Question

Here is the simple code:

import sys

class EmptyArgs(StandardError):
    pass

if __name__ == "__main__":
    # The first way to raise an exception
    if len(sys.argv) == 1:
       raise EmptyArgs
    # The second way to raise an exception
    if len(sys.argv) == 1:
       raise EmptyArgs()

Which way is "more" correct? Both are working.
Note: In my real code, the exception is exactly the same as I declared: without a message and arguments.

Answer 1

Both are proper; the latter form lets you attach arguments to your exception:

if len(sys.argv) == 1:
   raise EmptyArgs('Specify at least 1 argument')

See the documentation for the raise statement

Python 2 had a few more options, these have been dropped from Python 3, where you could pass the exception class and arguments as a tuple, but Python 2 is now long gone.