Print an error message without printing a traceback and close the program when a condition is not met

Question

I've seen similar questions to this one but none of them really address the trackback. If I have a class like so

class Stop_if_no_then():     def __init__(self, value one, operator, value_two, then, line_or_label, line_number):         self._firstvalue = value_one         self._secondvalue = value_two         self._operator = operator         self._gohere = line_or_label         self._then = then         self._line_number = line_number      def execute(self, OtherClass):         "code comparing the first two values and making changes etc" 

What I want my execute method to be able to do is if self._then is not equal to the string "THEN" (in allcaps) then I want it to raise a custom error message and terminate the whole program while also not showing a traceback.

If the error is encountered the only thing that should print out would look something like (I'm using 3 as an example, formatting is not a problem) this.

`Syntax Error (Line 3): No -THEN- present in the statement.` 

I'm not very picky about it actually being an exception class object, so there's no issue in that aspect. Since I will be using this in a while loop, simple if, elif just repeats the message over and over (because obviously I am not closing the loop). I have seen sys.exit() but that also prints out a giant block of red text, unless I am not using it correctly. I don't want to catch the exception in my loop because there are other classes in the same module in which I need to implement something like this.

Answer 1

You can turn off the traceback by limiting its depth.

Python 2.x

import sys sys.tracebacklimit = 0 

Python 3.x

In Python 3.5.2 and 3.6.1, setting tracebacklimit to 0 does not seem to have the intended effect. This is a known bug. Note that -1 doesn't work either. Setting it to None does however seem to work, at least for now.

In Python 3.6.2 and above you should set tracebacklimit to 0 or -1, as setting it to None does not disable the traceback output.

Python 3.6.1 and bellow results:

>>> import sys  >>> sys.tracebacklimit = 0 >>> raise Exception Traceback (most recent call last):   File "<stdin>", line 1, in <module> Exception  >>> sys.tracebacklimit = -1 >>> raise Exception Traceback (most recent call last):   File "<stdin>", line 1, in <module> Exception  >>> sys.tracebacklimit = None >>> raise Exception Exception 

Python 3.6.2 and above results:

>>> import sys  >>> sys.tracebacklimit = 0 >>> raise Exception Exception  >>> sys.tracebacklimit = -1 >>> raise Exception Exception  >>> sys.tracebacklimit = None >>> raise Exception Traceback (most recent call last):   File "<stdin>", line 1, in <module> Exception 

Nevertheless, for better or worse, if multiple exceptions are raised, they can all still be printed. For example:

socket.gaierror: [Errno -2] Name or service not known  During handling of the above exception, another exception occurred:  urllib.error.URLError: <urlopen error [Errno -2] Name or service not known>