Doesn't that "just drop down to C" get complicated when you need to pass callback functions though? Users will want to write them in the original language for

Doesn't that "just drop down to C" get complicated when you need to pass callback functions though? Users will want to write them in the original language for convenience and to use closures safely and easily. Wouldn't that kill your performance if the callback function is just Python again but called many times (e.g. an integrand for a numeric integration function, which integrand depends on captured runtime params). This is no problem in Julia, what are people doing cases like this in Python land?