Rule Definition
Care must be taken if completion of a try-catch block occurs as a result of executing a return. If a finally block also returns a value, then that return supersedes any previous return in the try-catch block. Also, if an exception was thrown in the try or catch blocks that was not caught, then execution of a return in the finally block prevents the exception from being thrown to the caller (because it is not possible for the caller to simultaneously evaluate the return and catch the exception). This is also valid for break or continue instructions.

Remediation
Avoid using finally statement in return block. If used, it will swallow the exception raised but not handled in above try except block.

Violation Code Sample

>>> def experiment():
>>>     try:
>>>         x = 2/0
>>>     except:
>>>         logging.debug("Not possible")
>>>     finally:
>>>         logging.debug("Division")
>>>         return

Fixed Code Sample

>>> def experiment():
>>>     try:
>>>         x = 2/0
>>>     except:
>>>         logging.debug("Not Possible")
>>>     finally:
>>>         logging.debug("Division")
>>>         clean_up_code()    #Return should not be used inside finally
        

CISQ OMG ASCMM-MNT-01