Try to elide long completion based on user input.

If what the user has typed is already in the completion and the
completion is really long, try to elide what the user has already typed
from the displayed text of the completion.

Keep the first 3 and last 3 of what is already present.

This will behave weirdly if all the completion have a common prefix as I
believe prompt toolkit will insert the common prefix (or do we?). I'll
have to check how to consider the common prefix as being typed.

IPython/core/interactiveshell.py

@@ -2217,7 +2217,7 b' class InteractiveShell(SingletonConfigurable):'
         The position argument (defaults to 0) is the index in the completers
         list where you want the completer to be inserted."""
 
-        newcomp = types.MethodType(completer,self.Completer)
+        newcomp = types.MethodType(completer, self.Completer)
         self.Completer.custom_matchers.insert(pos,newcomp)
 
     def set_completer_frame(self, frame=None):

IPython/terminal/ptutils.py

@@ -23,7 +23,7 b' import os'
 
 _completion_sentinel = object()
 
-def _elide(string, *, min_elide=30):
+def _elide_point(string, *, min_elide=30):
     """
     If a string is long enough, and has at least 3 dots,
     replace the middle part with ellipses.
@@ -53,6 +53,24 b' def _elide(string, *, min_elide=30):'
 
     return string
 
+def _elide_typed(string, typed, *, min_elide=30):
+    """
+    Elide the middle of a long string if the beginning has already been typed.
+    """
+
+    if len(string) < min_elide:
+        return string
+    cut_how_much = len(typed)-3
+    if string.startswith(typed) and len(string)> len(typed):
+        return f"{string[:3]}\N{HORIZONTAL ELLIPSIS}{string[cut_how_much:]}"
+    return string
+
+def _elide(string, typed, min_elide=30):
+    return _elide_typed(
+        _elide_point(string, min_elide=min_elide),
+        typed, min_elide=min_elide)
+
+
 
 def _adjust_completion_text_based_on_context(text, body, offset):
     if text.endswith('=') and len(body) > offset and body[offset] == '=':
@@ -89,7 +107,11 b' class IPythonPTCompleter(Completer):'
             cursor_col = document.cursor_position_col
             cursor_position = document.cursor_position
             offset = cursor_to_position(body, cursor_row, cursor_col)
-            yield from self._get_completions(body, offset, cursor_position, self.ipy_completer)
+            try:
+                yield from self._get_completions(body, offset, cursor_position, self.ipy_completer)
+            except Exception as e:
+                from traceback import print_tb
+                print_tb(e)
 
     @staticmethod
     def _get_completions(body, offset, cursor_position, ipyc):
@@ -128,9 +150,9 b' class IPythonPTCompleter(Completer):'
 
             adjusted_text = _adjust_completion_text_based_on_context(c.text, body, offset)
             if c.type == 'function':
-                yield Completion(adjusted_text, start_position=c.start - offset, display=_elide(display_text+'()'), display_meta=c.type+c.signature)
+                yield Completion(adjusted_text, start_position=c.start - offset, display=_elide(display_text+'()', body[c.start:c.end]), display_meta=c.type+c.signature)
             else:
-                yield Completion(adjusted_text, start_position=c.start - offset, display=_elide(display_text), display_meta=c.type)
+                yield Completion(adjusted_text, start_position=c.start - offset, display=_elide(display_text,  body[c.start:c.end]), display_meta=c.type)
 
 class IPythonPTLexer(Lexer):
     """