Get jedi completions on only text before the cursor

Closes gh-10781

This might make completions less smart in some situations, if Jedi can
do intelligent things with the text after the cursor, but it fixes an
important case that has been causing annoyances.

IPython/core/completer.py

@@ -1340,7 +1340,6 b' class IPCompleter(Completer):'
             namespaces.append(self.global_namespace)
 
         completion_filter = lambda x:x
-        # cursor_pos is an it, jedi wants line and column
         offset = cursor_to_position(text, cursor_line, cursor_column)
         # filter output if we are completing for object members
         if offset:
@@ -1356,7 +1355,7 b' class IPCompleter(Completer):'
                     raise ValueError("Don't understand self.omit__names == {}".format(self.omit__names))
 
         interpreter = jedi.Interpreter(
-            text, namespaces, column=cursor_column, line=cursor_line + 1)
+            text[:offset], namespaces, column=cursor_column, line=cursor_line + 1)
         try_jedi = True
 
         try: