# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1384628655 -3600
# Node ID 80441a32ce4110deec47d04af04581ae336a441d
# Parent  05ca9a5f6cb2c335cbc9310357e6a7f9e7fdbcdf
Avoid production of context and value lists where only one result is needed.

diff -r 05ca9a5f6cb2 -r 80441a32ce41 micropython/data.py
--- a/micropython/data.py	Sat Nov 16 15:53:25 2013 +0100
+++ b/micropython/data.py	Sat Nov 16 20:04:15 2013 +0100
@@ -388,6 +388,12 @@
 
 # Program data structures.
 
+def only(s):
+    if len(s) == 1:
+        for i in s:
+            return i
+    return None
+
 class BaseAttr:
 
     "A basic attribute entry."
@@ -418,8 +424,9 @@
 
         "Get the context referenced by the attribute."
 
-        if self.get_assignments() == 1 and len(self.get_context_values()) == 1:
-            return self.get_contexts()[0]
+        if self.get_assignments() == 1:
+            context_value = only(self.get_context_values())
+            return context_value and context_value[0]
         else:
             return None
 
@@ -427,8 +434,9 @@
 
         "Get the value referenced by the attribute."
 
-        if self.get_assignments() == 1 and len(self.get_context_values()) == 1:
-            return self.get_values()[0]
+        if self.get_assignments() == 1:
+            context_value = only(self.get_context_values())
+            return context_value and context_value[1]
         else:
             return None