Import * statement failed to work on Jython 2.7.2

[Keita2]

I encountered the issue as below when executing Jython script.

**************************************************
Traceback (most recent call last):
  File "<string>", line 48, in loadProperties
NameError: global name 'Properties' is not defined
**************************************************
WASX7017E: Exception received while running file "deploy.py"; exception information: com.ibm.bsf.BSFException: exception from Jython:
Traceback (most recent call last):
  File "<string>", line 108, in <module>
  File "<string>", line 75, in loadProperties
SystemExit: -1

This error happened after Jython 2.7 upgraded to 2.7.2 , so didn't happen with same script on Jython 2.7.
By modifying import * to specify class , this issue was resolved.

Before：
from java.util import *
from java.util import *
from java.io import *

After ：
from java.util import Properties
from java.io import FileInputStream
from java.lang import System

Question
Import * seems to fail to work on Jython V2.7.2 . Is this issue due to bug on Jython 2.7.2 ?

[yogi1967]

What is the JDK version for both tests? What happens if you revert JDK to earlier version?

[Keita2]

The JDK version is as below.
Jython V2.7 and JDK 8.0.7.16 <-- OK
Jython V2.7.2 and JDK 8.0.8.0 <--NG

[Keita2]

I will check if the issue can be recreated with Jython V2.7.2 and other JDK level.

[yogi1967]

Ah ok. I saw a similar issue for JDK21. So I doubt it's the same issue...

[Keita2]

I confirmed the issue is recreated with older version.
So, this issue is assumed due to Jython upgrade.
Jython V2.7.2 and JDK 8.0.7.20 <--NG
Jython V2.7.2 and JDK 8.0.6.31 <--NG

Let me add information about JDK. I use IBM Java .

[robertpatrick]

@jeff5 assuming this worked in 2.7 and before, this seems like a bug.

[jeff5]

import just goes on giving (#105, #304). However, I'm not able to reproduce this (on Windows) with:

Jython 2.7.2 (v2.7.2:925a3cc3b49d, Mar 21 2020, 10:03:58)
[Java HotSpot(TM) 64-Bit Server VM (Oracle Corporation)] on java1.8.0_321
Type "help", "copyright", "credits" or "license" for more information.
>>> globals().keys()
['__builtins__', '__doc__', '__name__', '__package__']
>>> from java.util import *
>>> from java.io import *
>>> from java.lang import *
>>> len(globals().keys())
300
>>> Properties
<type 'java.util.Properties'>
>>> System
<type 'java.lang.System'>
>>> FileInputStream
<type 'java.io.FileInputStream'>

It's the same in the development tip locally.

[Keita2]

@jeff5 On Mac, this can be recreated as follows.
But I am not able to recreate on Windows.
Could you try to recreate on Unix environment ?

Mac

% java -jar jython.jar
Jython 2.7.3 (tags/v2.7.3:5f29801fe, Sep 10 2022, 18:52:49)
[Java HotSpot(TM) 64-Bit Server VM (Oracle Corporation)] on java1.8.0_333
Type "help", "copyright", "credits" or "license" for more information.
>>> from java.util import *
>>> prop = Properties()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'Properties' is not defined
>>> from java.util import Properties
>>> prop = Properties()
>>> 

Windows

C:\jython2.7.3>java -jar jython.jar
Jython 2.7.3 (tags/v2.7.3:5f29801fe, Sep 10 2022, 18:52:49)
[Java HotSpot(TM) 64-Bit Server VM (Oracle Corporation)] on java1.8.0_371
Type "help", "copyright", "credits" or "license" for more information.
>>> from java.util import *
>>> prop = Properties()
>>>

[Keita2]

@jeff5 I also recreated on Windows.
On standalone release, this can be recreated.
Could you analyze why different behavior can be found ?

