Re: [Jython-users] read only attributes

[Jose M. R. <jm...@in...>]

My first was attempt was to define a bean property function, only a 
getter and no
setter for the read only property. Unfortunately my java class simulates 
a Python
module and the static getter for the module property is not recognized 
as a property,
I think that getters / setters only work for instance properties. Is 
this inteded? I
expected that a function like "public static String getFoo()" defined a 
class property.

I followed your suggestion and derived a new PyObject class based on
PyBeanProperties that is suited for class properties, it worked fine. 
The code is:

<cutHere-->
public class PyStaticBeanProperty extends PyObject {

    public Method getMethod;

    public Method setMethod;

    public Class myType;

    String name;

    public PyStaticBeanProperty(String name, Class myType, Method 
getMethod,
            Method setMethod) {
        this.name = name;
        this.getMethod = getMethod;
        this.setMethod = setMethod;
        this.myType = myType;
    }

    public PyObject _doget(PyObject self) {
        if (self != null) {
            throw Py.AttributeError("attribute: "+ name +
                " is not an instance attribute");
        }
        if (getMethod == null) {
            throw Py.AttributeError("write-only attr: " + name);
        }
        try {
            Object value = getMethod.invoke(null, Py.EmptyObjects);
            return Py.java2py(value);
        } catch (Exception e) {
            throw Py.JavaError(e);
        }
    }

    public boolean _doset(PyObject self, PyObject value) {
        if (self != null) {
            throw Py.AttributeError("attribute: " + name +
                " is not an instance attributre");
        }
        if (setMethod == null) {
            throw Py.AttributeError("read-only attr: " + name);
        }

        Object jvalue = null;

        // Special handling of tuples
        // try to call a class constructor
        if (value instanceof PyTuple) {
            try {
                PyTuple vtup = (PyTuple) value;
                value = PyJavaClass.lookup(myType).__call__(vtup.list);
            } catch (Throwable t) {
                // If something goes wrong ignore it?
            }
        }
        if (jvalue == null) {
            jvalue = Py.tojava(value, myType);
        }
        try {
            setMethod.invoke(null, new Object[] { jvalue });
        } catch (Exception e) {
            throw Py.JavaError(e);
        }
        return true;
    }

    public PyStaticBeanProperty copy() {
        return new PyStaticBeanProperty(name, myType, getMethod, setMethod);
    }

    public String toString() {
        String typeName = "unknown";
        if (myType != null) {
            typeName = myType.getName();
        }
        return "<staticBeanProperty "+ name +" type: "+ typeName +" at " +
            Py.id(this) + ">";
    }
}
</cutHere>

Now I can write something like:
            dict.__setitem__("foo", new PyStaticBeanProperty("foo",
                    String.class, getter, null));
and obtain a read only property.

I think that a Wiki for Jython would be great, so users can contribute 
in the
documentation, explain tips, help other users, etc.

Regards,
    Jose . Rus

Jeff Emanuel wrote:

>Jose,
>
>This is simple if you rely on Jython bean
>property access.  If your Java class has
>a getFoo method but no setFoo, then foo
>would be read only.  
>
>Since you are adding your own custom attribute
>objects to the dictionary, you can make the
>_doset method of the PyObjects you put in the
>dictionary throw a Py.AttributeError.  That's
>how PyBeanProperty implements read-only
>attributes.
>
>Jeff
>
>
>-----Original Message-----
>From: Jose M. Rus [mailto:jm...@in...]
>Sent: Monday, October 06, 2003 10:35 AM
>To: jyt...@li...
>Subject: [Jython-users] read only attributes
>
>
>Hi list,
>
>I have a java class that emulates a Python module. It implements 
>ClassDictInit and
>it defines some attributes in his own dictionary. Now I want to make one 
>of them
>read only.
>
>What is the recommended way of doing this?
>
>Thanks.
>
>
>
>
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