Function defaulter_from_decoder 

pub fn defaulter_from_decoder(decoder: &str) -> String

The defaulter that goes with a decoder, by name.

The two schemes differ in one word — zd_dec_p_long against zd_def_p_long — because both are built from the same key. Doing it by text lets crate::emit::python::Python name the defaulter from a routine that has only a signature; a name that does not resolve is a NameError naming the function.