RE: [Jython-users] Jython pyDictionary to Java HashMap conversion

[Updike, C. <Cla...@jh...>]

I created a class that exposes a public Map field that stays sync'd
with the underlying jython dictionary.  You can instantiate is using
either a dictionary or a map.  Here's the code and an example
demonstrating it in jython below.

I keep meaning to try the same thing for a list but haven't gotten
around to it.

-Clark

---------------------------------------------------------------------

import java.util.Collections;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;

import org.python.core.Py;
import org.python.core.PyDictionary;
import org.python.core.PyList;
import org.python.core.PyTuple;

/**
 * Exposes an unmodifiable java.util.Map as a public field
 * directly accessible from Jython.  The map reflects
 * changes made through the PyDictionary methods.
 *
 * @see java.util.Map
 * @author clark
 */
public class PyJavaDictionary extends PyDictionary {

    /** The underlying dictionary PyDictionary exposed as an
     * unmodifyable Map.
     */
    public final Map map;
   
    /** Initializes to the values contained in <code>aMap</code>.
     */
    public PyJavaDictionary(Map aMap) {
   
        Map tmpMap = new HashMap();
        Iterator it = aMap.entrySet().iterator();
        while(it.hasNext()) {
          Map.Entry e = (Map.Entry)it.next();
          tmpMap.put(Py.java2py(e.getKey()),
            Py.java2py(e.getValue()));
        }

        table = new Hashtable(tmpMap);     
        map = Collections.unmodifiableMap(table);  
    }

    /** Initializes to the values contained in <code>dict</code>.
     * Use this to construct from a native jython dictionary.
     */
    public PyJavaDictionary(PyDictionary dict) {
       
        PyList list = dict.items();
        table = new Hashtable();
       
        for(int i = list.__len__(); i-- > 0; ) {
            PyTuple tup = (PyTuple)list.__getitem__(i);
            table.put(tup.__getitem__(0), tup.__getitem__(1));
        }
        map = Collections.unmodifiableMap(table);
    }
}

---------------------------------------------------------------------

Jython 2.1 on java1.3.1_01 (JIT: null)
Type "copyright", "credits" or "license" for more information.
>>> import PyJavaDictionary as PJD
>>> d = {'a':1, 'b':2, 'c':3}
>>>
>>> # create from a Jython Dictionary
>>> pjd=PJD(d)
>>> pjd
{'b': 2, 'a': 1, 'c': 3}
>>> pjd.keys()
['b', 'a', 'c']
>>> pjd.values()
[2, 1, 3]
>>> pjd['x']=25
>>> pjd
{'x': 25, 'b': 2, 'a': 1, 'c': 3}
>>> pjd.map
{x=25, b=2, a=1, c=3}
>>>
>>> # are they still in synch?
>>> pjd == PJD(pjd.map) and "YES" or "NO"
'YES'
>>>
>>> # but don't try to modify the map field!
>>> pjd.map.put('y',25)
Traceback (innermost last):
  File "<console>", line 1, in ?
java.lang.UnsupportedOperationException
        at java.util.Collections$UnmodifiableMap.put(Collections.java:817)
        at java.lang.reflect.Method.invoke(Native Method)
<snip>    
>>> pjd.map.keySet()
[x, b, a, c]
>>>
>>> # create from a Map instance (just reuse the one from pjd)
>>> pjd2=PJD(pjd.map)
>>> pjd2
{'x': 25, 'b': 2, 'a': 1, 'c': 3}
>>>
>>> pjd2['y']=25
>>> pjd2
{'x': 25, 'b': 2, 'a': 1, 'y': 25, 'c': 3}
>>>
>>> pjd2.map
{x=25, b=2, a=1, y=25, c=3}
>>>
>>> # are they still in synch?
>>> PJD(pjd2.map)==pjd2 and "YES" or "NO"
'YES'

---------------------------------------------------------------------

-----Original Message-----
From: Si Chen
Sent: Friday, December 19, 2003 6:19 PM
To: jyt...@li...
Subject: [Jython-users] Jython pyDictionary to Java HashMap conversion


Hello.  I have to return a java.util.Hashmap from my jython code, and I
just realized that it is not an automatic conversion.  For example,

 >>> pyMap = {"a":1,"b":2,"c":3}
 >>> pyMap.__class__
<jclass org.python.core.Pydictionary at ....>
 >>> from java.util import Hashmap
 >>> jMap = HashMap(pyMap)
TypeError: java.util.HashMap(): 1st arg can't be coerced into int or
java.util.Map

I have not tried lists or arrays.  Is there a way to automatically
convert these back to java equivalents, or must I use the Java
constructors and write Java code to have them properly returned as Java
classes?

Thanks in advance,

Si Chen