Redirect to file

[DeaD_EyE]

This happens, because you don't catch any exception while calling func().
You can catch all exceptions and log them to a file.
Instead of overwriting sys.stdout, use the print function.
You can define with file the outputfile which is print using.

def decorator(func):
    def wrapper():
        with open('output', 'w') as fd:
            try:
                result = func()
            except Exception as error:
                print(error, file=fd)
            else:
                print(result, file=fd) 
    return wrapper

To return a value, you have to add after the print in the else block return result