Fix /= operator under Python 3

The Python method for /= was set as `__idiv__`, which should be
`__itruediv__` under Python 3.

This wasn't totally broken in that without it defined, Python constructs
a new object by calling __truediv__.  The operator tests, however,
didn't actually test the /= operator: when I added it, I saw an extra
construction, leading to the problem.  This commit also includes tests
for the previously untested *= operator, and adds some element-wise
vector multiplication and division operators.

include/pybind11/operators.h

@@ -25,7 +25,7 @@ enum op_id : int {
     op_int, op_long, op_float, op_str, op_cmp, op_gt, op_ge, op_lt, op_le,
     op_eq, op_ne, op_iadd, op_isub, op_imul, op_idiv, op_imod, op_ilshift,
     op_irshift, op_iand, op_ixor, op_ior, op_complex, op_bool, op_nonzero,
-    op_repr, op_truediv
+    op_repr, op_truediv, op_itruediv
 };
 
 enum op_type : int {
@@ -129,7 +129,11 @@ PYBIND11_BINARY_OPERATOR(le,        ge,           operator<=,   l <= r)
 PYBIND11_INPLACE_OPERATOR(iadd,     operator+=,   l += r)
 PYBIND11_INPLACE_OPERATOR(isub,     operator-=,   l -= r)
 PYBIND11_INPLACE_OPERATOR(imul,     operator*=,   l *= r)
+#if PY_MAJOR_VERSION >= 3
+PYBIND11_INPLACE_OPERATOR(itruediv, operator/=,   l /= r)
+#else
 PYBIND11_INPLACE_OPERATOR(idiv,     operator/=,   l /= r)
+#endif
 PYBIND11_INPLACE_OPERATOR(imod,     operator%=,   l %= r)
 PYBIND11_INPLACE_OPERATOR(ilshift,  operator<<=,  l <<= r)
 PYBIND11_INPLACE_OPERATOR(irshift,  operator>>=,  l >>= r)

tests/test_operator_overloading.cpp

@@ -39,10 +39,14 @@ public:
     Vector2 operator+(float value) const { return Vector2(x + value, y + value); }
     Vector2 operator*(float value) const { return Vector2(x * value, y * value); }
     Vector2 operator/(float value) const { return Vector2(x / value, y / value); }
+    Vector2 operator*(const Vector2 &v) const { return Vector2(x * v.x, y * v.y); }
+    Vector2 operator/(const Vector2 &v) const { return Vector2(x / v.x, y / v.y); }
     Vector2& operator+=(const Vector2 &v) { x += v.x; y += v.y; return *this; }
     Vector2& operator-=(const Vector2 &v) { x -= v.x; y -= v.y; return *this; }
     Vector2& operator*=(float v) { x *= v; y *= v; return *this; }
     Vector2& operator/=(float v) { x /= v; y /= v; return *this; }
+    Vector2& operator*=(const Vector2 &v) { x *= v.x; y *= v.y; return *this; }
+    Vector2& operator/=(const Vector2 &v) { x /= v.x; y /= v.y; return *this; }
 
     friend Vector2 operator+(float f, const Vector2 &v) { return Vector2(f + v.x, f + v.y); }
     friend Vector2 operator-(float f, const Vector2 &v) { return Vector2(f - v.x, f - v.y); }
@@ -61,10 +65,14 @@ test_initializer operator_overloading([](py::module &m) {
         .def(py::self - float())
         .def(py::self * float())
         .def(py::self / float())
+        .def(py::self * py::self)
+        .def(py::self / py::self)
         .def(py::self += py::self)
         .def(py::self -= py::self)
         .def(py::self *= float())
         .def(py::self /= float())
+        .def(py::self *= py::self)
+        .def(py::self /= py::self)
         .def(float() + py::self)
         .def(float() - py::self)
         .def(float() * py::self)

tests/test_operator_overloading.py

@@ -16,10 +16,21 @@ def test_operator_overloading():
     assert str(8 + v1) == "[9.000000, 10.000000]"
     assert str(8 * v1) == "[8.000000, 16.000000]"
     assert str(8 / v1) == "[8.000000, 4.000000]"
+    assert str(v1 * v2) == "[3.000000, -2.000000]"
+    assert str(v2 / v1) == "[3.000000, -0.500000]"
 
-    v1 += v2
+    v1 += 2 * v2
+    assert str(v1) == "[7.000000, 0.000000]"
+    v1 -= v2
+    assert str(v1) == "[4.000000, 1.000000]"
     v1 *= 2
     assert str(v1) == "[8.000000, 2.000000]"
+    v1 /= 16
+    assert str(v1) == "[0.500000, 0.125000]"
+    v1 *= v2
+    assert str(v1) == "[1.500000, -0.125000]"
+    v2 /= v1
+    assert str(v2) == "[2.000000, 8.000000]"
 
     cstats = ConstructorStats.get(Vector2)
     assert cstats.alive() == 2
@@ -32,7 +43,9 @@ def test_operator_overloading():
                                '[-7.000000, -6.000000]', '[9.000000, 10.000000]',
                                '[8.000000, 16.000000]', '[0.125000, 0.250000]',
                                '[7.000000, 6.000000]', '[9.000000, 10.000000]',
-                               '[8.000000, 16.000000]', '[8.000000, 4.000000]']
+                               '[8.000000, 16.000000]', '[8.000000, 4.000000]',
+                               '[3.000000, -2.000000]', '[3.000000, -0.500000]',
+                               '[6.000000, -2.000000]']
     assert cstats.default_constructions == 0
     assert cstats.copy_constructions == 0
     assert cstats.move_constructions >= 10