Prevent completion on keys with garbage in it

IPython/core/completer.py

@@ -780,14 +780,20 b' def match_dict_keys(keys: List[Union[str, bytes, Tuple[Union[str, bytes]]]], pre'
     """
     prefix_tuple = extra_prefix if extra_prefix else ()
     Nprefix = len(prefix_tuple)
-    def filter_by_prefix_tuple(key):
+    def filter_prefix_tuple(key):
+        # Reject too short keys
         if len(key) <= Nprefix:
             return False
+        # Reject keys with non str/bytes in it
+        for k in key:
+            if not isinstance(k, (str, bytes)):
+                return False
+        # Reject keys that do not match the prefix
         for k, pt in zip(key, prefix_tuple):
             if k != pt:
                 return False
-        else:
-            return True
+        # All checks passed!
+        return True
 
     filtered_keys:List[Union[str,bytes]] = []
     def _add_to_filtered_keys(key):
@@ -796,7 +802,7 b' def match_dict_keys(keys: List[Union[str, bytes, Tuple[Union[str, bytes]]]], pre'
 
     for k in keys:
         if isinstance(k, tuple):
-            if filter_by_prefix_tuple(k):
+            if filter_prefix_tuple(k):
                 _add_to_filtered_keys(k[Nprefix])
         else:
             _add_to_filtered_keys(k)

IPython/core/tests/test_completer.py

@@ -920,12 +920,16 b' class TestCompleter(unittest.TestCase):'
             "bad": None,
             object(): None,
             5: None,
+            ("abe", None): None,
+            (None, "abf"): None
         }
 
         _, matches = complete(line_buffer="d['a")
         nt.assert_in("abc", matches)
         nt.assert_in("abd", matches)
         nt.assert_not_in("bad", matches)
+        nt.assert_not_in("abe", matches)
+        nt.assert_not_in("abf", matches)
         assert not any(m.endswith(("]", '"', "'")) for m in matches), matches
 
         # check escaping and whitespace