Debugging Error 999998 in ArcPy?

Question

I found an RuntimeError: ERROR 999998: Unexpected Error when lunching Arcpy in my ArcGis 10.1 such as this:

Runtime error 
Traceback (most recent call last):
  File "", line 50, in 
  File "c:\program files (x86)\arcgis\desktop10.1\arcpy\arcpy\sa\Functions.py", line 3840, in Minus
    in_raster_or_constant2)
  File "c:\program files (x86)\arcgis\desktop10.1\arcpy\arcpy\sa\Utils.py", line 47, in swapper
    result = wrapper(*args, **kwargs)
  File "c:\program files (x86)\arcgis\desktop10.1\arcpy\arcpy\sa\Functions.py", line 3837, in wrapper
    return _wrapLocalFunctionRaster(u"Minus_sa", ["Minus", in_raster_or_constant1, in_raster_or_constant2])
RuntimeError: ERROR 999998: Unexpected Error.

I've extensively gone through forums and found similar problems, but nothing proposed has resolved this problem. I haven't tried to reinstall ArcGIS, though.

My code is:

Also, when I execute the code, it gives OK until the Print "Ok1", which means that transmissionCapacity = Minus(tc1, losses) is not executed. Error 999998 worries me a lot.

Answer 1

You might be having a problem related to memory, which is why that error is being thrown.
Here is a help article that discusses Foreground vs Background processing. It directly references the error that you are receiving and relates it to running out of System memory.

Foreground and Background Processing

Taking a quick look at your python script, you are running 9 raster operations in your script before you reach Line 42. I am not sure whether you are running this from the Python window in ArcGIS, or if you are running it from an external IDE. I think the issue might arise regardless though. I know that in other programming I have done, the software does not empty memory out between functions. It basically keeps working in the same memory space until the entire script is completed. This could mean that each time you are running one of the Spatial Analyst functions, the raster is loaded into memory, and then kept there when it is finished and has moved on. Depending on the size of your raster, you could be filling up your entire memory allocation and the Minus function at Line 42 happens to be the one that fills up your memory mid-stream and causes the crash.

I am not enough of a python or arcpy guru to be able to say whether this is actually the case. There may be ways of forcing the memory to flush mid-script. Here are a couple of options that may help:

• Clear your variables as you are finished with them.
• Write some of these intermediate rasters to disk instead of keeping them in memory the entire time.
• Split your script up into parts and run it in two or more sections. This would let you clear out the ram more often.

This Stackoverflow entry discusses freeing memory in Python: How can I explicitly free memory in Python?
Also, doing a search at the Python website is always a good idea.

Hope this helps.

Answer 2

Errors should be analysed with Event Log Explorer to permanently get rid of the problem otherwise it keeps on reoccurring. Sometimes the previous logs should be analysed properly as they are the root cause of the real error. Check this for Windows Error log Analysis http://eventlogxp.com/blog/troubleshooting-philosophy-windows-event-log-error-analysis/