Ways to define tokens seems to have different effects. about ply

[helpermethod]

This works as expected and is covered in the documentation

(i.e., functions are matched in order of specification whereas strings are sorted by regular expression length).

This is why in your first example this is matched by t_ANYTHING (its regular is expression is longer than that of t_THIS.

In the second example t_THIS(t) comes before t_ANYTHING(t), so matches first.