Avoid regeneration of candidates. Store them when state is 0 and returns

them one by one on subsequent calls

http://tiswww.case.edu/php/chet/readline/readline.html#How-Completing-Works

> *state* is zero the first time the function is called, allowing the
> generator to perform any necessary initialization, and a positive
> non-zero integer for each subsequent call. Usually the generator
> function computes the list of possible completions when *state* is zero,
> and returns them one at a time on subsequent calls.

Author: tanloong

Lib/sqlite3/_completer.py

@@ -27,11 +27,14 @@
             "UPDATE", "USING", "VACUUM", "VALUES", "VIEW", "VIRTUAL",
             "WHEN", "WHERE", "WINDOW", "WITH", "WITHOUT"]
 
+_completion_matches = ()
 
 def _complete(text, state):
-    options = [c + " " for c in _keywords if c.startswith(text.upper())]
+    global _completion_matches
+    if state == 0:
+        _completion_matches = tuple(c + " " for c in _keywords if c.startswith(text.upper()))
     try:
-        return options[state]
+        return _completion_matches[state]
     except IndexError:
         return None