[Pyparsing] Forward() causing odd behaviour

[cathal c. <cof...@gm...>]

Hi everyone,

I have found something very weird. When I type the below into my
python console I get the following error: ParseException: Expected ")"
(at char 3), (line:1, col:4)

from pyparsing import *
function = Forward()
function = '#' + Word(nums) + Group(Literal('(') + Optional(function))
+ Literal(')')
function.parseString('#0(#1())', True)

However, if I then re-enter everything accept the line: function = Forward()
it works as I initially expected it to.

from pyparsing import *
function = '#' + Word(nums) + Group(Literal('(') + Optional(function))
+ Literal(')')
function.parseString('#0(#1())', True)
Out[6]: (['#', '0', (['(', '#', '1', (['('], {}), ')'], {}), ')'], {})

How do I make this work without having to enter the first sequence and
then the second sequence of modified statements?

Kind regards,
Cathal