Improve py::array_t scalar type information (#724)

* Add value_type member alias to py::array_t (resolve #632)

* Use numpy scalar name in py::array_t function signatures (e.g. float32/64 instead of just float)

include/pybind11/numpy.h

@@ -577,6 +577,8 @@ protected:
 
 template <typename T, int ExtraFlags = array::forcecast> class array_t : public array {
 public:
+    using value_type = T;
+
     array_t() : array(0, static_cast<const T *>(nullptr)) {}
     array_t(handle h, borrowed_t) : array(h, borrowed) { }
     array_t(handle h, stolen_t) : array(h, stolen) { }
@@ -822,7 +824,7 @@ inline PYBIND11_NOINLINE void register_structured_dtype(
 template <typename T, typename SFINAE> struct npy_format_descriptor {
     static_assert(is_pod_struct<T>::value, "Attempt to use a non-POD or unimplemented POD type as a numpy dtype");
 
-    static PYBIND11_DESCR name() { return _("struct"); }
+    static PYBIND11_DESCR name() { return make_caster<T>::name(); }
 
     static pybind11::dtype dtype() {
         return reinterpret_borrow<pybind11::dtype>(dtype_ptr());
@@ -1140,7 +1142,9 @@ struct vectorize_helper {
 };
 
 template <typename T, int Flags> struct handle_type_name<array_t<T, Flags>> {
-    static PYBIND11_DESCR name() { return _("numpy.ndarray[") + make_caster<T>::name() + _("]"); }
+    static PYBIND11_DESCR name() {
+        return _("numpy.ndarray[") + npy_format_descriptor<T>::name() + _("]");
+    }
 };
 
 NAMESPACE_END(detail)

tests/test_numpy_array.cpp

@@ -17,6 +17,7 @@
 
 using arr = py::array;
 using arr_t = py::array_t<uint16_t, 0>;
+static_assert(std::is_same<arr_t::value_type, uint16_t>::value, "");
 
 template<typename... Ix> arr data(const arr& a, Ix... index) {
     return arr(a.nbytes() - a.offset_at(index...), (const uint8_t *) a.data(index...));

tests/test_numpy_array.py

@@ -279,6 +279,21 @@ def test_overload_resolution(msg):
     # No exact match, should call first convertible version:
     assert overloaded(np.array([1], dtype='uint8')) == 'double'
 
+    with pytest.raises(TypeError) as excinfo:
+        overloaded("not an array")
+    assert msg(excinfo.value) == """
+        overloaded(): incompatible function arguments. The following argument types are supported:
+            1. (arg0: numpy.ndarray[float64]) -> str
+            2. (arg0: numpy.ndarray[float32]) -> str
+            3. (arg0: numpy.ndarray[int32]) -> str
+            4. (arg0: numpy.ndarray[uint16]) -> str
+            5. (arg0: numpy.ndarray[int64]) -> str
+            6. (arg0: numpy.ndarray[complex128]) -> str
+            7. (arg0: numpy.ndarray[complex64]) -> str
+
+        Invoked with: 'not an array'
+    """
+
     assert overloaded2(np.array([1], dtype='float64')) == 'double'
     assert overloaded2(np.array([1], dtype='float32')) == 'float'
     assert overloaded2(np.array([1], dtype='complex64')) == 'float complex'
@@ -289,8 +304,8 @@ def test_overload_resolution(msg):
     assert overloaded3(np.array([1], dtype='intc')) == 'int'
     expected_exc = """
         overloaded3(): incompatible function arguments. The following argument types are supported:
-            1. (arg0: numpy.ndarray[int]) -> str
+            1. (arg0: numpy.ndarray[int32]) -> str
-            2. (arg0: numpy.ndarray[float]) -> str
+            2. (arg0: numpy.ndarray[float64]) -> str
 
         Invoked with:"""
 

tests/test_numpy_vectorize.py

@@ -71,5 +71,5 @@ def test_docs(doc):
     from pybind11_tests import vectorized_func
 
     assert doc(vectorized_func) == """
-        vectorized_func(arg0: numpy.ndarray[int], arg1: numpy.ndarray[float], arg2: numpy.ndarray[float]) -> object
+        vectorized_func(arg0: numpy.ndarray[int32], arg1: numpy.ndarray[float32], arg2: numpy.ndarray[float64]) -> object
     """  # noqa: E501 line too long