Issue #5870: Add subprocess.DEVNULL constant.
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index 4a12b76..88eb784 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -125,12 +125,14 @@
 
    *stdin*, *stdout* and *stderr* specify the executed programs' standard input,
    standard output and standard error file handles, respectively.  Valid values
-   are :data:`PIPE`, an existing file descriptor (a positive integer), an
-   existing :term:`file object`, and ``None``.  :data:`PIPE` indicates that a
-   new pipe to the child should be created.  With ``None``, no redirection will
-   occur; the child's file handles will be inherited from the parent.  Additionally,
-   *stderr* can be :data:`STDOUT`, which indicates that the stderr data from the
-   applications should be captured into the same file handle as for stdout.
+   are :data:`PIPE`, :data:`DEVNULL`, an existing file descriptor (a positive
+   integer), an existing :term:`file object`, and ``None``.  :data:`PIPE`
+   indicates that a new pipe to the child should be created.  :data:`DEVNULL`
+   indicates that the special file :data:`os.devnull` will be used. With ``None``,
+   no redirection will occur; the child's file handles will be inherited from
+   the parent.  Additionally, *stderr* can be :data:`STDOUT`, which indicates
+   that the stderr data from the applications should be captured into the same
+   file handle as for stdout.
 
    If *preexec_fn* is set to a callable object, this object will be called in the
    child process just before the child is executed.
@@ -229,6 +231,15 @@
       Added context manager support.
 
 
+.. data:: DEVNULL
+
+   Special value that can be used as the *stdin*, *stdout* or *stderr* argument
+   to :class:`Popen` and indicates that the special file :data:`os.devnull`
+   will be used.
+
+   .. versionadded:: 3.3
+
+
 .. data:: PIPE
 
    Special value that can be used as the *stdin*, *stdout* or *stderr* argument