MAINT: Reworked Term atomicity

tests/pipeline/test_term.py

@@ -86,10 +86,8 @@ class DependencyResolutionTestCase(TestCase):
         seen = set()
 
         for term in ordered_terms:
-            if not term.atomic:
-                for input_ in term.inputs:
-                    self.assertIn(input_, seen)
-                self.assertIn(term.mask, seen)
+            for dep in term.dependencies:
+                self.assertIn(dep, seen)
 
             seen.add(term)
 

zipline/pipeline/data/dataset.py

@@ -7,7 +7,7 @@ from six import (
     with_metaclass,
 )
 
-from zipline.pipeline.term import AtomicTerm
+from zipline.pipeline.term import Term, AssetExists
 from zipline.pipeline.factors import Latest
 
 
@@ -26,10 +26,13 @@ class Column(object):
         return BoundColumn(dtype=self.dtype, dataset=dataset, name=name)
 
 
-class BoundColumn(AtomicTerm):
+class BoundColumn(Term):
     """
     A Column of data that's been concretely bound to a particular dataset.
     """
+    mask = AssetExists()
+    extra_input_rows = 0
+    inputs = ()
 
     def __new__(cls, dtype, dataset, name):
         return super(BoundColumn, cls).__new__(

zipline/pipeline/engine.py

@@ -236,7 +236,7 @@ class SimplePipelineEngine(object):
         """
         Load mask and mask row labels for term.
         """
-        mask = term.mask if not term.atomic else self._root_mask_term
+        mask = term.mask
         offset = graph.extra_rows[mask] - graph.extra_rows[term]
         return workspace[mask][offset:], dates[offset:]
 

zipline/pipeline/graph.py

@@ -102,16 +102,9 @@ class TermGraph(DiGraph):
         zipline.pipeline.engine.SimplePipelineEngine._inputs_for_term
         zipline.pipeline.engine.SimplePipelineEngine._mask_and_dates_for_term
         """
-        out = {}
-        for term in self:
-            if not term.atomic:
-                extra_input_rows = term.extra_input_rows
-                for input_ in term.inputs:
-                    out[term, input_] = (self.extra_rows[input_]
-                                         - extra_input_rows)
-                mask = term.mask
-                out[term, mask] = self.extra_rows[mask] - extra_input_rows
-        return out
+        return {(term, dep): self.extra_rows[dep] - term.extra_input_rows
+                for term in self
+                for dep in term.dependencies}
 
     @lazyval
     def extra_rows(self):
@@ -192,25 +185,17 @@ class TermGraph(DiGraph):
         # Make sure we're going to compute at least `extra_rows` of `term`.
         self._ensure_extra_rows(term, extra_rows)
 
-        if not term.atomic:
-            # Number of extra rows we need to compute for this term's
-            # dependencies.
-            dependency_extra_rows = extra_rows + term.extra_input_rows
+        # Number of extra rows we need to compute for this term's dependencies.
+        dependency_extra_rows = extra_rows + term.extra_input_rows
 
-            # Recursively add dependencies.
-            for dependency in term.inputs:
-                self._add_to_graph(
-                    dependency,
-                    parents,
-                    extra_rows=dependency_extra_rows,
-                )
-                self.add_edge(dependency, term)
-
-            # Add term's mask, which is really just a specially-enumerated
-            # input.
-            mask = term.mask
-            self._add_to_graph(mask, parents, extra_rows=dependency_extra_rows)
-            self.add_edge(mask, term)
+        # Recursively add dependencies.
+        for dependency in term.dependencies:
+            self._add_to_graph(
+                dependency,
+                parents,
+                extra_rows=dependency_extra_rows,
+            )
+            self.add_edge(dependency, term)
 
         parents.remove(term)
 

zipline/pipeline/term.py

@@ -1,9 +1,11 @@
 """
 Base class for Filters, Factors and Classifiers
 """
+from abc import ABCMeta, abstractproperty
 from weakref import WeakValueDictionary
 
 from numpy import bool_, full, nan
+from six import with_metaclass
 
 from zipline.errors import (
     DTypeNotSpecified,
@@ -38,7 +40,7 @@ class NotSpecified(object):
         return self
 
 
-class Term(object):
+class Term(with_metaclass(ABCMeta, object)):
     """
     Base class for terms in a Pipeline API compute graph.
     """
@@ -135,15 +137,55 @@ class Term(object):
         if self.dtype is NotSpecified:
             raise DTypeNotSpecified(termname=type(self).__name__)
 
-    @property
-    def atomic(self):
+    @abstractproperty
+    def inputs(self):
         """
-        Whether or not this term has dependencies.
-
-        If term.atomic is truthy, it should have dataset and dtype attributes.
+        A tuple of other Terms that this Term requires for computation.
         """
         raise NotImplementedError()
 
+    @abstractproperty
+    def mask(self):
+        """
+        A 2D Filter representing asset/date pairs to include while
+        computing this Term. (True means include; False means exclude.)
+        """
+        raise NotImplementedError()
+
+    @lazyval
+    def dependencies(self):
+        return self.inputs + (self.mask,)
+
+    @lazyval
+    def atomic(self):
+        return not any(dep for dep in self.dependencies
+                       if dep is not AssetExists())
+
+
+class AssetExists(Term):
+    """
+    Pseudo-filter describing whether or not an asset existed on a given day.
+    This is the default mask for all terms that haven't been passed a mask
+    explicitly.
+
+    This is morally a Filter, in the sense that it produces a boolean value for
+    every asset on every date.  We don't subclass Filter, however, because
+    `AssetExists` is computed directly by the PipelineEngine.
+
+    See Also
+    --------
+    zipline.assets.AssetFinder.lifetimes
+    """
+    dtype = bool_
+    dataset = None
+    extra_input_rows = 0
+    inputs = ()
+    dependencies = ()
+    mask = None
+
+    def __repr__(self):
+        return "AssetExists()"
+
 
 # TODO: Move mixins to a separate file?
 class SingleInputMixin(object):
@@ -220,17 +262,6 @@ class CustomTermMixin(object):
         return out
 
 
-class AtomicTerm(Term):
-
-    @property
-    def atomic(self):
-        return True
-
-    @property
-    def dataset(self):
-        raise NotImplementedError()
-
-
 class CompositeTerm(Term):
     inputs = NotSpecified
     window_length = NotSpecified
@@ -295,10 +326,6 @@ class CompositeTerm(Term):
 
         return super(CompositeTerm, self)._validate()
 
-    @property
-    def atomic(self):
-        return False
-
     def _compute(self, inputs, dates, assets, mask):
         """
         Subclasses should implement this to perform actual computation.
@@ -339,31 +366,3 @@ class CompositeTerm(Term):
             inputs=self.inputs,
             window_length=self.window_length,
         )
-
-
-class AssetExists(AtomicTerm):
-    """
-    Pseudo-filter describing whether or not an asset existed on a given day.
-    This is the default mask for all terms that haven't been passed a mask
-    explicitly.
-
-    This is morally a Filter, in the sense that it produces a boolean value for
-    every asset on every date.  We don't subclass Filter, however, because
-    `AssetExists` is computed directly by the PipelineEngine.
-
-    See Also
-    --------
-    zipline.assets.AssetFinder.lifetimes
-    """
-    dtype = bool_
-    dataset = None
-
-    def _compute(self, *args, **kwargs):
-        # TODO: Consider moving the bulk of the logic from
-        # SimplePipelineEngine._compute_root_mask here.
-        raise NotImplementedError(
-            "Direct computation of AssetExists is not supported!"
-        )
-
-    def __repr__(self):
-        return "AssetExists()"