Updated the socketpair() docstring and documentation to explain that the

default famility is AF_UNIX if defined for the platform, otherwise the
default is AF_INET.

Doc/lib/libsocket.tex

@@ -307,8 +307,9 @@ success, a new \class{SSLObject} is returned.
 Build a pair of connected socket objects using the given address
 family, socket type and protocol number.  Address family, socket type
 and protocol number are as for the \function{socket()} function above.
-Availability: \UNIX.
-\versionadded{2.4}
+The default family is AF_UNIX if defined for the platform, otherwise
+the default is AF_INET.
+Availability: \UNIX.  \versionadded{2.4}
 \end{funcdesc}
 
 \begin{funcdesc}{fromfd}{fd, family, type\optional{, proto}}

Modules/socketmodule.c

@@ -3011,7 +3011,8 @@ Return the protocol number for the named protocol.  (Rarely used.)");
 
 #ifdef HAVE_SOCKETPAIR
 /* Create a pair of sockets using the socketpair() function.
-   Arguments as for socket(). */
+   Arguments as for socket() except the default family is AF_UNIX if
+   defined for the platform, otherwise the default is AF_INET. */
 
 /*ARGSUSED*/
 static PyObject *
@@ -3058,7 +3059,8 @@ PyDoc_STRVAR(socketpair_doc,
 \n\
 Create a pair of socket objects from the sockets returned by the platform\n\
 socketpair() function.\n\
-The arguments are the same as for socket().");
+The arguments are the same as for socket() except the default family is\n\
+AF_UNIX if defined for the platform, otherwise the default is AF_INET.");
 
 #endif /* HAVE_SOCKETPAIR */