nicer error message for invalid function arguments

include/pybind11/pybind11.h

@@ -460,8 +460,10 @@ protected:
             if (overloads->is_operator)
                 return handle(Py_NotImplemented).inc_ref().ptr();
 
-            std::string msg = "Incompatible " + std::string(overloads->is_constructor ? "constructor" : "function") +
+            std::string msg = std::string(overloads->name) + "(): incompatible " +
-                              " arguments. The following argument types are supported:\n";
+                std::string(overloads->is_constructor ? "constructor" : "function") +
+                " arguments. The following argument types are supported:\n";
+
             int ctr = 0;
             for (detail::function_record *it2 = overloads; it2 != nullptr; it2 = it2->next) {
                 msg += "    "+ std::to_string(++ctr) + ". ";
@@ -489,7 +491,7 @@ protected:
 
                 msg += "\n";
             }
-            msg += "    Invoked with: ";
+            msg += "\nInvoked with: ";
             tuple args_(args, true);
             for (size_t ti = overloads->is_constructor ? 1 : 0; ti < args_.size(); ++ti) {
                 msg += static_cast<std::string>(static_cast<object>(args_[ti]).str());

tests/test_callbacks.py

@@ -83,7 +83,7 @@ def test_cpp_function_roundtrip():
 
     with pytest.raises(TypeError) as excinfo:
         test_dummy_function(dummy_function2)
-    assert "Incompatible function arguments" in str(excinfo.value)
+    assert "incompatible function arguments" in str(excinfo.value)
 
     with pytest.raises(TypeError) as excinfo:
         test_dummy_function(lambda x, y: x + y)

tests/test_inheritance.py

@@ -24,9 +24,10 @@ def test_inheritance(msg):
     with pytest.raises(TypeError) as excinfo:
         dog_bark(polly)
     assert msg(excinfo.value) == """
-        Incompatible function arguments. The following argument types are supported:
+        dog_bark(): incompatible function arguments. The following argument types are supported:
             1. (arg0: m.Dog) -> str
-            Invoked with: <m.Pet object at 0>
+
+        Invoked with: <m.Pet object at 0>
     """
 
 

tests/test_issues.py

@@ -65,17 +65,19 @@ def test_no_id(capture, msg):
     with pytest.raises(TypeError) as excinfo:
         get_element(None)
     assert msg(excinfo.value) == """
-        Incompatible function arguments. The following argument types are supported:
+        get_element(): incompatible function arguments. The following argument types are supported:
             1. (arg0: m.issues.ElementA) -> int
-            Invoked with: None
+
+        Invoked with: None
     """
 
     with pytest.raises(TypeError) as excinfo:
         expect_int(5.2)
     assert msg(excinfo.value) == """
-        Incompatible function arguments. The following argument types are supported:
+        expect_int(): incompatible function arguments. The following argument types are supported:
             1. (arg0: int) -> int
-            Invoked with: 5.2
+
+        Invoked with: 5.2
     """
     assert expect_float(12) == 12
 
@@ -90,10 +92,11 @@ def test_str_issue(msg):
     with pytest.raises(TypeError) as excinfo:
         str(StrIssue("no", "such", "constructor"))
     assert msg(excinfo.value) == """
-        Incompatible constructor arguments. The following argument types are supported:
+        __init__(): incompatible constructor arguments. The following argument types are supported:
             1. m.issues.StrIssue(arg0: int)
             2. m.issues.StrIssue()
-            Invoked with: no, such, constructor
+
+        Invoked with: no, such, constructor
     """
 
 

tests/test_kwargs_and_defaults.py

@@ -35,9 +35,10 @@ def test_named_arguments(msg):
         # noinspection PyArgumentList
         kw_func2(x=5, y=10, z=12)
     assert msg(excinfo.value) == """
-        Incompatible function arguments. The following argument types are supported:
+        kw_func2(): incompatible function arguments. The following argument types are supported:
             1. (x: int=100, y: int=200) -> str
-            Invoked with:
+
+        Invoked with:
     """
 
     assert kw_func4() == "{13 17}"

tests/test_opaque_types.py

@@ -35,9 +35,10 @@ def test_pointers(msg):
     with pytest.raises(TypeError) as excinfo:
         get_void_ptr_value([1, 2, 3])  # This should not work
     assert msg(excinfo.value) == """
-        Incompatible function arguments. The following argument types are supported:
+        get_void_ptr_value(): incompatible function arguments. The following argument types are supported:
             1. (arg0: capsule) -> int
-            Invoked with: [1, 2, 3]
+
+        Invoked with: [1, 2, 3]
     """
 
     assert return_null_str() is None