#12448: smtplib now flushes stdout while running ``python -m smtplib``
  in order to display the prompt correctly.  Patch by Petri Lehtinen.
diff --git a/Lib/smtplib.py b/Lib/smtplib.py
index 13c56e1..fbef96e 100644
--- a/Lib/smtplib.py
+++ b/Lib/smtplib.py
@@ -912,6 +912,7 @@
 
     def prompt(prompt):
         sys.stdout.write(prompt + ": ")
+        sys.stdout.flush()
         return sys.stdin.readline().strip()
 
     fromaddr = prompt("From")