socket.error inherits from IOError, it no longer needs listing in
the all_errors tuple.
diff --git a/Lib/ftplib.py b/Lib/ftplib.py
index 3a9f994..a915b2d 100644
--- a/Lib/ftplib.py
+++ b/Lib/ftplib.py
@@ -65,7 +65,7 @@
 
 # All exceptions (hopefully) that may be raised here and that aren't
 # (always) programming errors on our side
-all_errors = (Error, socket.error, IOError, EOFError)
+all_errors = (Error, IOError, EOFError)
 
 
 # Line terminators (we always output CRLF, but accept any of CRLF, CR, LF)