Issue #13087: BufferedReader.seek() now always raises UnsupportedOperation
if the underlying raw stream is unseekable, even if the seek could be
satisfied using the internal buffer. Patch by John O'Connor.
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index d6f0c9c..bd1aae5 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -1086,6 +1086,9 @@
CHECK_CLOSED(self, "seek of closed file")
+ if (_PyIOBase_check_seekable(self->raw, Py_True) == NULL)
+ return NULL;
+
target = PyNumber_AsOff_t(targetobj, PyExc_ValueError);
if (target == -1 && PyErr_Occurred())
return NULL;