[Jython-bugs] [ jython-Bugs-1462188 ] NullPointerException on accessing __doc__ attribute

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Bugs item #1462188, was opened at 2006-03-31 18:42
Message generated for change (Comment added) made by gene9
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Alex Stoddard (astoddar)
Assigned to: Nobody/Anonymous (nobody)
Summary: NullPointerException on accessing __doc__ attribute

Initial Comment:
Under jython 2.2 (latest and previous build) attempting to access 
specifically the __doc__ attribute of objects of built in classes fails.
The example uses "dict" but the bug is not specific to this.  

Other classes may also be affected. The behavior was first seen 
introspecting the on an object of the PatternObject class in the re 
module.

E.g.

>>> d = dict()
>>> dir(d)
['__class__', '__cmp__', '__contains__', '__delattr__', '__delitem__', 
'__doc__', '__eq__', '__getattribute__', '__getitem__', '__hash__', '__init__', 
'__iter__', '__len__', '__ne__', '__new__', '__repr__', '__setattr__', 
'__setitem__', '__str__', '__unicode__', 'clear', 'copy', 'fromkeys', 'get', 
'has_key', 'items', 'iteritems', 'iterkeys', 'itervalues', 'keys', 'pop', 
'popitem', 'setdefault', 'update', 'values']
>>> d.__class__
<type 'dict'>
>>> d.__doc__
Traceback (innermost last):
  File "<console>", line 1, in ?
java.lang.NullPointerException
	at org.python.core.PyObject.getDoc(Unknown Source)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at 
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorIm
pl.java:39)
	at 
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAc
cessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:324)
	at org.python.core.PyGetSetDescr.__get__(Unknown Source)
	at org.python.core.PyObject.object___findattr__(Unknown Source)
	at org.python.core.PyObject.__findattr__(Unknown Source)
	at org.python.core.PyObject.__getattr__(Unknown Source)
	at org.python.pycode._pyx11.f$0(<console>:1)
	at org.python.pycode._pyx11.call_function(<console>)
	at org.python.core.PyTableCode.call(Unknown Source)
	at org.python.core.PyCode.call(Unknown Source)
	at org.python.core.Py.runCode(Unknown Source)
	at org.python.core.Py.exec(Unknown Source)
	at org.python.util.PythonInterpreter.exec(Unknown Source)
	at org.python.util.InteractiveInterpreter.runcode(Unknown Source)
	at org.python.util.InteractiveInterpreter.runsource(Unknown 
Source)
	at org.python.util.InteractiveInterpreter.runsource(Unknown 
Source)
	at org.python.util.InteractiveConsole.push(Unknown Source)
	at org.python.util.InteractiveConsole.interact(Unknown Source)
	at org.python.util.jython.main(Unknown Source)

java.lang.NullPointerException: java.lang.NullPointerException

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

Comment By: andrey sidorenko (gene9)
Date: 2006-04-28 14:13

Message:
Logged In: YES 
user_id=369541

> cvs diff PyObject.java
Index: PyObject.java
===================================================================
RCS file: /cvsroot/jython/jython/org/python/core/PyObject.java,v
retrieving revision 2.43
diff -r2.43 PyObject.java
388c388,394
<         PyObject doc = fastGetDict().__finditem__("__doc__");
---
>
>         PyObject dict = fastGetDict();
>         if(dict == null) {
>             return Py.None;
>         }
>
>         PyObject doc = dict.__finditem__("__doc__");

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

Comment By: Nobody/Anonymous (nobody)
Date: 2006-04-06 11:52

Message:
Logged In: NO 

It can be fixed the way that the NPE doesn't occur anymore.
But, if there is no documentation string for dict (and BTW,
for other built-in types as well), an AttributeError will be
thrown. So, what should we do ? Hm, when we look at CPython,
we can see that, here too, dict for example has a very poor
documentation string. The same applies to list. Maybe we
should simply return an empty string. 

What do others think ? 

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

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