PythonCall equivalent to PyCall's pytype_mapping?

In SymPy.jl there is use of PyCall's pytype_mapping to automatically convert sympy objects in Python into a typed object in Julia. It looks like in PythonCall, the pyconvert_add_rule does something similar, but I can’t seem to get it to work. I thought something like: PythonCall.pyconvert_add_rule("sympy.core.basic.Basic", Sym, (args...) -> print("hi"), 100) might show me what is needed to replace pytype_mapping(sympy_core.basic.Basic, Sym) but I’m pretty sure I’m am not specifying the first argument correctly (the underlying python type). Anyone able to offer guidance here?