Matching Python 2 int behavior on Python 2

Author: henryiii

include/pybind11/cast.h

@@ -980,11 +980,19 @@ struct type_caster<T, enable_if_t<std::is_arithmetic<T>::value && !is_std_char_t
     static handle cast(T src, return_value_policy /* policy */, handle /* parent */) {
         if (std::is_floating_point<T>::value) {
             return PyFloat_FromDouble((double) src);
-        } else if (sizeof(T) <= sizeof(long)) {
+        } else if (sizeof(T) <= sizeof(ssize_t)) {
+#if PY_VERSION_HEX < 0x03000000
+            // This returns a long automatically if needed
             if (std::is_signed<T>::value)
-                return PyLong_FromLong((long) src);
+                return PyInt_FromSsize_t((ssize_t) src);
             else
-                return PyLong_FromUnsignedLong((unsigned long) src);
+                return PyInt_FromSize_t((size_t) src);
+#else
+            if (std::is_signed<T>::value)
+                return PyLong_FromSsize_t((ssize_t) src);
+            else
+                return PyLong_FromSize_t((size_t) src);
+#endif
         } else {
             if (std::is_signed<T>::value)
                 return PyLong_FromLongLong((long long) src);

tests/test_builtin_casters.cpp

@@ -155,4 +155,9 @@ TEST_SUBMODULE(builtin_casters, m) {
     // test_complex
     m.def("complex_cast", [](float x) { return "{}"_s.format(x); });
     m.def("complex_cast", [](std::complex<float> x) { return "({}, {})"_s.format(x.real(), x.imag()); });
+
+    // test int vs. long (Python 2)
+    m.def("int_cast", [](){return (int) 42;});
+    m.def("long_cast", [](){return (long) 42;});
+    m.def("longlong_cast", [](){return (long long) 42;});
 }

tests/test_builtin_casters.py

@@ -323,3 +323,9 @@ def test_numpy_bool():
     assert convert(np.bool_(False)) is False
     assert noconvert(np.bool_(True)) is True
     assert noconvert(np.bool_(False)) is False
+
+def test_int_long():
+    import sys
+    type(m.int_cast()) == type(1)
+    type(m.long_cast()) == type(1)
+    type(m.longlong_cast()) == type(sys.maxint + 1)