Move underscore memoization.

jedi/cache.py

@@ -12,14 +12,48 @@ there are global variables, which are holding the cache information. Some of
 these variables are being cleaned after every API usage.
 """
 import time
+import inspect
 
 from jedi import settings
 from jedi.parser.utils import parser_cache
-from jedi.parser.utils import underscore_memoization
 
 _time_caches = {}
 
 
+def underscore_memoization(func):
+    """
+    Decorator for methods::
+
+        class A(object):
+            def x(self):
+                if self._x:
+                    self._x = 10
+                return self._x
+
+    Becomes::
+
+        class A(object):
+            @underscore_memoization
+            def x(self):
+                return 10
+
+    A now has an attribute ``_x`` written by this decorator.
+    """
+    name = '_' + func.__name__
+
+    def wrapper(self):
+        try:
+            return getattr(self, name)
+        except AttributeError:
+            result = func(self)
+            if inspect.isgenerator(result):
+                result = list(result)
+            setattr(self, name, result)
+            return result
+
+    return wrapper
+
+
 def clear_time_caches(delete_all=False):
     """ Jedi caches many things, that should be completed after each completion
     finishes.