Add py::str::format() method

include/pybind11/pytypes.h

@@ -385,8 +385,18 @@ public:
             pybind11_fail("Unable to extract string contents! (invalid type)");
         return std::string(buffer, (size_t) length);
     }
+
+    template <typename... Args>
+    str format(Args &&...args) const {
+        return attr("format").cast<object>()(std::forward<Args>(args)...);
+    }
 };
 
+inline namespace literals {
+/// String literal version of str
+inline str operator"" _s(const char *s, size_t size) { return {s, size}; }
+}
+
 inline pybind11::str handle::str() const {
     PyObject *strValue = PyObject_Str(m_ptr);
 #if PY_MAJOR_VERSION < 3

tests/test_python_types.cpp

@@ -210,5 +210,13 @@ test_initializer python_types([](py::module &m) {
         py::print("this goes to stderr", "file"_a=py_stderr);
 
         py::print("flush", "flush"_a=true);
+
+        py::print("{a} + {b} = {c}"_s.format("a"_a="py::print", "b"_a="str.format", "c"_a="this"));
+    });
+
+    m.def("test_str_format", []() {
+        auto s1 = "{} + {} = {}"_s.format(1, 2, 3);
+        auto s2 = "{a} + {b} = {c}"_s.format("a"_a=1, "b"_a=2, "c"_a=3);
+        return py::make_tuple(s1, s2);
     });
 });

tests/test_python_types.py

@@ -231,5 +231,14 @@ def test_print(capture):
         *args-and-a-custom-separator
         no new line here -- next print
         flush
+        py::print + str.format = this
     """
     assert capture.stderr == "this goes to stderr"
+
+
+def test_str_api():
+    from pybind11_tests import test_str_format
+
+    s1, s2 = test_str_format()
+    assert s1 == "1 + 2 = 3"
+    assert s1 == s2