Re: [Libguestfs] [PATCH libnbd v2 1/3] python: Allow Python callbacks to auto-retire by returning an integer.
On 8/11/19 5:26 AM, Richard W.M. Jones wrote:
See equivalent change for OCaml in
commit d881d160e1cd9c9964782300a7652ffb4e506c27.
If the Python callback doesn't return something which looks like an
integer, assume 0 instead of returning an error.
---
generator/generator | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/generator/generator b/generator/generator
index 55c4dfc..e5d9aaa 100755
--- a/generator/generator
+++ b/generator/generator
@@ -4234,7 +4234,12 @@ let print_python_binding name { args; optargs; ret; may_set_error
} =
pr " Py_DECREF (py_args);\n";
pr "\n";
pr " if (py_ret != NULL) {\n";
- pr " Py_DECREF (py_ret); /* return value is discarded */\n";
+ pr " if (PyLong_Check (py_ret))\n";
+ pr " ret = PyLong_AsLong (py_ret);\n";
If I'm reading the python documentation correctly, this only succeeds
for actual subtypes of PyLong (and not for other python types that have
an __int__ converter available). But I don't find that too restricting;
'return 1' is easier to type than 'return myobject' where myobject is
not a subtype of PyLong but could otherwise convert to 1. And even if
the user insists on using some sort of myobject for tracking the logic
on whether auto-retire is needed, they can spell longhand:
if myobject == 1:
return 1
return 0
to get the desired semantics if 'return myobject' doesn't do what they want.
+ pr " else\n";
+ pr " /* If it's not a long, just assume it's 0. */\n";
+ pr " ret = 0;\n";
Makes sense. Thus, only an explicit return of -1 or throwing an
exception will turn into a C return of -1, only an explicit return of 1
will turn into auto-retire, and anything else makes no difference.
ACK.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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