seek() returns an int everywhere.

pep-3116.txt

@@ -82,7 +82,7 @@ exactly one operating system call.
 
         Returns number of bytes written, which may be ``< len(b)``.
 
-    ``.seek(pos: int, whence: int = 0) -> None``
+    ``.seek(pos: int, whence: int = 0) -> int``
 
     ``.tell() -> int``
 
@@ -283,7 +283,7 @@ per-character basis instead of a per-byte basis.  These methods are:
         The only supported use for the cookie is with .seek()
         with whence set to 0 (i.e. absolute seek).
 
-    ``.seek(pos: object, whence: int = 0) -> None``
+    ``.seek(pos: object, whence: int = 0) -> int``
 
         Seek to position ``pos``.  If ``pos`` is non-zero, it must
         be a cookie returned from ``.tell()`` and ``whence`` must be zero.