Improved field composition.

backtester/datahandler/schema.py

@@ -53,26 +53,55 @@ class Field:
         self.name = name
         self.mapping = mapping
 
-    def _create_filter(self, op, value):
-        query = Field._format_query(self.mapping, op, value)
+    def _create_filter(self, op, other):
+        if isinstance(other, Field):
+            query = Field._format_query(self.mapping, op, other.mapping)
+        else:
+            query = Field._format_query(self.mapping, op, other)
         return Filter(query)
 
-    def _combine_fields(self, op, other):
-        name = Field._format_query(self.name, op, other.name)
-        mapping = Field._format_query(self.mapping, op, other.mapping)
+    def _combine_fields(self, op, other, invert=False):
+        if isinstance(other, Field):
+            name = Field._format_query(self.name, op, other.name, invert)
+            mapping = Field._format_query(self.mapping, op, other.mapping,
+                                          invert)
+        elif isinstance(other, (int, float)):
+            name = Field._format_query(self.name, op, other, invert)
+            mapping = Field._format_query(self.mapping, op, other, invert)
+        else:
+            raise TypeError
+
         return Field(name, mapping)
 
-    def _format_query(left, op, right):
+    def _format_query(left, op, right, invert=False):
+        if invert:
+            left, right = right, left
         query = "{left} {op} {right}".format(left=left, op=op, right=right)
         return query
 
-    def __add__(self, field):
-        assert isinstance(field, Field)
-        return self._combine_fields("+", field)
+    def __add__(self, value):
+        return self._combine_fields("+", value)
 
-    def __sub__(self, field):
-        assert isinstance(field, Field)
-        return self._create_filter("-", field)
+    def __radd__(self, value):
+        return self._combine_fields("+", value, invert=True)
+
+    def __sub__(self, value):
+        return self._combine_fields("-", value)
+
+    def __rsub__(self, value):
+        return self._combine_fields("-", value, invert=True)
+
+    def __mul__(self, value):
+        return self._combine_fields("*", value)
+
+    def __rmul__(self, value):
+        return self._combine_fields("*", value, invert=True)
+
+    def __truediv__(self, value):
+        return self._combine_fields("/", value)
+
+    def __rtruediv__(self, value):
+        return self._combine_fields("/", value, invert=True)
 
     def __lt__(self, value):
         return self._create_filter("<", value)