].update(txn)
         self.period_capital_used += -1 * txn.price * txn.amount
 
diff --git a/zipline/gens/tradesimulation.py b/zipline/gens/tradesimulation.py
index b94f3c86..0eb6bf20 100644
--- a/zipline/gens/tradesimulation.py
+++ b/zipline/gens/tradesimulation.py
@@ -147,10 +147,6 @@ class AlgorithmSimulator(object):
         # We want an ndict that will have empty ndicts as default
         # values on missing keys.
         self.universe = ndict(default=ndict)
-        # TODO: these keys are being inserted because universe
-        # has a default dictionary backing __internal.
-        # del self.universe['__members__']
-        # del self.universe['__methods__']
 
         # We don't have a datetime for the current snapshot until we
         # receive a message.
diff --git a/zipline/utils/protocol_utils.py b/zipline/utils/protocol_utils.py
index a37895fe..22f4b19a 100644
--- a/zipline/utils/protocol_utils.py
+++ b/zipline/utils/protocol_utils.py
@@ -47,9 +47,10 @@ class ndict(MutableMapping):
 
     def __init__(self, dct=None, default=None):
         if default is not None:
-            self.__internal = dict()
-        else:
             self.__internal = defaultdict(default)
+        else:
+            self.__internal = dict()
+
         if not ndict.cls:
             ndict.cls = frozenset(dir(self))
 
diff --git a/zipline/utils/simfactory.py b/zipline/utils/simfactory.py
index b9dd78c4..025628eb 100644
--- a/zipline/utils/simfactory.py
+++ b/zipline/utils/simfactory.py
@@ -86,10 +86,11 @@ def create_test_zipline(**config):
             concurrent=concurrent_trades
         )
 
+    test_algo.set_sources([trade_source])
+
     #-------------------
     # Transforms
     #-------------------
-    test_algo.set_sources([trade_source])
 
     transforms = config.get('transforms', None)
     if transforms is not None:
@@ -104,6 +105,6 @@ def create_test_zipline(**config):
 
     # ------------------
     # generator/simulator
-    sim = test_algo._create_generator(trading_environment)
+    sim = test_algo.get_generator(trading_environment)
 
     return sim