Issue1663

Our code uses a displayhook (see www.python.org/dev/peps/pep-0217/). It works in Jython 2.5.1, but fails in 2.5.1rc1 and 2.5.2rc2 with the following traceback:

2010-10-01 10:36:26,318 WARN  [gda.jython.GDAInteractiveConsole] - InteractiveConsole exception: Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: displayhook(): expected 1 args; got 0

org.python.core.PyException
	at org.python.core.PyException.fillInStackTrace(PyException.java:70) [jython.jar:na]
	at java.lang.Throwable.<init>(Throwable.java:181) [na:1.6.0_16]
	at java.lang.Exception.<init>(Exception.java:29) [na:1.6.0_16]
	at java.lang.RuntimeException.<init>(RuntimeException.java:32) [na:1.6.0_16]
	at org.python.core.PyException.<init>(PyException.java:46) [jython.jar:na]
	at org.python.core.PyException.<init>(PyException.java:43) [jython.jar:na]
	at org.python.core.PyException.<init>(PyException.java:61) [jython.jar:na]
	at org.python.core.Py.TypeError(Py.java:221) [jython.jar:na]
	at org.python.core.PyReflectedFunction.throwError(PyReflectedFunction.java:209) [jython.jar:na]
	at org.python.core.PyReflectedFunction.throwArgCountError(PyReflectedFunction.java:262) [jython.jar:na]
	at org.python.core.PyReflectedFunction.throwError(PyReflectedFunction.java:319) [jython.jar:na]
	at org.python.core.PyReflectedFunction.__call__(PyReflectedFunction.java:167) [jython.jar:na]
	at org.python.core.PyReflectedFunction.__call__(PyReflectedFunction.java:204) [jython.jar:na]
	at org.python.core.PyObject.__call__(PyObject.java:387) [jython.jar:na]
	at org.python.core.PyObject.invoke(PyObject.java:3585) [jython.jar:na]
	at org.python.core.Py.printResult(Py.java:1792) [jython.jar:na]
	at org.python.pycode._pyx69.f$0(<input>:1) [na:na]
	at org.python.pycode._pyx69.call_function(<input>) [na:na]
	at org.python.core.PyTableCode.call(PyTableCode.java:165) [jython.jar:na]
	at org.python.core.PyCode.call(PyCode.java:18) [jython.jar:na]
	at org.python.core.Py.runCode(Py.java:1253) [jython.jar:na]
	at org.python.core.Py.exec(Py.java:1297) [jython.jar:na]
	at org.python.util.PythonInterpreter.exec(PythonInterpreter.java:215) [jython.jar:na]
	at org.python.util.InteractiveInterpreter.runcode(InteractiveInterpreter.java:89) [jython.jar:na]
	at org.python.util.InteractiveInterpreter.runsource(InteractiveInterpreter.java:70) [jython.jar:na]
	at org.python.util.InteractiveInterpreter.runsource(InteractiveInterpreter.java:42) [jython.jar:na]
	at gda.jython.GDAJythonInterpreter.populateNamespace(GDAJythonInterpreter.java:493) [main/:na]
	at gda.jython.GDAJythonInterpreter.initialise(GDAJythonInterpreter.java:463) [main/:na]
	at gda.jython.JythonServer.configure(JythonServer.java:338) [main/:na]
	at gda.factory.FactoryBase.configure(FactoryBase.java:64) [main/:na]
	at gda.util.ObjectCreatorsObjectServer.startServer(ObjectCreatorsObjectServer.java:288) [main/:na]
	at gda.util.ObjectServer.configure(ObjectServer.java:335) [main/:na]
	at gda.util.ObjectServer.createServerImpl(ObjectServer.java:133) [main/:na]
	at gda.util.ObjectServer.main(ObjectServer.java:503) [main/:na]
2010-10-01 10:36:26,424 WARN  [gda.jython.GDAInteractiveConsole] - InteractiveConsole exception: Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: displayhook(): expected 1 args; got 0


displayhook itself is fairly simple:
    public static void displayhook(PyObject o) {
        /* Print value except if None */
        /* After printing, also assign to '_' */
        /* Before, set '_' to None to avoid recursion */
        if (o == Py.None)
             return;

        PyObject currentBuiltins = Py.getSystemState().getBuiltins();
        currentBuiltins.__setitem__("_", Py.None);
        if (o instanceof PyUnicode) {
        	PyUnicode u = (PyUnicode)o;
			Py.println(u.__str__());
		} else {
			Py.println(o.__repr__());
		}
        currentBuiltins.__setitem__("_", o);
    }


Unfortunately this is part of a fairly large code base, and at this point I haven't pulled out a simple test case for you.

A quick glance at the change log doesn't throw up any obvious candidates.

Correction to above:
OLD: fails in 2.5.1rc1 and 2.5.2rc2
NEW: fails in 2.5.2rc1 and 2.5.2rc2

OK, I think we've found where the problem was introduced:

Revision 6837
hack around PyReflectedFunction's assumption of how instancemethod calls into
it so instancemethod's ThreadState pass through optimization can be enabled

The problem is in PyReflectedFunction.java, in this method: 
public PyObject __call__(PyObject[] args, String[] keywords) {
(it's line 194 in revision 7066).

I don't have enough understanding of how all this fits together to suggest a fix (the comment in line 48
    // NOTE: this calledStatically business is pretty hacky
suggests only the brave should touch this code).

However, I hope that's enough to get you started.

I can't reproduce this problem on Jython trunk. Here's what I tried:

>>> import dh    
>>> import sys
>>> h = dh()
>>> h.hook("hi")
Hooked<<<hi>>>
>>> sys.displayhook = h.hook
>>> "foo"                   
Hooked<<<foo>>>
>>> sys.displayhook = dh.static_hook
>>> "foo"                           
Hooked<<<foo>>>

This is the dh class:

import org.python.core.PyObject;

public class dh {

    public dh() {}

    public static void static_hook(PyObject o) {
        System.out.println("Hooked<<<" + o + ">>>");
    }

    public void hook(PyObject o) {
        System.out.println("Hooked<<<" + o + ">>>");
    }
    
}

So that all looks good to me.

Please submit a test case (in either JUnit or PyUnit, see our test cases for examples) and reopen if you're still experiencing a problem. I did take a look at the possibility of downloading  and running GDA, but that's just too big of a project.