BytesIO.getvalue() and StringIO.getvalue() are METH_NOARGS.
diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
index 4e78cd5..3ef9e2e 100644
--- a/Modules/_io/bytesio.c
+++ b/Modules/_io/bytesio.c
@@ -818,7 +818,7 @@
{"readline", (PyCFunction)bytesio_readline, METH_VARARGS, readline_doc},
{"readlines", (PyCFunction)bytesio_readlines, METH_VARARGS, readlines_doc},
{"read", (PyCFunction)bytesio_read, METH_VARARGS, read_doc},
- {"getvalue", (PyCFunction)bytesio_getvalue, METH_VARARGS, getval_doc},
+ {"getvalue", (PyCFunction)bytesio_getvalue, METH_NOARGS, getval_doc},
{"seek", (PyCFunction)bytesio_seek, METH_VARARGS, seek_doc},
{"truncate", (PyCFunction)bytesio_truncate, METH_VARARGS, truncate_doc},
{"__getstate__", (PyCFunction)bytesio_getstate, METH_NOARGS, NULL},