From 88eeb3689d59c072686df3c17ad0e0884980249a Mon Sep 17 00:00:00 2001
From: Scott Sanderson <ssanderson@quantopian.com>
Date: Wed, 6 Apr 2016 13:25:56 -0400
Subject: [PATCH] MAINT: Make dependencies a dict.

---
 zipline/pipeline/data/dataset.py |  1 -
 zipline/pipeline/graph.py        | 35 ++++++++------------------------
 zipline/pipeline/term.py         | 25 +++++++++++++++--------
 3 files changed, 24 insertions(+), 37 deletions(-)

diff --git a/zipline/pipeline/data/dataset.py b/zipline/pipeline/data/dataset.py
index da236541..b5980d83 100644
--- a/zipline/pipeline/data/dataset.py
+++ b/zipline/pipeline/data/dataset.py
@@ -114,7 +114,6 @@ class BoundColumn(LoadableTerm):
         The name of this column.
     """
     mask = AssetExists()
-    extra_input_rows = 0
     inputs = ()
 
     def __new__(cls, dtype, missing_value, dataset, name):
diff --git a/zipline/pipeline/graph.py b/zipline/pipeline/graph.py
index 5f815065..6290c937 100644
--- a/zipline/pipeline/graph.py
+++ b/zipline/pipeline/graph.py
@@ -104,9 +104,9 @@ class TermGraph(DiGraph):
         zipline.pipeline.engine.SimplePipelineEngine._inputs_for_term
         zipline.pipeline.engine.SimplePipelineEngine._mask_and_dates_for_term
         """
-        return {(term, dep): self.extra_rows[dep] - term.extra_input_rows
+        return {(term, dep): self.extra_rows[dep] - additional_extra_rows
                 for term in self
-                for dep in term.dependencies}
+                for dep, additional_extra_rows in term.dependencies.items()}
 
     @lazyval
     def extra_rows(self):
@@ -119,10 +119,9 @@ class TermGraph(DiGraph):
         Notes
         ----
         This value depends on the other terms in the graph that require `term`
-        **as an input**.  This is not to be confused with
-        `term.extra_input_rows`, which is how many extra rows of `term`'s
-        inputs we need to load, and which is determined entirely by `Term`
-        itself.
+        **as an input**.  This is not to be confused with `term.dependencies`,
+        which describes how many additional rows of `term`'s inputs we need to
+        load, and which is determined entirely by `Term` itself.
 
         Example
         -------
@@ -144,7 +143,7 @@ class TermGraph(DiGraph):
         See Also
         --------
         zipline.pipeline.graph.TermGraph.offset
-        zipline.pipeline.term.Term.extra_input_rows
+        zipline.pipeline.term.Term.dependencies
         """
         return {
             term: attrs['extra_rows']
@@ -187,30 +186,12 @@ class TermGraph(DiGraph):
         # Make sure we're going to compute at least `extra_rows` of `term`.
         self._ensure_extra_rows(term, extra_rows)
 
-        # Number of extra rows we need to compute for this term's dependencies.
-        dependency_extra_rows = extra_rows + term.extra_input_rows
-
-        if isinstance(term, ComputableTerm):
-            # For computable terms, we want to manually add the term's mask to
-            # the graph with zero extra rows. A computable term does not
-            # directly require its mask to have any extra rows. Only loadable
-            # terms should dictate how many extra rows a mask should compute.
-            self._add_to_graph(
-                term.mask,
-                parents,
-                extra_rows=0,
-            )
-            self.add_edge(term.mask, term)
-            dependencies = term.inputs
-        else:
-            dependencies = term.dependencies
-
         # Recursively add dependencies.
-        for dependency in dependencies:
+        for dependency, additional_extra_rows in term.dependencies.items():
             self._add_to_graph(
                 dependency,
                 parents,
-                extra_rows=dependency_extra_rows,
+                extra_rows=extra_rows + additional_extra_rows,
             )
             self.add_edge(dependency, term)
 
diff --git a/zipline/pipeline/term.py b/zipline/pipeline/term.py
index 07b0ef8f..16faf227 100644
--- a/zipline/pipeline/term.py
+++ b/zipline/pipeline/term.py
@@ -294,13 +294,13 @@ class Term(with_metaclass(ABCMeta, object)):
         """
         raise NotImplementedError('mask')
 
-    @lazyval
+    @abstractproperty
     def dependencies(self):
         """
-        A tuple containing all terms that must be computed before this term can
-        be loaded or computed.
+        A dictionary mapping terms that must be computed before `self` to the
+        number of extra rows needed for those terms.
         """
-        return self.inputs + (self.mask,)
+        raise NotImplementedError('dependencies')
 
 
 class AssetExists(Term):
@@ -319,9 +319,8 @@ class AssetExists(Term):
     """
     dtype = bool_dtype
     dataset = None
-    extra_input_rows = 0
     inputs = ()
-    dependencies = ()
+    dependencies = {}
     mask = None
     windowed = False
 
@@ -335,9 +334,12 @@ class LoadableTerm(Term):
 
     This is the base class for :class:`zipline.pipeline.data.BoundColumn`.
     """
-    inputs = ()
     windowed = False
 
+    @lazyval
+    def dependencies(self):
+        return {self.mask: 0}
+
 
 class ComputableTerm(Term):
     """
@@ -442,12 +444,17 @@ class ComputableTerm(Term):
         )
 
     @lazyval
-    def extra_input_rows(self):
+    def dependencies(self):
         """
         The number of extra rows needed for each of our inputs to compute this
         term.
         """
-        return max(0, self.window_length - 1)
+        extra_input_rows = max(0, self.window_length - 1)
+        out = {}
+        for term in self.inputs:
+            out[term] = extra_input_rows
+        out[self.mask] = 0
+        return out
 
     def __repr__(self):
         return (