Re: Having to "print" before method invocation?
- From: "Fredrik Lundh" <fredrik@xxxxxxxxxxxxxx>
- Date: Wed, 8 Mar 2006 15:41:31 +0100
Jeremy L. Moles wrote:
I have an object (written as part C extension, part pure Python) called
foo that I've been using without much fuss for a few months now.
However, in my latest project (a rather large one involving
multi-threading, pygtk, etc.), I'm seeing some really strange behavior
with a particular instance of my foo object.
About midway through my program, any attempt to use the instance fails;
however, if I add print statements before trying to invoke methods on
it, the foo object instance works fine.
fails in what way?
if you get a spurious exception, it's very likely that your C extension sets the
exception state (either directly or because some API function it uses fails), but
forgets to report this back to Python.
e.g. if you have a C function that does something like
PyErr_SetString(PyExc_AttributeError, "blah blah"):
Py_INCREF(Py_None);
return Py_None;
instead of
PyErr_SetString(PyExc_AttributeError, "blah blah"):
return NULL;
the interpreter won't raise the exception immediately (since it expected you to
return NULL if something went wrong), but the exception may still be raised at
a later time, if you run interpreter code that does something like
do something
if (PyErr_Occurred())
... /* this will catch your error even if "something" succeeds */ ...
*or* it may be masked, by code that does
PyErr_Clear();
do something
the actual exception might give you additional clues (e.g. if you get a KeyError,
look for unchecked dictionary accesses in your code, etc).
hope this helps!
</F>
.
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