Puzzling error msg.

Steven D'Aprano steve+comp.lang.python at pearwood.info
Mon Dec 3 19:12:11 CET 2012

On Mon, 03 Dec 2012 12:37:42 -0500, wrw wrote:

> So far in my experience with Python, it's error messages have been
> clear, concise, and quite good at fingering my errors.  However, the
> message below has me stumped.  The routine in question has been running
> for weeks with no problems, then yesterday I got the following:
> Traceback (most recent call last):
>   File "./Connection_Monitor.py", line 146, in <module>
>     Google_up, Google_summary, Google_RTT, Google_stddev = 
>   File "/Users/wrw/Dev/Python/Connection_Monitor/Version2.2/WorkingCopy/
>   line 101, in connection_test
>     #
> IndexError: list index out of range

Are you running Python with the -x option? If so, then I understand that 
the line number (and subsequent line of code) reported in tracebacks may 
sometimes be off by one.

If not, or if the discrepancy is more than one line, I would start 
investigating the following scenario:

* there is a mismatch between the source code .py file and the 
  byte-code .pyc file;

* but the .pyc file's "last modified date" is newer than the .py file;

* the .pyc file is executed (as is usual);

* but when an error occurs and Python looks up the source file, it
  gets something which no longer corresponds to the byte-code being

By the way, in connection_test you have the following:

>     def connection_test(self):
>         found_0 = '0 packets received' in ping_result 
>         found_1 = '1 packets received' in ping_result
>         if found_0 == True or found_1 == True:

Of course that's not correct. You should write:

if (found_0 == True or found_1 == True) == True:

No wait, I mean:

if ((found_0 == True or found_1 == True) == True) == True:

No wait! I meant this:

if ((found_0 == True == True == True == True == ... # Help!
   or found_1 == True == True == True == True == ... # Where do I stop?
   ) == True) == True == True == True == True ... :


Of course the whole thing is silly. The right way to test booleans for 
their boolean value is just:

if found_0 or found_1:

"flag == True" is the same as "flag".


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