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Improve make_tuple error message under debugging

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When make_tuple fails (for example, when print() is called with a
non-convertible argument, as in #778) the error message a less helpful
than it could be:

    make_tuple(): unable to convert arguments of types 'std::tuple<type1, type2>' to Python object

There is no actual std::tuple involved (only a parameter pack and a
Python tuple), but it also doesn't immediately reveal which type caused
the problem.

This commit changes the debugging mode output to show just the
problematic type:

    make_tuple(): unable to convert argument of type 'type2' to Python object
This commit is contained in:
Jason Rhinelander 2017-04-05 10:51:02 -04:00
parent 8f010cce8e
commit 6906b270d6
3 changed files with 23 additions and 6 deletions
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11
include/pybind11/cast.h
View File

@ -1246,18 +1246,19 @@ NAMESPACE_END(detail)
template <return_value_policy policy = return_value_policy::automatic_reference, template <return_value_policy policy = return_value_policy::automatic_reference,
typename... Args> tuple make_tuple(Args&&... args_) { typename... Args> tuple make_tuple(Args&&... args_) {
const size_t size = sizeof...(Args); constexpr size_t size = sizeof...(Args);
std::array<object, size> args { std::array<object, size> args {
{ reinterpret_steal<object>(detail::make_caster<Args>::cast( { reinterpret_steal<object>(detail::make_caster<Args>::cast(
std::forward<Args>(args_), policy, nullptr))... } std::forward<Args>(args_), policy, nullptr))... }
}; };
for (auto &arg_value : args) { for (size_t i = 0; i < args.size(); i++) {
if (!arg_value) { if (!args[i]) {
#if defined(NDEBUG) #if defined(NDEBUG)
throw cast_error("make_tuple(): unable to convert arguments to Python object (compile in debug mode for details)"); throw cast_error("make_tuple(): unable to convert arguments to Python object (compile in debug mode for details)");
#else #else
throw cast_error("make_tuple(): unable to convert arguments of types '" + std::array<std::string, size> argtypes { type_id<Args>()... };
(std::string) type_id<std::tuple<Args...>>() + "' to Python object"); throw cast_error("make_tuple(): unable to convert argument of type '" +
argtypes[i] + "' to Python object");
#endif #endif
} }
} }

8
tests/test_python_types.cpp
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@ -186,6 +186,7 @@ struct MoveOutContainer {
std::list<Value> move_list() const { return {{0}, {1}, {2}}; } std::list<Value> move_list() const { return {{0}, {1}, {2}}; }
}; };
struct UnregisteredType { };
test_initializer python_types([](py::module &m) { test_initializer python_types([](py::module &m) {
/* No constructor is explicitly defined below. An exception is raised when /* No constructor is explicitly defined below. An exception is raised when
@ -235,6 +236,13 @@ test_initializer python_types([](py::module &m) {
py::print("{a} + {b} = {c}"_s.format("a"_a="py::print", "b"_a="str.format", "c"_a="this")); py::print("{a} + {b} = {c}"_s.format("a"_a="py::print", "b"_a="str.format", "c"_a="this"));
}); });
m.def("test_print_failure", []() { py::print(42, UnregisteredType()); });
#if !defined(NDEBUG)
m.attr("debug_enabled") = true;
#else
m.attr("debug_enabled") = false;
#endif
m.def("test_str_format", []() { m.def("test_str_format", []() {
auto s1 = "{} + {} = {}"_s.format(1, 2, 3); auto s1 = "{} + {} = {}"_s.format(1, 2, 3);
auto s2 = "{a} + {b} = {c}"_s.format("a"_a=1, "b"_a=2, "c"_a=3); auto s2 = "{a} + {b} = {c}"_s.format("a"_a=1, "b"_a=2, "c"_a=3);

10
tests/test_python_types.py
View File

@ -258,7 +258,7 @@ def test_module():
def test_print(capture): def test_print(capture):
from pybind11_tests import test_print_function from pybind11_tests import test_print_function, test_print_failure, debug_enabled
with capture: with capture:
test_print_function() test_print_function()
@ -272,6 +272,14 @@ def test_print(capture):
""" """
assert capture.stderr == "this goes to stderr" assert capture.stderr == "this goes to stderr"
with pytest.raises(RuntimeError) as excinfo:
test_print_failure()
assert str(excinfo.value) == "make_tuple(): unable to convert " + (
"argument of type 'UnregisteredType' to Python object"
if debug_enabled else
"arguments to Python object (compile in debug mode for details)"
)
def test_str_api(): def test_str_api():
from pybind11_tests import test_str_format from pybind11_tests import test_str_format