Bool conversion: simplifications and comments

pybind · Jul 23, 2017 · 9b4f569 · 9b4f569
1 parent 15c3000
commit 9b4f569
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Showing 2 changed files with 17 additions and 18 deletions.
diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
@@ -1054,29 +1054,26 @@ template <> class type_caster<bool> {
         else if (src.ptr() == Py_True) { value = true; return true; }
         else if (src.ptr() == Py_False) { value = false; return true; }
         else if (convert) {
-            // This is quite similar to PyObject_IsTrue(), but it doesn't default
-            // to "True" for arbitrary objects.
             Py_ssize_t res = -1;
             if (src.is_none()) {
-                res = 0;
+                res = 0;  // None is implicitly converted to False
             }
-            #if !defined(PYPY_VERSION)
-            #if PY_MAJOR_VERSION >= 3
-            else if (src.ptr()->ob_type->tp_as_number && src.ptr()->ob_type->tp_as_number->nb_bool) {
-                res = (*src.ptr()->ob_type->tp_as_number->nb_bool)(src.ptr());
-            }
-            #else
-            else if (src.ptr()->ob_type->tp_as_number && src.ptr()->ob_type->tp_as_number->nb_nonzero) {
-                res = (*src.ptr()->ob_type->tp_as_number->nb_nonzero)(src.ptr());
+            #if defined(PYPY_VERSION)
+            // On PyPy, check that "__bool__" (or "__nonzero__" on Python 2.7) attr exists
+            else if (hasattr(src, PYBIND11_BOOL_ATTR)) {
+                res = PyObject_IsTrue(src.ptr());
             }
-            #endif
             #else
-            if (hasattr(src, PYBIND11_NONZERO)) {
-                res = PyObject_IsTrue(src.ptr());
+            // Alternate approach for CPython: this does the same as the above, but optimized
+            // using the CPython API so as to avoid an unneeded attribute lookup.
+            else if (auto tp_as_number = src.ptr()->ob_type->tp_as_number) {
+                if (PYBIND11_NB_BOOL(tp_as_number)) {
+                    res = (*PYBIND11_NB_BOOL(tp_as_number))(src.ptr());
+                }
             }
             #endif
-            if (res >= 0) {
-                value = res != 0;
+            if (res == 0 || res == 1) {
+                value = (bool) res;
                 return true;
             }
             return false;

diff --git a/include/pybind11/common.h b/include/pybind11/common.h
@@ -152,7 +152,8 @@
 #define PYBIND11_SLICE_OBJECT PyObject
 #define PYBIND11_FROM_STRING PyUnicode_FromString
 #define PYBIND11_STR_TYPE ::pybind11::str
-#define PYBIND11_NONZERO "__bool__"
+#define PYBIND11_BOOL_ATTR "__bool__"
+#define PYBIND11_NB_BOOL(ptr) ((ptr)->nb_bool)
 #define PYBIND11_PLUGIN_IMPL(name) \
     extern "C" PYBIND11_EXPORT PyObject *PyInit_##name()
 
@@ -173,7 +174,8 @@
 #define PYBIND11_SLICE_OBJECT PySliceObject
 #define PYBIND11_FROM_STRING PyString_FromString
 #define PYBIND11_STR_TYPE ::pybind11::bytes
-#define PYBIND11_NONZERO "__nonzero__"
+#define PYBIND11_BOOL_ATTR "__nonzero__"
+#define PYBIND11_NB_BOOL(ptr) ((ptr)->nb_nonzero)
 #define PYBIND11_PLUGIN_IMPL(name) \
     static PyObject *pybind11_init_wrapper();               \
     extern "C" PYBIND11_EXPORT void init##name() {          \