Function Vector_angle

source/blender/python/mathutils/mathutils_Vector.cc:1152–1203

    "   :return: angle in radians or fallback when given\n"
    "   :rtype: float | Any\n");
static PyObject *Vector_angle(VectorObject *self, PyObject *args)
{
  const int vec_num = std::min(self->vec_num, 3); /* 4D angle makes no sense */
  float tvec[MAX_DIMENSIONS];
  PyObject *value;
  double dot = 0.0f, dot_self = 0.0f, dot_other = 0.0f;
  int x;
  PyObject *fallback = nullptr;

  if (!PyArg_ParseTuple(args, "O|O:angle", &value, &fallback)) {
    return nullptr;
  }

  if (BaseMath_ReadCallback(self) == -1) {
    return nullptr;
  }

  /* don't use clamped size, rule of thumb is vector sizes must match,
   * even though n this case 'w' is ignored */
  if (mathutils_array_parse(
          tvec, self->vec_num, self->vec_num, value, "Vector.angle(other), invalid 'other' arg") ==
      -1)
  {
    return nullptr;
  }

  if (self->vec_num > 4) {
    PyErr_SetString(PyExc_ValueError, "Vector must be 2D, 3D or 4D");
    return nullptr;
  }

  for (x = 0; x < vec_num; x++) {
    dot_self += double(self->vec[x]) * double(self->vec[x]);
    dot_other += double(tvec[x]) * double(tvec[x]);
    dot += double(self->vec[x]) * double(tvec[x]);
  }

  if (!dot_self || !dot_other) {
    /* avoid exception */
    if (fallback) {
      Py_INCREF(fallback);
      return fallback;
    }

    PyErr_SetString(PyExc_ValueError,
                    "Vector.angle(other): "
                    "zero length vectors have no valid angle");
    return nullptr;
  }

  return PyFloat_FromDouble(safe_acosf(dot / (sqrt(dot_self) * sqrt(dot_other))));
}

/** \} */