Index: Doc/library/os.rst
===================================================================
--- Doc/library/os.rst	(revision 83045)
+++ Doc/library/os.rst	(working copy)
@@ -1126,17 +1126,19 @@
    Availability: Unix, Windows.
 
 
-.. function:: makedirs(path[, mode])
+.. function:: makedirs(path[, mode][, exist_ok=False])
 
    .. index::
       single: directory; creating
       single: UNC paths; and os.makedirs()
 
    Recursive directory creation function.  Like :func:`mkdir`, but makes all
-   intermediate-level directories needed to contain the leaf directory.  Throws
-   an :exc:`error` exception if the leaf directory already exists or cannot be
-   created.  The default *mode* is ``0o777`` (octal).  On some systems, *mode*
-   is ignored. Where it is used, the current umask value is first masked out.
+   intermediate-level directories needed to contain the leaf directory.  If 
+   the directory already exists, throws an :exc:`OSError` exception if 
+   *exist_ok* is Flase, otherwise no exception is thrown.  If the directory 
+   cannot be created, throws an :exc:`error` exception.  The default *mode* 
+   is ``0o777`` (octal).  On some systems, *mode* is ignored. Where it is 
+   used, the current umask value is first masked out.
 
    .. note::
 
Index: Lib/os.py
===================================================================
--- Lib/os.py	(revision 83045)
+++ Lib/os.py	(working copy)
@@ -119,13 +119,14 @@
 # Super directory utilities.
 # (Inspired by Eric Raymond; the doc strings are mostly his)
 
-def makedirs(name, mode=0o777):
-    """makedirs(path [, mode=0o777])
+def makedirs(name, mode=0o777, exist_ok=False):
+    """makedirs(path [, mode=0o777][, exist_ok=False])
 
     Super-mkdir; create a leaf directory and all intermediate ones.
     Works like mkdir, except that any intermediate path segment (not
-    just the rightmost) will be created if it does not exist.  This is
-    recursive.
+    just the rightmost) will be created if it does not exist.  If the
+    target directory already exists, throws an OSError if exist_ok is
+    False, otherwise no exception is thrown.  This is recursive.
 
     """
     head, tail = path.split(name)
@@ -133,14 +134,18 @@
         head, tail = path.split(head)
     if head and tail and not path.exists(head):
         try:
-            makedirs(head, mode)
+            makedirs(head, mode, exist_ok)
         except OSError as e:
             # be happy if someone already created the path
             if e.errno != errno.EEXIST:
                 raise
         if tail == curdir:           # xxx/newdir/. exists if xxx/newdir exists
             return
-    mkdir(name, mode)
+    try:
+        mkdir(name, mode)
+    except OSError as e:
+        if not (e.errno == errno.EEXIST and exist_ok):
+            raise
 
 def removedirs(name):
     """removedirs(path)
Index: Lib/test/test_os.py
===================================================================
--- Lib/test/test_os.py	(revision 83045)
+++ Lib/test/test_os.py	(working copy)
@@ -609,6 +609,14 @@
                             'dir5', 'dir6')
         os.makedirs(path)
 
+    def test_exist_ok(self):
+        base = support.TESTFN
+        path = os.path.join(support.TESTFN, 'dir1')
+        os.makedirs(path)
+        self.assertRaises(OSError, os.makedirs, path)
+        self.assertRaises(OSError, os.makedirs, path, exist_ok=False)
+        os.makedirs(path, exist_ok=True)
+
     def tearDown(self):
         path = os.path.join(support.TESTFN, 'dir1', 'dir2', 'dir3',
                             'dir4', 'dir5', 'dir6')