diff --git a/tests/pipeline/test_classifier.py b/tests/pipeline/test_classifier.py
index 8eddb6f8..a716c19d 100644
--- a/tests/pipeline/test_classifier.py
+++ b/tests/pipeline/test_classifier.py
@@ -520,7 +520,7 @@ class TestPostProcessAndToWorkSpaceValue(ZiplineTestCase):
             missing_value = -1
 
         f = F()
-        column_data =np.array(
+        column_data = np.array(
             [[0, f.missing_value],
              [1, f.missing_value],
              [2, 3]],
diff --git a/tests/pipeline/test_engine.py b/tests/pipeline/test_engine.py
index f285af24..a04d663c 100644
--- a/tests/pipeline/test_engine.py
+++ b/tests/pipeline/test_engine.py
@@ -34,7 +34,7 @@ from pandas import (
 from pandas.compat.chainmap import ChainMap
 from pandas.util.testing import assert_frame_equal
 from six import iteritems, itervalues
-from toolz import merge, assoc
+from toolz import merge
 
 from zipline.assets.synthetic import make_rotating_equity_info
 from zipline.errors import NoFurtherDataError
diff --git a/zipline/pipeline/engine.py b/zipline/pipeline/engine.py
index 6c44703e..1d28a834 100644
--- a/zipline/pipeline/engine.py
+++ b/zipline/pipeline/engine.py
@@ -81,11 +81,36 @@ class ExplodingPipelineEngine(PipelineEngine):
         )
 
 
-def _default_populate_initial_workspace(initial_workspace,
-                                        root_mask_term,
-                                        execution_plan,
-                                        dates,
-                                        assets):
+def default_populate_initial_workspace(initial_workspace,
+                                       root_mask_term,
+                                       execution_plan,
+                                       dates,
+                                       assets):
+    """The default implementation for ``populate_initial_workspace``. This
+    function returns the ``initial_workspace`` argument without making any
+    modifications.
+
+    Parameters
+    ----------
+    initial_workspace : dict[array-like]
+        The initial workspace before we have populated it with any cached
+        terms.
+    root_mask_term : Term
+        The root mask term, normally ``AssetExists()``. This is needed to
+        compute the dates for individual terms.
+    execution_plan : ExecutionPlan
+        The execution plan for the pipeline being run.
+    dates : pd.DatetimeIndex
+        All of the dates being requested in this pipeline run including
+        the extra dates for look back windows.
+    assets : pd.Int64Index
+        All of the assets that exist for the window being computed.
+
+    Returns
+    -------
+    populated_initial_workspace : dict[term, array-like]
+        The workspace to begin computations with.
+    """
     return initial_workspace
 
 
@@ -106,10 +131,13 @@ class SimplePipelineEngine(object):
         which assets are in the top-level universe at any point in time.
     populate_initial_workspace : callable, optional
         A function which will be used to populate the initial workspace when
-        computing a pipeline. This function will be passed the
-        initial_workspace, the root mask term, the execution_plan, the dates
-        being computed for, and the assets requested and should return a new
-        dictionary which will be used as the initial_workspace.
+        computing a pipeline. See
+        :func:`zipline.pipeline.engine.default_populate_initial_workspace`
+        for more info.
+
+    See Also
+    --------
+    :func:`zipline.pipeline.engine.default_populate_initial_workspace`
     """
     __slots__ = (
         '_get_loader',
@@ -134,7 +162,7 @@ class SimplePipelineEngine(object):
         self._root_mask_dates_term = InputDates()
 
         self._populate_initial_workspace = (
-            populate_initial_workspace or _default_populate_initial_workspace
+            populate_initial_workspace or default_populate_initial_workspace
         )
 
     def run_pipeline(self, pipeline, start_date, end_date):
diff --git a/zipline/pipeline/graph.py b/zipline/pipeline/graph.py
index f4a8cc2c..89107f03 100644
--- a/zipline/pipeline/graph.py
+++ b/zipline/pipeline/graph.py
@@ -195,9 +195,6 @@ class TermGraph(object):
                 garbage.add(parent)
         return garbage
 
-    def __iter__(self):
-        return iter(self.graph)
-
 
 class ExecutionPlan(TermGraph):
     """
diff --git a/zipline/testing/predicates.py b/zipline/testing/predicates.py
index 7a6989b6..cf4f042e 100644
--- a/zipline/testing/predicates.py
+++ b/zipline/testing/predicates.py
@@ -492,7 +492,6 @@ assert_index_equal = _register_assert_equal_wrapper(
 )
 
 
-
 @assert_equal.register(pd.Categorical, pd.Categorical)
 def assert_categorical_equal(result, expected, path=(), msg='', **kwargs):
     assert_equal(