Add simple example for PyArray<PyObject>. (#339)

Add simple example for PyArray<PyObject>.

Author: Chuxiaof

examples/simple/src/lib.rs

@@ -7,13 +7,21 @@ use numpy::{
     PyReadwriteArray1, PyReadwriteArrayDyn,
 };
 use pyo3::{
+    exceptions::PyIndexError,
     pymodule,
     types::{PyDict, PyModule},
-    FromPyObject, PyAny, PyResult, Python,
+    FromPyObject, PyAny, PyObject, PyResult, Python,
 };
 
 #[pymodule]
 fn rust_ext(_py: Python<'_>, m: &PyModule) -> PyResult<()> {
+    // example using generic PyObject
+    fn head(x: ArrayViewD<'_, PyObject>) -> PyResult<PyObject> {
+        x.get(0)
+            .cloned()
+            .ok_or_else(|| PyIndexError::new_err("array index out of range"))
+    }
+
     // example using immutable borrows producing a new array
     fn axpy(a: f64, x: ArrayViewD<'_, f64>, y: ArrayViewD<'_, f64>) -> ArrayD<f64> {
         a * &x + &y
@@ -34,6 +42,13 @@ fn rust_ext(_py: Python<'_>, m: &PyModule) -> PyResult<()> {
         &x + &y
     }
 
+    // wrapper of `head`
+    #[pyfn(m)]
+    #[pyo3(name = "head")]
+    fn head_py(_py: Python<'_>, x: PyReadonlyArrayDyn<'_, PyObject>) -> PyResult<PyObject> {
+        head(x.as_array())
+    }
+
     // wrapper of `axpy`
     #[pyfn(m)]
     #[pyo3(name = "axpy")]

examples/simple/tests/test_ext.py

@@ -1,5 +1,11 @@
 import numpy as np
-from rust_ext import axpy, conj, mult, extract, add_minutes_to_seconds, polymorphic_add
+from rust_ext import head, axpy, conj, mult, extract, add_minutes_to_seconds, polymorphic_add
+
+
+def test_head():
+    x = np.array(['first', None, 42])
+    first = head(x)
+    assert first == 'first'
 
 
 def test_axpy():