iostream: Update comment

Update comment from #2690 about ssl module exceptions.

diff --git a/tornado/iostream.py b/tornado/iostream.py
index b11f65eedd1dda687ae9ef51daf207e6a12b77e5..1fe26ae6a8e3d13d29fa432502f8c286e51df823 100644 (file)
--- a/tornado/iostream.py
+++ b/tornado/iostream.py
@@ -1415,7 +1415,9 @@ class SSLIOStream(IOStream):
             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