Suggestions for #4 (returning None) and #2 (logging server responses)

* removed unused "import socket"
* changed broad "except" clause to more specific "except ImportError"
* general PEP8 reformat
* added "debug" option for logging server responses/errors
* return None instead of True/False on several errors that may be temporary

validate_email.py

@@ -19,14 +19,17 @@
 
 import re
 import smtplib
-import socket
+import logging
 
 try:
     import DNS
     ServerError = DNS.ServerError
-except:
+except ImportError:
     DNS = None
-    class ServerError(Exception): pass
+
+    class ServerError(Exception):
+        pass
+
 # All we are really doing is comparing the input string to one
 # gigantic regular expression.  But building that regexp, and
 # ensuring its correctness, is made much easier by assembling it
@@ -50,7 +53,7 @@ CTEXT = r'[' + NO_WS_CTL + \
         r'\x21-\x27\x2a-\x5b\x5d-\x7e]'              # see 3.2.3
 CCONTENT = r'(?:' + CTEXT + r'|' + \
            QUOTED_PAIR + r')'                        # see 3.2.3 (NB: The RFC includes COMMENT here
-                                                                                                         # as well, but that would be circular.)
+# as well, but that would be circular.)
 COMMENT = r'\((?:' + FWS + r'?' + CCONTENT + \
           r')*' + FWS + r'?\)'                       # see 3.2.3
 CFWS = r'(?:' + FWS + r'?' + COMMENT + ')*(?:' + \
@@ -81,8 +84,8 @@ ADDR_SPEC = LOCAL_PART + r'@' + DOMAIN               # see 3.4.1
 # A valid address will match exactly the 3.4.1 addr-spec.
 VALID_ADDRESS_REGEXP = '^' + ADDR_SPEC + '$'
 
-def validate_email(email, check_mx=False,verify=False):
 
+def validate_email(email, check_mx=False, verify=False, debug=False):
     """Indicate whether the given string is a valid email address
     according to the 'addr-spec' portion of RFC 2822 (see section
     3.4.1).  Parts of the spec that are marked obsolete are *not*
@@ -90,13 +93,20 @@ def validate_email(email, check_mx=False,verify=False):
     depend on circular definitions in the spec may not pass, but in
     general this should correctly identify any email address likely
     to be in use as of 2011."""
+    if debug:
+        logger = logging.getLogger('validate_email')
+    else:
+        logger = None
+
     try:
         assert re.match(VALID_ADDRESS_REGEXP, email) is not None
         check_mx |= verify
         if check_mx:
-            if not DNS: raise Exception('For check the mx records or check if the email exists you must have installed pyDNS python package')
+            if not DNS:
+                raise Exception('For check the mx records or check if the email exists you must '
+                                'have installed pyDNS python package')
             DNS.DiscoverNameServers()
-            hostname = email[email.find('@')+1:]
+            hostname = email[email.find('@') + 1:]
             mx_hosts = DNS.mxlookup(hostname)
             for mx in mx_hosts:
                 try:
@@ -108,20 +118,30 @@ def validate_email(email, check_mx=False,verify=False):
                     status, _ = smtp.helo()
                     if status != 250:
                         smtp.quit()
+                        if debug:
+                            logger.debug(u'%s answer: %s - %s', mx[1], status, _)
                         continue
                     smtp.mail('')
                     status, _ = smtp.rcpt(email)
-                    if status != 250:
+                    if status == 250:
                         smtp.quit()
-                        return False
+                        return True
+                    if debug:
+                        logger.debug(u'%s answer: %s - %s', mx[1], status, _)
                     smtp.quit()
-                    break
+                except smtplib.SMTPServerDisconnected:  # Server not permits verify user
-                except smtplib.SMTPServerDisconnected: #Server not permits verify user
+                    if debug:
-                    break
+                        logger.debug(u'%s disconected.', mx[1])
                 except smtplib.SMTPConnectError:
-                    continue
+                    if debug:
-    except (AssertionError, ServerError): 
+                        logger.debug(u'Unable to connect to %s.', mx[1])
+            return None
+    except AssertionError:
         return False
+    except ServerError:
+        if debug:
+            logger.debug(u'ServerError exception raised.')
+        return None
     return True
 
 # import sys