@@ -154,6 +154,7 @@ namespace xt
         using inner_shape_type = typename base_type::inner_shape_type;
         using inner_strides_type = typename base_type::inner_strides_type;
         using inner_backstrides_type = typename base_type::inner_backstrides_type;
+        constexpr static std::size_t rank = SIZE_MAX;
 
         pyarray();
         pyarray(const value_type& t);
@@ -514,7 +515,7 @@ namespace xt
         {
             return;
         }
-        
+
         m_shape = inner_shape_type(reinterpret_cast<size_type*>(PyArray_SHAPE(this->python_array())),
                                    static_cast<size_type>(PyArray_NDIM(this->python_array())));
         m_strides = inner_strides_type(reinterpret_cast<difference_type*>(PyArray_STRIDES(this->python_array())),
 
@@ -164,6 +164,7 @@ namespace xt
         using inner_shape_type = typename base_type::inner_shape_type;
         using inner_strides_type = typename base_type::inner_strides_type;
         using inner_backstrides_type = typename base_type::inner_backstrides_type;
+        constexpr static std::size_t rank = N;
 
         pytensor();
         pytensor(nested_initializer_list_t<T, N> t);
@@ -467,7 +468,7 @@ namespace xt
         {
             return;
         }
-        
+
         if (PyArray_NDIM(this->python_array()) != N)
         {
             throw std::runtime_error("NumPy: ndarray has incorrect number of dimensions");
 
@@ -89,6 +89,7 @@ set(XTENSOR_PYTHON_TESTS
     test_pyarray_traits.cpp
     test_pytensor.cpp
     test_pyvectorize.cpp
+    test_sfinae.cpp
 )
 
 add_executable(test_xtensor_python ${XTENSOR_PYTHON_TESTS} ${XTENSOR_PYTHON_HEADERS})
 
@@ -0,0 +1,53 @@
+/***************************************************************************
+* Copyright (c) Wolf Vollprecht, Johan Mabille and Sylvain Corlay          *
+* Copyright (c) QuantStack                                                 *
+*                                                                          *
+* Distributed under the terms of the BSD 3-Clause License.                 *
+*                                                                          *
+* The full license is in the file LICENSE, distributed with this software. *
+****************************************************************************/
+
+#include <limits>
+
+#include "gtest/gtest.h"
+#include "xtensor-python/pytensor.hpp"
+#include "xtensor-python/pyarray.hpp"
+#include "xtensor/xarray.hpp"
+#include "xtensor/xtensor.hpp"
+
+namespace xt
+{
+    template <class E, std::enable_if_t<!xt::has_fixed_rank_t<E>::value, int> = 0>
+    inline bool sfinae_has_fixed_rank(E&&)
+    {
+        return false;
+    }
+
+    template <class E, std::enable_if_t<xt::has_fixed_rank_t<E>::value, int> = 0>
+    inline bool sfinae_has_fixed_rank(E&&)
+    {
+        return true;
+    }
+
+    TEST(sfinae, fixed_rank)
+    {
+        xt::pyarray<size_t> a = {{9, 9, 9}, {9, 9, 9}};
+        xt::pytensor<size_t, 1> b = {9, 9};
+        xt::pytensor<size_t, 2> c = {{9, 9}, {9, 9}};
+
+        EXPECT_TRUE(sfinae_has_fixed_rank(a) == false);
+        EXPECT_TRUE(sfinae_has_fixed_rank(b) == true);
+        EXPECT_TRUE(sfinae_has_fixed_rank(c) == true);
+    }
+
+    TEST(sfinae, get_rank)
+    {
+        xt::pytensor<double, 1> A = xt::zeros<double>({2});
+        xt::pytensor<double, 2> B = xt::zeros<double>({2, 2});
+        xt::pyarray<double> C = xt::zeros<double>({2, 2});
+
+        EXPECT_TRUE(xt::get_rank<decltype(A)>::value == 1ul);
+        EXPECT_TRUE(xt::get_rank<decltype(B)>::value == 2ul);
+        EXPECT_TRUE(xt::get_rank<decltype(C)>::value == SIZE_MAX);
+    }
+}
Original file line number	Diff line number	Diff line change
@@ -164,6 +164,7 @@ namespace xt
164	164	using inner_shape_type = typename base_type::inner_shape_type;
165	165	using inner_strides_type = typename base_type::inner_strides_type;
166	166	using inner_backstrides_type = typename base_type::inner_backstrides_type;
	167	+ constexpr static std::size_t rank = N;
167	168
168	169	pytensor();
169	170	pytensor(nested_initializer_list_t<T, N> t);
@@ -467,7 +468,7 @@ namespace xt
467	468	{
468	469	return;
469	470	}
470		-
	471	+
471	472	if (PyArray_NDIM(this->python_array()) != N)
472	473	{
473	474	throw std::runtime_error("NumPy: ndarray has incorrect number of dimensions");
Original file line number	Diff line number	Diff line change
@@ -89,6 +89,7 @@ set(XTENSOR_PYTHON_TESTS
89	89	test_pyarray_traits.cpp
90	90	test_pytensor.cpp
91	91	test_pyvectorize.cpp
	92	+ test_sfinae.cpp
92	93	)
93	94
94	95	add_executable(test_xtensor_python ${XTENSOR_PYTHON_TESTS} ${XTENSOR_PYTHON_HEADERS})