Removed some unused imports to decrease the amount of loaded modules during startup.

Added fallback to _dummy_thread for OSs w/o thread support.

Lib/io.py

@@ -60,8 +60,12 @@ import abc
 import sys
 import codecs
 import _fileio
-import warnings
-from _thread import allocate_lock as Lock
+# Import _thread instead of threading to reduce startup cost
+try:
+    from _thread import allocate_lock as Lock
+except ImportError:
+    from _dummy_thread import allocate_lock as Lock
+
 
 # open() uses st_blksize whenever we can
 DEFAULT_BUFFER_SIZE = 8 * 1024  # bytes

Lib/warnings.py

@@ -5,7 +5,6 @@
 # See bug 683658.
 import linecache
 import sys
-import types
 
 __all__ = ["warn", "showwarning", "formatwarning", "filterwarnings",
            "resetwarnings"]