Function warn_explicit 

pub fn warn_explicit(
    category: Option<PyTypeRef>,
    message: PyObjectRef,
    filename: PyStrRef,
    lineno: usize,
    module: Option<PyObjectRef>,
    registry: PyObjectRef,
    source_line: Option<PyObjectRef>,
    source: Option<PyObjectRef>,
    vm: &VirtualMachine,
) -> PyResult<()>

Core warning logic matching warn_explicit() in _warnings.c.