smtplib: add ability to bind to specific source IP address/port

Lib/smtplib.py

 #! /usr/bin/env python3
 
 '''SMTP/ESMTP client class.
 
 This should follow RFC 821 (SMTP), RFC 1869 (ESMTP), RFC 2554 (SMTP
 Authentication) and RFC 2487 (Secure SMTP over TLS).
 
 Notes:
 
 Please remember, when doing ESMTP, that the names of the SMTP service
@@ skipping 216 matching lines @@
         """
     debuglevel = 0
     file = None
     helo_resp = None
     ehlo_msg = "ehlo"
     ehlo_resp = None
     does_esmtp = 0
 
     def __init__(self, host='', port=0, local_hostname=None,
                  timeout=socket._GLOBAL_DEFAULT_TIMEOUT,
-                 source_address=('', 0)):
+                 source_address=None):
         """Initialize a new instance.
 
         If specified, `host' is the name of the remote host to which to
         connect.  If specified, `port' specifies the port to which to connect.
         By default, smtplib.SMTP_PORT is used.  An SMTPConnectError is raised
         if the specified `host' doesn't respond correctly.  If specified,
         `local_hostname` is used as the FQDN of the local host.  By default,
         the local hostname is found using socket.getfqdn(). The `source_address'
         parameter takes a 2-tuple (host, port) like socket.create_connection,
         for the socket to bind to as its source address before connecting.
@@ skipping 33 matching lines @@
         A non-false value results in debug messages for connection and for all
         messages sent to and received from the server.
 
         """
         self.debuglevel = debuglevel
 
     def _get_socket(self, host, port, timeout):
         # This makes it simpler for SMTP_SSL to use the SMTP connect code
         # and just alter the socket connection bit.
         if self.debuglevel > 0:
-            print('connect: to', (host, port)+self.source_address, file=stderr)
+            print('connect: to', (host, port), self.source_address, file=stderr)
         return socket.create_connection((host, port), timeout,
                                         self.source_address)
 
     def connect(self, host='localhost', port=0, source_address=None):
         """Connect to a host on a given port.
 
         If the hostname ends with a colon (`:') followed by a number, and
         there is no port specified, that suffix will be stripped off and the
         number interpreted as the port number to use.
 
@@ skipping 594 matching lines @@
         line = sys.stdin.readline()
         if not line:
             break
         msg = msg + line
     print("Message length is %d" % len(msg))
 
     server = SMTP('localhost')
     server.set_debuglevel(1)
     server.sendmail(fromaddr, toaddrs, msg)
     server.quit()