[Libguestfs] [nbdkit PATCH] python: Make sure callbacks are actually callable

[Eric Blake]

Rather than catching a Python error at runtime when trying to
call an object that wasn't callable, just ignore that object
up front when loading the plugin.

Signed-off-by: Eric Blake <eblake at redhat.com>
---

Various examples on calling Python functions from C recommend
doing this filtering check.

 plugins/python/python.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/plugins/python/python.c b/plugins/python/python.c
index 0206b80..35e8df2 100644
--- a/plugins/python/python.c
+++ b/plugins/python/python.c
@@ -94,6 +94,11 @@ callback_defined (const char *name, PyObject **obj_rtn)
   obj = PyObject_GetAttrString (module, name);
   if (!obj)
     return 0;
+  if (!PyCallable_Check (obj)) {
+    nbdkit_debug ("object %s isn't callable", name);
+    Py_DECREF (obj);
+    return 0;
+  }

   if (obj_rtn != NULL)
     *obj_rtn = obj;
-- 
2.14.3