Stanalone

C:\temp>java -jar jython-standalone-2.7.2.jar
Jython 2.7.2 (v2.7.2:925a3cc3b49d, Mar 21 2020, 10:03:58)
[Java HotSpot(TM) 64-Bit Server VM (Oracle Corporation)] on java1.8.0_371
Type "help", "copyright", "credits" or "license" for more information.
>>> from java.util import *
>>> prop = Properties()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'Properties' is not defined
>>> from java.util import Properties
>>> prop = Properties()
>>> 

Installer

C:\jython2.7.2>java -jar jython.jar
Jython 2.7.2 (v2.7.2:925a3cc3b49d, Mar 21 2020, 10:03:58)
[Java HotSpot(TM) 64-Bit Server VM (Oracle Corporation)] on java1.8.0_371
Type "help", "copyright", "credits" or "license" for more information.
>>> from java.util import *
>>> prop = Properties()
>>> 

[Keita2]

Hello are there any updates ?

[ohumbel]

@jeff5 I also recreated on Windows. On standalone release, this can be recreated. Could you analyze why different behavior can be found ?

Standalone mode was deliberately designed to not support java imports of the form from a.package import *: Package scanning is disabled in standalone mode.

The reason for this are application containers like WildFly, Payara, Websphere and other more complex java applications. Each of those has its own layout and handling of the class path and class loaders. It would be impossible for jython to completely scan the whole class path for packages. And it would considerably slow down the startup process.

Hope to have helped to spot the difference.

[Stewori]

@ohumbel Thank you for the clarification. I was somewhat surprised by this limitation; looking at the Package Java API, indeed no method there can list the classes in a given package. Apparently, class loaders do not provide this functionality and workarounds are expensive.
In any case, Jython 2.x is not the place for revisiting established behavior and for Jython 3 there might not even be a standalone. So, we could perhaps look into improving the error message, i.e. ideally Jython would tell the user something like "Wildcard imports are not supported in the standalone build.". And it should be mentioned prominently on the user guide (I can't remember to have ever heard of this limitation; maybe I overlooked it).

[Keita2]

Is it correct that error message will be improved and user guide will be also updated ?

[Stewori]

No promise from my side, but I have loose plans to clean up the user guide and then I would include this bit. Fixing the error is rather low priority and everyone is busy :) However I think this issue will stay open until it is resolved eventually. If you want to make a PR, that would be very welcome. @jeff5: It would be good if you could confirm the resolution (i.e. via improving the error message)(, or suggest an alternative).

[jeff5]

I second Stefan's thanks @ohumbel, that's a really useful insight. And "standalone" was what I was missing earlier.

The way that Python packages differ from Java's concept is a continual source of surprises: superficially similar, then not quite the same thing. In some ways, Java's concept is more robust: it will look for what you explicitly request, and in as many remote corners as it has class loaders for, but it won't enumerate what is available.

Java packages are somewhat like Python namepace packages, in having multiple loci, but those are confined to the file system.

It is interesting to see what you can get from a star import:

PS 274b1-trial> java -jar kit\jython-standalone.jar
Jython 2.7.4b1 (tags/v2.7.4b1:228fe9ef9, Apr 1 2024, 20:04:13)
[Java HotSpot(TM) 64-Bit Server VM (Oracle Corporation)] on java11.0.22
Type "help", "copyright", "credits" or "license" for more information.
>>> globals().keys()
['__builtins__', '__doc__', '__name__', '__package__']
>>> from java.util import *
>>> globals().keys()
['Set', '__name__', '__builtins__', '__doc__', 'List', 'Collections', 'Map', '__package__', 'WeakHashMap']

I assume this is because some other code already imported those classes explicitly to Python's idea of java.util.

Star imports are discouraged in Python, and I wonder if they should not simply be an error when the package is a Java one. (Not in 2.7, probably.)

[Keita2]

@Stewori
Thank you for reply.
@jeff5
I am afraid, but so would you have a plan to fix the code so that not error but other kind of message is issued when the package is a Java one ?

[jeff5]

... so would you have a plan to fix the code so that not error but other kind of message is issued when the package is a Java one ?

Are you suggesting a warning in this case that an import * may not have imported everything in the Java package?

[Keita2]

Yes, I would like to make the request.

[yogi1967]

Very odd.. Import * Works for me on 2.7.2 (Java21) on Mac, but NOT on Windows....?