nwdiag packet diagram issues

[hla]

Hi,

I would like to create packet diagrams using nwdiag. I installed nwdiag version 1.04. running 

$ sudo pip3 install nwdiag

on my Ubuntu system. I created a test file example.diag:

packetdiag {

   0-7: Source Port

   8-15: Destination Port

}

and tried to generate a packed diagram from it, running

$ nwdiag --debug example.diag

However, I am getting the following error message:

Traceback (most recent call last):

  File "/usr/local/lib/python3.6/dist-packages/nwdiag/parser.py", line 289, in parse_string

    tree = parse(tokenize(string))

  File "/usr/local/lib/python3.6/dist-packages/nwdiag/parser.py", line 80, in tokenize

    return [x for x in t(string) if x.type not in useless]

  File "/usr/local/lib/python3.6/dist-packages/nwdiag/parser.py", line 80, in <listcomp>

    return [x for x in t(string) if x.type not in useless]

  File "/usr/local/lib/python3.6/dist-packages/funcparserlib/lexer.py", line 107, in f

    t = match_specs(compiled, str, i, (line, pos))

  File "/usr/local/lib/python3.6/dist-packages/funcparserlib/lexer.py", line 100, in match_specs

    raise LexerError((line, pos + 1), errline)

funcparserlib.lexer.LexerError: cannot tokenize data: 2,5: "   0-7: Source Port"

During handling of the above exception, another exception occurred:

Traceback (most recent call last):

  File "/usr/local/lib/python3.6/dist-packages/blockdiag/utils/bootstrap.py", line 53, in run

    parsed = self.parse_diagram()

  File "/usr/local/lib/python3.6/dist-packages/blockdiag/utils/bootstrap.py", line 87, in parse_diagram

    return self.module.parser.parse_string(self.code)

  File "/usr/local/lib/python3.6/dist-packages/nwdiag/parser.py", line 293, in parse_string

    raise ParseException(message)

nwdiag.parser.ParseException: Got unexpected token at line 2 column 5

has anyone encouter a similar issue and knows how to fix this?

Best,

Oliver