add an cache.underscore_memoization decorator to make some recurring patterns easier to read

jedi/cache.py

@@ -102,6 +102,37 @@ def cache_call_signatures(stmt):
     return None if module_path is None else (module_path, stmt.start_pos)
 
 
+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.
+    """
+    def wrapper(self):
+        name = '_' + func.__name__
+        try:
+            return getattr(self, name)
+        except AttributeError:
+            result = func(self)
+            setattr(self, name, result)
+            return result
+
+    return wrapper
+
+
 def cache_star_import(func):
     def wrapper(evaluator, scope, *args, **kwargs):
         with common.ignored(KeyError):

jedi/modules.py

@@ -67,23 +67,20 @@ class ModuleWithCursor(object):
         self.position = position
         self._path_until_cursor = None
         self._line_cache = None
-        self._parser = None
 
         # this two are only used, because there is no nonlocal in Python 2
         self._line_temp = None
         self._relevant_temp = None
 
     @property
+    @cache.underscore_memoization
     def parser(self):
         """ get the parser lazy """
-        if not self._parser:
         cache.invalidate_star_import_cache(self.path)
-            self._parser = fast.FastParser(self.source, self.path, self.position)
-            # don't pickle that module, because the main module is changing
-            # quickly usually.
-            cache.save_parser(self.path, self.name, self._parser,
-                              pickling=False)
-        return self._parser
+        parser = fast.FastParser(self.source, self.path, self.position)
+        # Don't pickle that module, because the main module is changing quickly
+        cache.save_parser(self.path, self.name, parser, pickling=False)
+        return parser
 
     def get_path_until_cursor(self):
         """ Get the path under the cursor. """