@abarnert You really saved my day. I have encountered the same problem as OP posted. The jython code is as following:
################################################################
# CONFIG DEFINITIONS
################################################################
#GOOD_IMAGE_URL = "http://192.168.1.15/11111111.png"
BAD_IMAGE_URL = "http://192.168.1.15/111111112222.png"
def exceptionDemo(urlPath):
try:
print "exceptionDemo is starting"
myImg = imageio.ImageIO.read(URL(urlPath))
if myImg is None:
print "Img is None"
else:
print "Img is OK"
return myImg
#except Exception, err:
except java.lang.Exception as err:
print "Exception is here"
print err
finally:
print "Finally is here"
the purpose of this code is to download the image file specified by urlPath. when the ulrPath is bad(in this case, the 111111112222.png does not exist.), I would like to catch the exception in order to handle this issue properly.
If I simply use the normal "except Exception, err" to catch the exception, the program will just abort without any information. The print statements in except and finally section are supposed to execute, however, that didn't happen. What I get is nothing after seeing "exceptionDemo is starting".
I spent days on dealing with this problem, searching on google again and again, leaving no stone unturned. After days of investigation, I get the idea that there are two sorts of exceptions when you programming in jython, one is python exception, the other is java exception. The reason for this problem is that either jython or SikuliX in this case, has suppressed the java throwables. I am not very familiar with jython, so it's just my guess and it has not been verified(I am more familiar with native Python and Java).
At first, I doubt it's ImageIO - the native java package's problem. I wrote a simple java demo to test ImageIO by giving the bad image url, it worked great, a nice "javax.imageio.IIOException: Can't get input stream from URL" had been thrown out. Then, I know that my guess is right. The java exception somehow did not well handled in jython or SikuliX. The point here is that even if this is the root cause, I still need a simple and elegent way to deal with this problem. I tried some other workarounds, but nothing is as good as I've expected. The essential part of this problem is not about downloading the image, it's about catching the exception.
It was not until I simply replace "except Exception, err“ with "except java.lang.Exception as err" that the code is working like a charm. I got all the printouts that I expected.
Your posts really saved my day. Good job and many thanks.
The following references are very helpful in my investigation:
javax.ImageIO methods fail silently
trap exceptions comprehensively in Jython
https://www.jython.org/jythonbook/en/1.0/ExceptionHandlingDebug.html
Finally, If there were any tips I would like to offer to people who find this post, it should be "STAY AWAY FROM THIS KIND OF HALF-BAKED SHODDY HYBRID LANGUAGE", You will get neither the expediency of Python, nor the robustness of Java, the only thing that you eventually will get is a big waste of your time.
=================================================================
Update on 2019-08-02:
As a follow-up of this post, I offer you a "buy one get more free" deal. It contains a heck of surprise brought you by Jython and Sikuli X.
1, DO NOT USE ANYTHING DEPENDS ON Netty in Jython. This includes httplib and urllib2, etc. It will fail if you try to GET/POST something in a loop, use Requests or java.net instead.
for details, please refer to this post: Why does this Jython loop fail after a single run?
2, DO NOT USE type() function in Sikuli X. This function is normally used in python to determine the type of an object, however, Sikuli X use it to mimic the keyboard input function. If you insist, you should import builtin first, then call it like this:
# -*- encoding: utf-8 -*-
import __builtin__
if __name__ == '__main__':
a=10
print __builtin__.type(a)
for details, please refer to these:
How to check variable type using “type” function in Sikuli
https://answers.launchpad.net/sikuli/+question/239574
These are some pitfalls that I have experienced in jython and Sikuli X, if you have to work with these two things, good luck and wish you have fun.
