#13530: port to 2.7 branch (document what os.lseek returns).

Doc/library/os.rst

@@ -744,7 +744,7 @@ as internal buffering of data.
    by *how*: :const:`SEEK_SET` or ``0`` to set the position relative to the
    beginning of the file; :const:`SEEK_CUR` or ``1`` to set it relative to the
    current position; :const:`SEEK_END` or ``2`` to set it relative to the end of
-   the file.
+   the file. Return the new cursor position in bytes, starting from the beginning.
 
    Availability: Unix, Windows.
 

Modules/posixmodule.c

@@ -6667,7 +6667,8 @@ posix_dup2(PyObject *self, PyObject *args)
 
 PyDoc_STRVAR(posix_lseek__doc__,
 "lseek(fd, pos, how) -> newpos\n\n\
-Set the current position of a file descriptor.");
+Set the current position of a file descriptor.\n\
+Return the new cursor position in bytes, starting from the beginning.");
 
 static PyObject *
 posix_lseek(PyObject *self, PyObject *args)