invoice() takes 0 positional arguments but 1 was given in python code example

Example: TypeError: takes 0 positional arguments but 1 was given python

When Python tells you "generatecode() takes 0 positional arguments but 1 was
given", it's telling you that your method is set up to take no arguments, but
the self argument is still being passed when the method is called, so in fact
it is receiving one argument.

Adding self to your method definition should resolve the problem.