adding isinstance<str> specialization to match native behavior, fixing up tests

Author: rwgk

include/pybind11/pytypes.h

@@ -950,6 +950,8 @@ inline namespace literals {
 inline str operator"" _s(const char *s, size_t size) { return {s, size}; }
 }
 
+template <> inline bool isinstance<str>(handle obj) { return PyUnicode_Check(obj.ptr()); }
+
 /// \addtogroup pytypes
 /// @{
 class bytes : public object {
@@ -1012,6 +1014,12 @@ inline str::str(const bytes& b) {
     m_ptr = obj.release().ptr();
 }
 
+#if PY_MAJOR_VERSION < 3
+using native_str = bytes;
+#else
+using native_str = str;
+#endif
+
 /// \addtogroup pytypes
 /// @{
 class none : public object {

include/pybind11/stl.h

@@ -144,7 +144,7 @@ template <typename Type, typename Value> struct list_caster {
     using value_conv = make_caster<Value>;
 
     bool load(handle src, bool convert) {
-        if (!isinstance<sequence>(src) || isinstance<str>(src))
+        if (!isinstance<sequence>(src) || isinstance<str>(src) || isinstance<native_str>(src))
             return false;
         auto s = reinterpret_borrow<sequence>(src);
         value.clear();

tests/test_eval.py

@@ -18,6 +18,8 @@ def test_evals(capture):
 @pytest.unsupported_on_pypy3
 def test_eval_file():
     filename = os.path.join(os.path.dirname(__file__), "test_eval_call.py")
+    if isinstance(filename, bytes):  # true for Python 2 only
+        filename = filename.decode()  # effectively six.ensure_text()
     assert m.test_eval_file(filename)
 
     assert m.test_eval_file_failure()

tests/test_pytypes.py

@@ -367,7 +367,7 @@ def test_isinstance_string_types():
     # pybind11 isinstance
     assert m.isinstance_pybind11_bytes(actual_bytes)
     assert not m.isinstance_pybind11_bytes(actual_unicode)
-    assert m.isinstance_pybind11_unicode(actual_bytes)  # NOT like native
+    assert not m.isinstance_pybind11_unicode(actual_bytes)
     assert m.isinstance_pybind11_unicode(actual_unicode)
 
 
@@ -379,7 +379,8 @@ def test_pass_actual_bytes_or_unicode_to_string_types():
     with pytest.raises(TypeError):
         m.pass_to_pybind11_bytes(actual_unicode)  # NO implicit encode
 
-    assert m.pass_to_pybind11_unicode(actual_bytes) == 5  # implicit decode
+    with pytest.raises(TypeError):
+        m.pass_to_pybind11_unicode(actual_bytes)  # NO implicit decode
     assert m.pass_to_pybind11_unicode(actual_unicode) == 3
 
     assert m.pass_to_std_string(actual_bytes) == 5