add comment about \001 and \002'

Author: tanloong

Lib/sqlite3/__main__.py

@@ -132,12 +132,12 @@ def main(*args):
     theme = get_theme()
     s = theme.syntax
 
-    if s.prompt:
-        sys.ps1 = f"\001{s.prompt}\002sqlite> \001{s.reset}\002"
-        sys.ps2 = f"\001{s.prompt}\002    ... \001{s.reset}\002"
-    else:
-        sys.ps1 = f"sqlite> "
-        sys.ps2 = f"    ... "
+    # Use RL_PROMPT_START_IGNORE (\001) and RL_PROMPT_END_IGNORE (\002) to
+    # bracket non-printing characters. This tells readline to ignore them when
+    # calculating screen space for redisplay during history scrolling. See
+    # https://stackoverflow.com/a/9468954 for more details.
+    sys.ps1 = f"\001{s.prompt}\002sqlite> \001{s.reset}\002"
+    sys.ps2 = f"\001{s.prompt}\002    ... \001{s.reset}\002"
 
     con = sqlite3.connect(args.filename, isolation_level=None)
     try: