bpo-30419: DOC: Update missing information in bdb docs (#1687)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Co-authored-by: Martin Panter <vadmium@users.noreply.github.com>
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

1 files changed, 10 insertions, 7 deletions

diff --git a/Lib/bdb.py b/Lib/bdb.py
index 75d6113..81fbb85 100644
--- a/Lib/bdb.py
+++ b/Lib/bdb.py
@@ -805,15 +805,18 @@ def checkfuncname(b, frame):
     return True
 
 
-# Determines if there is an effective (active) breakpoint at this
-# line of code.  Returns breakpoint number or 0 if none
 def effective(file, line, frame):
-    """Determine which breakpoint for this file:line is to be acted upon.
+    """Return (active breakpoint, delete temporary flag) or (None, None) as
+       breakpoint to act upon.
 
-    Called only if we know there is a breakpoint at this location.  Return
-    the breakpoint that was triggered and a boolean that indicates if it is
-    ok to delete a temporary breakpoint.  Return (None, None) if there is no
-    matching breakpoint.
+       The "active breakpoint" is the first entry in bplist[line, file] (which
+       must exist) that is enabled, for which checkfuncname is True, and that
+       has neither a False condition nor a positive ignore count.  The flag,
+       meaning that a temporary breakpoint should be deleted, is False only
+       when the condiion cannot be evaluated (in which case, ignore count is
+       ignored).
+
+       If no such entry exists, then (None, None) is returned.
     """
     possibles = Breakpoint.bplist[file, line]
     for b in possibles: