How do I use a macro defined in another crate?

问题

I've seen a couple tutorials to create a Python module using the cpython crate but still have errors when building:

extern crate cpython;

use cpython::{PyObject, PyResult, Python, PyTuple, PyDict, ToPyObject, PythonObject};

fn add_two(py: Python, args: &PyTuple, _: Option<&PyDict>) -> PyResult<PyObject> {
    match args.as_slice() {
        [ref a_obj, ref b_obj] => {
            let a = a_obj.extract::<i32>(py).unwrap();
            let b = b_obj.extract::<i32>(py).unwrap();
            let mut acc:i32 = 0;

            for _ in 0..1000 {
                acc += a + b;
            }

            Ok(acc.to_py_object(py).into_object())
        },
        _ => Ok(py.None())
    }
}

py_module_initializer!(example, |py, module| {
    try!(module.add(py, "add_two", py_fn!(add_two)));
    Ok(())
});

I get:

error: macro undefined: 'py_module_initializer!'

Where do I get it? I am using Rust 1.12.

---

UPD

1. Need to add #[macro_use] (as in answers)
2. For other errors - see examples here

回答1:

You probably need to declare cpython as follows:

#[macro_use] extern crate cpython;

To be able to use cpython's macros. You can consult the example in its docs.

回答2:

You must add the #[macro_use] attribute on the extern crate declaration to ask the compiler to bring the macros exported by the crate into your crate's namespace.

#[macro_use]
extern crate cpython;

来源：https://stackoverflow.com/questions/39945901/how-do-i-use-a-macro-defined-in-another-crate