Merge pull request tornadoweb#2847 from tornadoweb/bdarnell-patch-1

iostream: Update comment

Author: bdarnell

tornado/iostream.py

@@ -1415,7 +1415,9 @@ def _do_ssl_handshake(self) -> None:
             raise
         except ssl.CertificateError as err:
             # CertificateError can happen during handshake (hostname
-            # verification) and should be passed to user
+            # verification) and should be passed to user. Starting
+            # in Python 3.7, this error is a subclass of SSLError
+            # and will be handled by the previous block instead.
             return self.close(exc_info=err)
         except socket.error as err:
             # Some port scans (e.g. nmap in -sT mode) have been known