--- a/Modules/_io/clinic/bufferedio.c.h	2018-01-01 01:22:36.000000000 -0500
+++ b/Modules/_io/clinic/bufferedio.c.h	2018-01-01 01:22:46.000000000 -0500
@@ -165,6 +165,23 @@
     return return_value;
 }
 
+PyDoc_STRVAR(_io__Buffered_getbuffn__doc__,
+"getbuffn($self, /)\n"
+"--\n"
+"\n");
+
+#define _IO__BUFFERED_GETBUFFN_METHODDEF    \
+    {"getbuffn", (PyCFunction)_io__Buffered_getbuffn, METH_NOARGS, _io__Buffered_getbuffn__doc__},
+
+static PyObject *
+_io__Buffered_getbuffn_impl(buffered *self);
+
+static PyObject *
+_io__Buffered_getbuffn(buffered *self, PyObject *Py_UNUSED(ignored))
+{
+    return _io__Buffered_getbuffn_impl(self);
+}
+
 PyDoc_STRVAR(_io__Buffered_readinto__doc__,
 "readinto($self, buffer, /)\n"
 "--\n"
--- a/Modules/_io/bufferedio.c	2017-12-18 23:53:56.000000000 -0500
+++ b/Modules/_io/bufferedio.c	2018-01-01 01:23:25.000000000 -0500
@@ -40,6 +40,7 @@
 _Py_IDENTIFIER(peek);
 _Py_IDENTIFIER(read);
 _Py_IDENTIFIER(read1);
+_Py_IDENTIFIER(getbuffn);
 _Py_IDENTIFIER(readable);
 _Py_IDENTIFIER(readinto);
 _Py_IDENTIFIER(readinto1);
@@ -187,6 +188,18 @@
     return bufferediobase_unsupported("read1");
 }
 
+
+PyDoc_STRVAR(bufferediobase_getbuffn_doc,
+    "Return the number of bytes buffered\n"
+    "on the underlying raw stream.\n");
+
+static PyObject *
+bufferediobase_getbuffn(PyObject *self, PyObject *args)
+{
+    return bufferediobase_unsupported("getbuffn");
+}
+
+
 PyDoc_STRVAR(bufferediobase_write_doc,
     "Write the given buffer to the IO stream.\n"
     "\n"
@@ -987,6 +1000,24 @@
 }
 
 static PyObject *
+_io__Buffered_getbuffn_impl(buffered *self)
+{
+    Py_ssize_t have;
+    PyObject *res = NULL;
+
+    CHECK_INITIALIZED(self)
+
+    CHECK_CLOSED(self, "read of closed file")
+
+    /* Return number of bytes buffered */
+    have = Py_SAFE_DOWNCAST(READAHEAD(self), Py_off_t, Py_ssize_t);
+    res = PyLong_FromSsize_t( have );
+    Py_INCREF(res);
+
+    return res;
+}
+
+static PyObject *
 _buffered_readinto_generic(buffered *self, Py_buffer *buffer, char readinto1)
 {
     Py_ssize_t n, written = 0, remaining;
@@ -2206,6 +2237,12 @@
 }
 
 static PyObject *
+bufferedrwpair_getbuffn(rwpair *self, PyObject *args)
+{
+    return _forward_call(self->reader, &PyId_getbuffn, args);
+}
+
+static PyObject *
 bufferedrwpair_readinto(rwpair *self, PyObject *args)
 {
     return _forward_call(self->reader, &PyId_readinto, args);
@@ -2342,6 +2379,7 @@
     _IO__BUFFEREDIOBASE_DETACH_METHODDEF
     {"read", bufferediobase_read, METH_VARARGS, bufferediobase_read_doc},
     {"read1", bufferediobase_read1, METH_VARARGS, bufferediobase_read1_doc},
+    {"getbuffn", bufferediobase_getbuffn, METH_NOARGS, bufferediobase_getbuffn_doc},
     _IO__BUFFEREDIOBASE_READINTO_METHODDEF
     _IO__BUFFEREDIOBASE_READINTO1_METHODDEF
     {"write", bufferediobase_write, METH_VARARGS, bufferediobase_write_doc},
@@ -2416,6 +2454,7 @@
     _IO__BUFFERED_READ_METHODDEF
     _IO__BUFFERED_PEEK_METHODDEF
     _IO__BUFFERED_READ1_METHODDEF
+    _IO__BUFFERED_GETBUFFN_METHODDEF
     _IO__BUFFERED_READINTO_METHODDEF
     _IO__BUFFERED_READINTO1_METHODDEF
     _IO__BUFFERED_READLINE_METHODDEF
@@ -2584,6 +2623,7 @@
     {"read", (PyCFunction)bufferedrwpair_read, METH_VARARGS},
     {"peek", (PyCFunction)bufferedrwpair_peek, METH_VARARGS},
     {"read1", (PyCFunction)bufferedrwpair_read1, METH_VARARGS},
+    {"getbuffn", (PyCFunction)bufferedrwpair_getbuffn, METH_NOARGS},
     {"readinto", (PyCFunction)bufferedrwpair_readinto, METH_VARARGS},
     {"readinto1", (PyCFunction)bufferedrwpair_readinto1, METH_VARARGS},
 
@@ -2678,6 +2718,7 @@
     _IO__BUFFERED_TRUNCATE_METHODDEF
     _IO__BUFFERED_READ_METHODDEF
     _IO__BUFFERED_READ1_METHODDEF
+    _IO__BUFFERED_GETBUFFN_METHODDEF
     _IO__BUFFERED_READINTO_METHODDEF
     _IO__BUFFERED_READINTO1_METHODDEF
     _IO__BUFFERED_READLINE_METHODDEF