get_stack() will get you all the information you need in regards to the call stack. This function was intended for debugging. A function should not rely on knowing who calls it to execute.
If you are wanting to do some setup when called from
_ready() but not when called from
_process() there are much better ways:
my_member_variable = ["foo", "bar"]
var a = my_member_variable + " now i'm doing the rest"
var bar = my_member_variable
my_member_variable = ["bar", "baz"]
if not my_cool_variable:
my_cool_variable = "is now setup"
var i = "now i'm doing the rest" + my_cool_variable